When adding separate memory blocks via add_memory*() and onlining them
immediately, the metadata (especially the memmap) of the next block will be
placed onto one of the just added+onlined block. This creates a chain
of unmovable allocations: If the last memory block cannot get
offlined+removed() so will all dependent ones. We directly have unmovable
allocations all over the place.
This can be observed quite easily using virtio-mem, however, it can also
be observed when using DIMMs. The freshly onlined pages will usually be
placed to the head of the freelists, meaning they will be allocated next,
turning the just-added memory usually immediately un-removable. The
fresh pages are cold, prefering to allocate others (that might be hot)
also feels to be the natural thing to do.
It also applies to the hyper-v balloon xen-balloon, and ppc64 dlpar: when
adding separate, successive memory blocks, each memory block will have
unmovable allocations on them - for example gigantic pages will fail to
allocate.
While the ZONE_NORMAL doesn't provide any guarantees that memory can get
offlined+removed again (any kind of fragmentation with unmovable
allocations is possible), there are many scenarios (hotplugging a lot of
memory, running workload, hotunplug some memory/as much as possible) where
we can offline+remove quite a lot with this patchset.
a) To visualize the problem, a very simple example:
Start a VM with 4GB and 8GB of virtio-mem memory:
[root@localhost ~]# lsmem
RANGE SIZE STATE REMOVABLE BLOCK
0x0000000000000000-0x00000000bfffffff 3G online yes 0-23
0x0000000100000000-0x000000033fffffff 9G online yes 32-103
Memory block size: 128M
Total online memory: 12G
Total offline memory: 0B
Then try to unplug as much as possible using virtio-mem. Observe which
memory blocks are still around. Without this patch set:
[root@localhost ~]# lsmem
RANGE SIZE STATE REMOVABLE BLOCK
0x0000000000000000-0x00000000bfffffff 3G online yes 0-23
0x0000000100000000-0x000000013fffffff 1G online yes 32-39
0x0000000148000000-0x000000014fffffff 128M online yes 41
0x0000000158000000-0x000000015fffffff 128M online yes 43
0x0000000168000000-0x000000016fffffff 128M online yes 45
0x0000000178000000-0x000000017fffffff 128M online yes 47
0x0000000188000000-0x0000000197ffffff 256M online yes 49-50
0x00000001a0000000-0x00000001a7ffffff 128M online yes 52
0x00000001b0000000-0x00000001b7ffffff 128M online yes 54
0x00000001c0000000-0x00000001c7ffffff 128M online yes 56
0x00000001d0000000-0x00000001d7ffffff 128M online yes 58
0x00000001e0000000-0x00000001e7ffffff 128M online yes 60
0x00000001f0000000-0x00000001f7ffffff 128M online yes 62
0x0000000200000000-0x0000000207ffffff 128M online yes 64
0x0000000210000000-0x0000000217ffffff 128M online yes 66
0x0000000220000000-0x0000000227ffffff 128M online yes 68
0x0000000230000000-0x0000000237ffffff 128M online yes 70
0x0000000240000000-0x0000000247ffffff 128M online yes 72
0x0000000250000000-0x0000000257ffffff 128M online yes 74
0x0000000260000000-0x0000000267ffffff 128M online yes 76
0x0000000270000000-0x0000000277ffffff 128M online yes 78
0x0000000280000000-0x0000000287ffffff 128M online yes 80
0x0000000290000000-0x0000000297ffffff 128M online yes 82
0x00000002a0000000-0x00000002a7ffffff 128M online yes 84
0x00000002b0000000-0x00000002b7ffffff 128M online yes 86
0x00000002c0000000-0x00000002c7ffffff 128M online yes 88
0x00000002d0000000-0x00000002d7ffffff 128M online yes 90
0x00000002e0000000-0x00000002e7ffffff 128M online yes 92
0x00000002f0000000-0x00000002f7ffffff 128M online yes 94
0x0000000300000000-0x0000000307ffffff 128M online yes 96
0x0000000310000000-0x0000000317ffffff 128M online yes 98
0x0000000320000000-0x0000000327ffffff 128M online yes 100
0x0000000330000000-0x000000033fffffff 256M online yes 102-103
Memory block size: 128M
Total online memory: 8.1G
Total offline memory: 0B
With this patch set:
[root@localhost ~]# lsmem
RANGE SIZE STATE REMOVABLE BLOCK
0x0000000000000000-0x00000000bfffffff 3G online yes 0-23
0x0000000100000000-0x000000013fffffff 1G online yes 32-39
Memory block size: 128M
Total online memory: 4G
Total offline memory: 0B
All memory can get unplugged, all memory block can get removed. Of course,
no workload ran and the system was basically idle, but it highlights the
issue - the fairly deterministic chain of unmovable allocations. When a
huge page for the 2MB memmap is needed, a just-onlined 4MB page will
be split. The remaining 2MB page will be used for the memmap of the next
memory block. So one memory block will hold the memmap of the two following
memory blocks. Finally the pages of the last-onlined memory block will get
used for the next bigger allocations - if any allocation is unmovable,
all dependent memory blocks cannot get unplugged and removed until that
allocation is gone.
Note that with bigger memory blocks (e.g., 256MB), *all* memory
blocks are dependent and none can get unplugged again!
b) Experiment with memory intensive workload
I performed an experiment with an older version of this patch set
(before we used undo_isolate_page_range() in online_pages():
Hotplug 56GB to a VM with an initial 4GB, onlining all memory to
ZONE_NORMAL right from the kernel when adding it. I then run various
memory intensive workloads that consume most system memory for a total of
45 minutes. Once finished, I try to unplug as much memory as possible.
With this change, I am able to remove via virtio-mem (adding individual
128MB memory blocks) 413 out of 448 added memory blocks. Via individual
(256MB) DIMMs 380 out of 448 added memory blocks. (I don't have any numbers
without this patchset, but looking at the above example, it's at most half
of the 448 memory blocks for virtio-mem, and most probably none for DIMMs).
Again, there are workloads that might behave very differently due to the
nature of ZONE_NORMAL.
This change also affects (besodes memory onlining):
- Other users of undo_isolate_page_range(): Pages are always placed to the
tail.
-- When memory offlining fails
-- When memory isolation fails after having isolated some pageblocks
-- When alloc_contig_range() either succeeds or fails
- Other users of __putback_isolated_page(): Pages are always placed to the
tail.
-- Free page reporting
- Other users of __free_pages_core()
-- AFAIKs, any memory that is getting exposed to the buddy during boot.
IIUC we will now usually allocate memory from lower addresses within
a zone first (especially during boot).
- Other users of generic_online_page()
-- Hyper-V balloon
RFC -> v1:
- Tweak some patch descriptions
- "mm/page_alloc: place pages to tail in __putback_isolated_page()"
-- FOP_TO_TAIL now has higher precedence than page shuffling
-- Add a note that nothing should rely on FOP_TO_TAIL for correctness
- "mm/page_alloc: always move pages to the tail of the freelist in
unset_migratetype_isolate()"
-- Use "bool" parameter for move_freepages_block() as requested
- "mm/page_alloc: place pages to tail in __free_pages_core()"
-- Eliminate set_page_refcounted() + page_ref_dec() and add a comment
- "mm/memory_hotplug: update comment regarding zone shuffling"
-- Added
David Hildenbrand (5):
mm/page_alloc: convert "report" flag of __free_one_page() to a proper
flag
mm/page_alloc: place pages to tail in __putback_isolated_page()
mm/page_alloc: always move pages to the tail of the freelist in
unset_migratetype_isolate()
mm/page_alloc: place pages to tail in __free_pages_core()
mm/memory_hotplug: update comment regarding zone shuffling
include/linux/page-isolation.h | 4 +-
mm/memory_hotplug.c | 11 ++--
mm/page_alloc.c | 114 ++++++++++++++++++++++++---------
mm/page_isolation.c | 12 +++-
4 files changed, 97 insertions(+), 44 deletions(-)
--
2.26.2
Let's prepare for additional flags and avoid long parameter lists of bools.
Follow-up patches will also make use of the flags in __free_pages_ok(),
however, I wasn't able to come up with a better name for the type - should
be good enough for internal purposes.
Reviewed-by: Alexander Duyck <[email protected]>
Reviewed-by: Vlastimil Babka <[email protected]>
Reviewed-by: Oscar Salvador <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Alexander Duyck <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Wei Yang <[email protected]>
Cc: Oscar Salvador <[email protected]>
Cc: Mike Rapoport <[email protected]>
Signed-off-by: David Hildenbrand <[email protected]>
---
mm/page_alloc.c | 28 ++++++++++++++++++++--------
1 file changed, 20 insertions(+), 8 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index df90e3654f97..daab90e960fe 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -77,6 +77,18 @@
#include "shuffle.h"
#include "page_reporting.h"
+/* Free One Page flags: for internal, non-pcp variants of free_pages(). */
+typedef int __bitwise fop_t;
+
+/* No special request */
+#define FOP_NONE ((__force fop_t)0)
+
+/*
+ * Skip free page reporting notification for the (possibly merged) page. (will
+ * *not* mark the page reported, only skip the notification).
+ */
+#define FOP_SKIP_REPORT_NOTIFY ((__force fop_t)BIT(0))
+
/* prevent >1 _updater_ of zone percpu pageset ->high and ->batch fields */
static DEFINE_MUTEX(pcp_batch_high_lock);
#define MIN_PERCPU_PAGELIST_FRACTION (8)
@@ -948,10 +960,9 @@ buddy_merge_likely(unsigned long pfn, unsigned long buddy_pfn,
* -- nyc
*/
-static inline void __free_one_page(struct page *page,
- unsigned long pfn,
- struct zone *zone, unsigned int order,
- int migratetype, bool report)
+static inline void __free_one_page(struct page *page, unsigned long pfn,
+ struct zone *zone, unsigned int order,
+ int migratetype, fop_t fop_flags)
{
struct capture_control *capc = task_capc(zone);
unsigned long buddy_pfn;
@@ -1038,7 +1049,7 @@ static inline void __free_one_page(struct page *page,
add_to_free_list(page, zone, order, migratetype);
/* Notify page reporting subsystem of freed page */
- if (report)
+ if (!(fop_flags & FOP_SKIP_REPORT_NOTIFY))
page_reporting_notify_free(order);
}
@@ -1379,7 +1390,7 @@ static void free_pcppages_bulk(struct zone *zone, int count,
if (unlikely(isolated_pageblocks))
mt = get_pageblock_migratetype(page);
- __free_one_page(page, page_to_pfn(page), zone, 0, mt, true);
+ __free_one_page(page, page_to_pfn(page), zone, 0, mt, FOP_NONE);
trace_mm_page_pcpu_drain(page, 0, mt);
}
spin_unlock(&zone->lock);
@@ -1395,7 +1406,7 @@ static void free_one_page(struct zone *zone,
is_migrate_isolate(migratetype))) {
migratetype = get_pfnblock_migratetype(page, pfn);
}
- __free_one_page(page, pfn, zone, order, migratetype, true);
+ __free_one_page(page, pfn, zone, order, migratetype, FOP_NONE);
spin_unlock(&zone->lock);
}
@@ -3288,7 +3299,8 @@ void __putback_isolated_page(struct page *page, unsigned int order, int mt)
lockdep_assert_held(&zone->lock);
/* Return isolated page to tail of freelist. */
- __free_one_page(page, page_to_pfn(page), zone, order, mt, false);
+ __free_one_page(page, page_to_pfn(page), zone, order, mt,
+ FOP_SKIP_REPORT_NOTIFY);
}
/*
--
2.26.2
__putback_isolated_page() already documents that pages will be placed to
the tail of the freelist - this is, however, not the case for
"order >= MAX_ORDER - 2" (see buddy_merge_likely()) - which should be
the case for all existing users.
This change affects two users:
- free page reporting
- page isolation, when undoing the isolation (including memory onlining).
This behavior is desireable for pages that haven't really been touched
lately, so exactly the two users that don't actually read/write page
content, but rather move untouched pages.
The new behavior is especially desirable for memory onlining, where we
allow allocation of newly onlined pages via undo_isolate_page_range()
in online_pages(). Right now, we always place them to the head of the
free list, resulting in undesireable behavior: Assume we add
individual memory chunks via add_memory() and online them right away to
the NORMAL zone. We create a dependency chain of unmovable allocations
e.g., via the memmap. The memmap of the next chunk will be placed onto
previous chunks - if the last block cannot get offlined+removed, all
dependent ones cannot get offlined+removed. While this can already be
observed with individual DIMMs, it's more of an issue for virtio-mem
(and I suspect also ppc DLPAR).
Document that this should only be used for optimizations, and no code
should realy on this for correction (if the order of freepage lists
ever changes).
We won't care about page shuffling: memory onlining already properly
shuffles after onlining. free page reporting doesn't care about
physically contiguous ranges, and there are already cases where page
isolation will simply move (physically close) free pages to (currently)
the head of the freelists via move_freepages_block() instead of
shuffling. If this becomes ever relevant, we should shuffle the whole
zone when undoing isolation of larger ranges, and after
free_contig_range().
Reviewed-by: Alexander Duyck <[email protected]>
Reviewed-by: Oscar Salvador <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Alexander Duyck <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Wei Yang <[email protected]>
Cc: Oscar Salvador <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Scott Cheloha <[email protected]>
Cc: Michael Ellerman <[email protected]>
Signed-off-by: David Hildenbrand <[email protected]>
---
mm/page_alloc.c | 18 ++++++++++++++++--
1 file changed, 16 insertions(+), 2 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index daab90e960fe..9e3ed4a6f69a 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -89,6 +89,18 @@ typedef int __bitwise fop_t;
*/
#define FOP_SKIP_REPORT_NOTIFY ((__force fop_t)BIT(0))
+/*
+ * Place the (possibly merged) page to the tail of the freelist. Will ignore
+ * page shuffling (relevant code - e.g., memory onlining - is expected to
+ * shuffle the whole zone).
+ *
+ * Note: No code should rely onto this flag for correctness - it's purely
+ * to allow for optimizations when handing back either fresh pages
+ * (memory onlining) or untouched pages (page isolation, free page
+ * reporting).
+ */
+#define FOP_TO_TAIL ((__force fop_t)BIT(1))
+
/* prevent >1 _updater_ of zone percpu pageset ->high and ->batch fields */
static DEFINE_MUTEX(pcp_batch_high_lock);
#define MIN_PERCPU_PAGELIST_FRACTION (8)
@@ -1038,7 +1050,9 @@ static inline void __free_one_page(struct page *page, unsigned long pfn,
done_merging:
set_page_order(page, order);
- if (is_shuffle_order(order))
+ if (fop_flags & FOP_TO_TAIL)
+ to_tail = true;
+ else if (is_shuffle_order(order))
to_tail = shuffle_pick_tail();
else
to_tail = buddy_merge_likely(pfn, buddy_pfn, page, order);
@@ -3300,7 +3314,7 @@ void __putback_isolated_page(struct page *page, unsigned int order, int mt)
/* Return isolated page to tail of freelist. */
__free_one_page(page, page_to_pfn(page), zone, order, mt,
- FOP_SKIP_REPORT_NOTIFY);
+ FOP_SKIP_REPORT_NOTIFY | FOP_TO_TAIL);
}
/*
--
2.26.2
Page isolation doesn't actually touch the pages, it simply isolates
pageblocks and moves all free pages to the MIGRATE_ISOLATE freelist.
We already place pages to the tail of the freelists when undoing
isolation via __putback_isolated_page(), let's do it in any case
(e.g., if order <= pageblock_order) and document the behavior.
Add a "to_tail" parameter to move_freepages_block() but introduce a
a new move_to_free_list_tail() - similar to add_to_free_list_tail().
This change results in all pages getting onlined via online_pages() to
be placed to the tail of the freelist.
Reviewed-by: Oscar Salvador <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Alexander Duyck <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Wei Yang <[email protected]>
Cc: Oscar Salvador <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Scott Cheloha <[email protected]>
Cc: Michael Ellerman <[email protected]>
Signed-off-by: David Hildenbrand <[email protected]>
---
include/linux/page-isolation.h | 4 ++--
mm/page_alloc.c | 35 +++++++++++++++++++++++-----------
mm/page_isolation.c | 12 +++++++++---
3 files changed, 35 insertions(+), 16 deletions(-)
diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h
index 572458016331..3eca9b3c5305 100644
--- a/include/linux/page-isolation.h
+++ b/include/linux/page-isolation.h
@@ -36,8 +36,8 @@ static inline bool is_migrate_isolate(int migratetype)
struct page *has_unmovable_pages(struct zone *zone, struct page *page,
int migratetype, int flags);
void set_pageblock_migratetype(struct page *page, int migratetype);
-int move_freepages_block(struct zone *zone, struct page *page,
- int migratetype, int *num_movable);
+int move_freepages_block(struct zone *zone, struct page *page, int migratetype,
+ bool to_tail, int *num_movable);
/*
* Changes migrate type in [start_pfn, end_pfn) to be MIGRATE_ISOLATE.
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 9e3ed4a6f69a..d5a5f528b8ca 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -905,6 +905,15 @@ static inline void move_to_free_list(struct page *page, struct zone *zone,
list_move(&page->lru, &area->free_list[migratetype]);
}
+/* Used for pages which are on another list */
+static inline void move_to_free_list_tail(struct page *page, struct zone *zone,
+ unsigned int order, int migratetype)
+{
+ struct free_area *area = &zone->free_area[order];
+
+ list_move_tail(&page->lru, &area->free_list[migratetype]);
+}
+
static inline void del_page_from_free_list(struct page *page, struct zone *zone,
unsigned int order)
{
@@ -2338,9 +2347,9 @@ static inline struct page *__rmqueue_cma_fallback(struct zone *zone,
* Note that start_page and end_pages are not aligned on a pageblock
* boundary. If alignment is required, use move_freepages_block()
*/
-static int move_freepages(struct zone *zone,
- struct page *start_page, struct page *end_page,
- int migratetype, int *num_movable)
+static int move_freepages(struct zone *zone, struct page *start_page,
+ struct page *end_page, int migratetype,
+ bool to_tail, int *num_movable)
{
struct page *page;
unsigned int order;
@@ -2371,7 +2380,10 @@ static int move_freepages(struct zone *zone,
VM_BUG_ON_PAGE(page_zone(page) != zone, page);
order = page_order(page);
- move_to_free_list(page, zone, order, migratetype);
+ if (to_tail)
+ move_to_free_list_tail(page, zone, order, migratetype);
+ else
+ move_to_free_list(page, zone, order, migratetype);
page += 1 << order;
pages_moved += 1 << order;
}
@@ -2379,8 +2391,8 @@ static int move_freepages(struct zone *zone,
return pages_moved;
}
-int move_freepages_block(struct zone *zone, struct page *page,
- int migratetype, int *num_movable)
+int move_freepages_block(struct zone *zone, struct page *page, int migratetype,
+ bool to_tail, int *num_movable)
{
unsigned long start_pfn, end_pfn;
struct page *start_page, *end_page;
@@ -2401,7 +2413,7 @@ int move_freepages_block(struct zone *zone, struct page *page,
return 0;
return move_freepages(zone, start_page, end_page, migratetype,
- num_movable);
+ to_tail, num_movable);
}
static void change_pageblock_range(struct page *pageblock_page,
@@ -2526,8 +2538,8 @@ static void steal_suitable_fallback(struct zone *zone, struct page *page,
if (!whole_block)
goto single_page;
- free_pages = move_freepages_block(zone, page, start_type,
- &movable_pages);
+ free_pages = move_freepages_block(zone, page, start_type, false,
+ &movable_pages);
/*
* Determine how many pages are compatible with our allocation.
* For movable allocation, it's the number of movable pages which
@@ -2635,7 +2647,8 @@ static void reserve_highatomic_pageblock(struct page *page, struct zone *zone,
&& !is_migrate_cma(mt)) {
zone->nr_reserved_highatomic += pageblock_nr_pages;
set_pageblock_migratetype(page, MIGRATE_HIGHATOMIC);
- move_freepages_block(zone, page, MIGRATE_HIGHATOMIC, NULL);
+ move_freepages_block(zone, page, MIGRATE_HIGHATOMIC, false,
+ NULL);
}
out_unlock:
@@ -2711,7 +2724,7 @@ static bool unreserve_highatomic_pageblock(const struct alloc_context *ac,
*/
set_pageblock_migratetype(page, ac->migratetype);
ret = move_freepages_block(zone, page, ac->migratetype,
- NULL);
+ false, NULL);
if (ret) {
spin_unlock_irqrestore(&zone->lock, flags);
return ret;
diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index abfe26ad59fd..de44e1329706 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -45,7 +45,7 @@ static int set_migratetype_isolate(struct page *page, int migratetype, int isol_
set_pageblock_migratetype(page, MIGRATE_ISOLATE);
zone->nr_isolate_pageblock++;
nr_pages = move_freepages_block(zone, page, MIGRATE_ISOLATE,
- NULL);
+ false, NULL);
__mod_zone_freepage_state(zone, -nr_pages, mt);
spin_unlock_irqrestore(&zone->lock, flags);
@@ -83,7 +83,7 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype)
* Because freepage with more than pageblock_order on isolated
* pageblock is restricted to merge due to freepage counting problem,
* it is possible that there is free buddy page.
- * move_freepages_block() doesn't care of merge so we need other
+ * move_freepages_block() don't care about merging, so we need another
* approach in order to merge them. Isolation and free will make
* these pages to be merged.
*/
@@ -106,9 +106,15 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype)
* If we isolate freepage with more than pageblock_order, there
* should be no freepage in the range, so we could avoid costly
* pageblock scanning for freepage moving.
+ *
+ * We didn't actually touch any of the isolated pages, so place them
+ * to the tail of the freelist. This is an optimization for memory
+ * onlining - just onlined memory won't immediately be considered for
+ * allocation.
*/
if (!isolated_page) {
- nr_pages = move_freepages_block(zone, page, migratetype, NULL);
+ nr_pages = move_freepages_block(zone, page, migratetype, true,
+ NULL);
__mod_zone_freepage_state(zone, nr_pages, migratetype);
}
set_pageblock_migratetype(page, migratetype);
--
2.26.2
As we no longer shuffle via generic_online_page() and when undoing
isolation, we can simplify the comment.
We now effectively shuffle only once (properly) when onlining new
memory.
Cc: Andrew Morton <[email protected]>
Cc: Alexander Duyck <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Wei Yang <[email protected]>
Cc: Oscar Salvador <[email protected]>
Cc: Mike Rapoport <[email protected]>
Signed-off-by: David Hildenbrand <[email protected]>
---
mm/memory_hotplug.c | 11 ++++-------
1 file changed, 4 insertions(+), 7 deletions(-)
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 9db80ee29caa..c589bd8801bb 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -859,13 +859,10 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
undo_isolate_page_range(pfn, pfn + nr_pages, MIGRATE_MOVABLE);
/*
- * When exposing larger, physically contiguous memory areas to the
- * buddy, shuffling in the buddy (when freeing onlined pages, putting
- * them either to the head or the tail of the freelist) is only helpful
- * for maintaining the shuffle, but not for creating the initial
- * shuffle. Shuffle the whole zone to make sure the just onlined pages
- * are properly distributed across the whole freelist. Make sure to
- * shuffle once pageblocks are no longer isolated.
+ * Freshly onlined pages aren't shuffled (e.g., all pages are placed to
+ * the tail of the freelist when undoing isolation). Shuffle the whole
+ * zone to make sure the just onlined pages are properly distributed
+ * across the whole freelist - to create an initial shuffle.
*/
shuffle_zone(zone);
--
2.26.2
__free_pages_core() is used when exposing fresh memory to the buddy
during system boot and when onlining memory in generic_online_page().
generic_online_page() is used in two cases:
1. Direct memory onlining in online_pages().
2. Deferred memory onlining in memory-ballooning-like mechanisms (HyperV
balloon and virtio-mem), when parts of a section are kept
fake-offline to be fake-onlined later on.
In 1, we already place pages to the tail of the freelist. Pages will be
freed to MIGRATE_ISOLATE lists first and moved to the tail of the freelists
via undo_isolate_page_range().
In 2, we currently don't implement a proper rule. In case of virtio-mem,
where we currently always online MAX_ORDER - 1 pages, the pages will be
placed to the HEAD of the freelist - undesireable. While the hyper-v
balloon calls generic_online_page() with single pages, usually it will
call it on successive single pages in a larger block.
The pages are fresh, so place them to the tail of the freelists and avoid
the PCP. In __free_pages_core(), remove the now superflouos call to
set_page_refcounted() and add a comment regarding page initialization and
the refcount.
Note: In 2. we currently don't shuffle. If ever relevant (page shuffling
is usually of limited use in virtualized environments), we might want to
shuffle after a sequence of generic_online_page() calls in the
relevant callers.
Reviewed-by: Vlastimil Babka <[email protected]>
Reviewed-by: Oscar Salvador <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Alexander Duyck <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Wei Yang <[email protected]>
Cc: Oscar Salvador <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: "K. Y. Srinivasan" <[email protected]>
Cc: Haiyang Zhang <[email protected]>
Cc: Stephen Hemminger <[email protected]>
Cc: Wei Liu <[email protected]>
Signed-off-by: David Hildenbrand <[email protected]>
---
mm/page_alloc.c | 37 ++++++++++++++++++++++++-------------
1 file changed, 24 insertions(+), 13 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d5a5f528b8ca..8a2134fe9947 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -270,7 +270,8 @@ bool pm_suspended_storage(void)
unsigned int pageblock_order __read_mostly;
#endif
-static void __free_pages_ok(struct page *page, unsigned int order);
+static void __free_pages_ok(struct page *page, unsigned int order,
+ fop_t fop_flags);
/*
* results with 256, 32 in the lowmem_reserve sysctl:
@@ -682,7 +683,7 @@ static void bad_page(struct page *page, const char *reason)
void free_compound_page(struct page *page)
{
mem_cgroup_uncharge(page);
- __free_pages_ok(page, compound_order(page));
+ __free_pages_ok(page, compound_order(page), FOP_NONE);
}
void prep_compound_page(struct page *page, unsigned int order)
@@ -1419,17 +1420,15 @@ static void free_pcppages_bulk(struct zone *zone, int count,
spin_unlock(&zone->lock);
}
-static void free_one_page(struct zone *zone,
- struct page *page, unsigned long pfn,
- unsigned int order,
- int migratetype)
+static void free_one_page(struct zone *zone, struct page *page, unsigned long pfn,
+ unsigned int order, int migratetype, fop_t fop_flags)
{
spin_lock(&zone->lock);
if (unlikely(has_isolate_pageblock(zone) ||
is_migrate_isolate(migratetype))) {
migratetype = get_pfnblock_migratetype(page, pfn);
}
- __free_one_page(page, pfn, zone, order, migratetype, FOP_NONE);
+ __free_one_page(page, pfn, zone, order, migratetype, fop_flags);
spin_unlock(&zone->lock);
}
@@ -1507,7 +1506,8 @@ void __meminit reserve_bootmem_region(phys_addr_t start, phys_addr_t end)
}
}
-static void __free_pages_ok(struct page *page, unsigned int order)
+static void __free_pages_ok(struct page *page, unsigned int order,
+ fop_t fop_flags)
{
unsigned long flags;
int migratetype;
@@ -1519,7 +1519,8 @@ static void __free_pages_ok(struct page *page, unsigned int order)
migratetype = get_pfnblock_migratetype(page, pfn);
local_irq_save(flags);
__count_vm_events(PGFREE, 1 << order);
- free_one_page(page_zone(page), page, pfn, order, migratetype);
+ free_one_page(page_zone(page), page, pfn, order, migratetype,
+ fop_flags);
local_irq_restore(flags);
}
@@ -1529,6 +1530,11 @@ void __free_pages_core(struct page *page, unsigned int order)
struct page *p = page;
unsigned int loop;
+ /*
+ * When initializing the memmap, init_single_page() sets the refcount
+ * of all pages to 1 ("allocated"/"not free"). We have to set the
+ * refcount of all involved pages to 0.
+ */
prefetchw(p);
for (loop = 0; loop < (nr_pages - 1); loop++, p++) {
prefetchw(p + 1);
@@ -1539,8 +1545,12 @@ void __free_pages_core(struct page *page, unsigned int order)
set_page_count(p, 0);
atomic_long_add(nr_pages, &page_zone(page)->managed_pages);
- set_page_refcounted(page);
- __free_pages(page, order);
+
+ /*
+ * Bypass PCP and place fresh pages right to the tail, primarily
+ * relevant for memory onlining.
+ */
+ __free_pages_ok(page, order, FOP_TO_TAIL);
}
#ifdef CONFIG_NEED_MULTIPLE_NODES
@@ -3171,7 +3181,8 @@ static void free_unref_page_commit(struct page *page, unsigned long pfn)
*/
if (migratetype >= MIGRATE_PCPTYPES) {
if (unlikely(is_migrate_isolate(migratetype))) {
- free_one_page(zone, page, pfn, 0, migratetype);
+ free_one_page(zone, page, pfn, 0, migratetype,
+ FOP_NONE);
return;
}
migratetype = MIGRATE_MOVABLE;
@@ -5063,7 +5074,7 @@ static inline void free_the_page(struct page *page, unsigned int order)
if (order == 0) /* Via pcp? */
free_unref_page(page);
else
- __free_pages_ok(page, order);
+ __free_pages_ok(page, order, FOP_NONE);
}
void __free_pages(struct page *page, unsigned int order)
--
2.26.2
> Let's prepare for additional flags and avoid long parameter lists of bools.
> Follow-up patches will also make use of the flags in __free_pages_ok(),
> however, I wasn't able to come up with a better name for the type - should
> be good enough for internal purposes.
>
> Reviewed-by: Alexander Duyck <[email protected]>
> Reviewed-by: Vlastimil Babka <[email protected]>
> Reviewed-by: Oscar Salvador <[email protected]>
> Cc: Andrew Morton <[email protected]>
> Cc: Alexander Duyck <[email protected]>
> Cc: Mel Gorman <[email protected]>
> Cc: Michal Hocko <[email protected]>
> Cc: Dave Hansen <[email protected]>
> Cc: Vlastimil Babka <[email protected]>
> Cc: Wei Yang <[email protected]>
> Cc: Oscar Salvador <[email protected]>
> Cc: Mike Rapoport <[email protected]>
> Signed-off-by: David Hildenbrand <[email protected]>
> ---
> mm/page_alloc.c | 28 ++++++++++++++++++++--------
> 1 file changed, 20 insertions(+), 8 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index df90e3654f97..daab90e960fe 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -77,6 +77,18 @@
> #include "shuffle.h"
> #include "page_reporting.h"
>
> +/* Free One Page flags: for internal, non-pcp variants of free_pages(). */
> +typedef int __bitwise fop_t;
> +
> +/* No special request */
> +#define FOP_NONE ((__force fop_t)0)
> +
> +/*
> + * Skip free page reporting notification for the (possibly merged) page. (will
> + * *not* mark the page reported, only skip the notification).
> + */
> +#define FOP_SKIP_REPORT_NOTIFY ((__force fop_t)BIT(0))
> +
> /* prevent >1 _updater_ of zone percpu pageset ->high and ->batch fields */
> static DEFINE_MUTEX(pcp_batch_high_lock);
> #define MIN_PERCPU_PAGELIST_FRACTION (8)
> @@ -948,10 +960,9 @@ buddy_merge_likely(unsigned long pfn, unsigned long buddy_pfn,
> * -- nyc
> */
>
> -static inline void __free_one_page(struct page *page,
> - unsigned long pfn,
> - struct zone *zone, unsigned int order,
> - int migratetype, bool report)
> +static inline void __free_one_page(struct page *page, unsigned long pfn,
> + struct zone *zone, unsigned int order,
> + int migratetype, fop_t fop_flags)
> {
> struct capture_control *capc = task_capc(zone);
> unsigned long buddy_pfn;
> @@ -1038,7 +1049,7 @@ static inline void __free_one_page(struct page *page,
> add_to_free_list(page, zone, order, migratetype);
>
> /* Notify page reporting subsystem of freed page */
> - if (report)
> + if (!(fop_flags & FOP_SKIP_REPORT_NOTIFY))
> page_reporting_notify_free(order);
> }
>
> @@ -1379,7 +1390,7 @@ static void free_pcppages_bulk(struct zone *zone, int count,
> if (unlikely(isolated_pageblocks))
> mt = get_pageblock_migratetype(page);
>
> - __free_one_page(page, page_to_pfn(page), zone, 0, mt, true);
> + __free_one_page(page, page_to_pfn(page), zone, 0, mt, FOP_NONE);
> trace_mm_page_pcpu_drain(page, 0, mt);
> }
> spin_unlock(&zone->lock);
> @@ -1395,7 +1406,7 @@ static void free_one_page(struct zone *zone,
> is_migrate_isolate(migratetype))) {
> migratetype = get_pfnblock_migratetype(page, pfn);
> }
> - __free_one_page(page, pfn, zone, order, migratetype, true);
> + __free_one_page(page, pfn, zone, order, migratetype, FOP_NONE);
> spin_unlock(&zone->lock);
> }
>
> @@ -3288,7 +3299,8 @@ void __putback_isolated_page(struct page *page, unsigned int order, int mt)
> lockdep_assert_held(&zone->lock);
>
> /* Return isolated page to tail of freelist. */
> - __free_one_page(page, page_to_pfn(page), zone, order, mt, false);
> + __free_one_page(page, page_to_pfn(page), zone, order, mt,
> + FOP_SKIP_REPORT_NOTIFY);
> }
Reviewed-by: Pankaj Gupta <[email protected]>
> __free_pages_core() is used when exposing fresh memory to the buddy
> during system boot and when onlining memory in generic_online_page().
>
> generic_online_page() is used in two cases:
>
> 1. Direct memory onlining in online_pages().
> 2. Deferred memory onlining in memory-ballooning-like mechanisms (HyperV
> balloon and virtio-mem), when parts of a section are kept
> fake-offline to be fake-onlined later on.
>
> In 1, we already place pages to the tail of the freelist. Pages will be
> freed to MIGRATE_ISOLATE lists first and moved to the tail of the freelists
> via undo_isolate_page_range().
>
> In 2, we currently don't implement a proper rule. In case of virtio-mem,
> where we currently always online MAX_ORDER - 1 pages, the pages will be
> placed to the HEAD of the freelist - undesireable. While the hyper-v
> balloon calls generic_online_page() with single pages, usually it will
> call it on successive single pages in a larger block.
>
> The pages are fresh, so place them to the tail of the freelists and avoid
> the PCP. In __free_pages_core(), remove the now superflouos call to
> set_page_refcounted() and add a comment regarding page initialization and
> the refcount.
>
> Note: In 2. we currently don't shuffle. If ever relevant (page shuffling
> is usually of limited use in virtualized environments), we might want to
> shuffle after a sequence of generic_online_page() calls in the
> relevant callers.
>
> Reviewed-by: Vlastimil Babka <[email protected]>
> Reviewed-by: Oscar Salvador <[email protected]>
> Cc: Andrew Morton <[email protected]>
> Cc: Alexander Duyck <[email protected]>
> Cc: Mel Gorman <[email protected]>
> Cc: Michal Hocko <[email protected]>
> Cc: Dave Hansen <[email protected]>
> Cc: Vlastimil Babka <[email protected]>
> Cc: Wei Yang <[email protected]>
> Cc: Oscar Salvador <[email protected]>
> Cc: Mike Rapoport <[email protected]>
> Cc: "K. Y. Srinivasan" <[email protected]>
> Cc: Haiyang Zhang <[email protected]>
> Cc: Stephen Hemminger <[email protected]>
> Cc: Wei Liu <[email protected]>
> Signed-off-by: David Hildenbrand <[email protected]>
> ---
> mm/page_alloc.c | 37 ++++++++++++++++++++++++-------------
> 1 file changed, 24 insertions(+), 13 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index d5a5f528b8ca..8a2134fe9947 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -270,7 +270,8 @@ bool pm_suspended_storage(void)
> unsigned int pageblock_order __read_mostly;
> #endif
>
> -static void __free_pages_ok(struct page *page, unsigned int order);
> +static void __free_pages_ok(struct page *page, unsigned int order,
> + fop_t fop_flags);
>
> /*
> * results with 256, 32 in the lowmem_reserve sysctl:
> @@ -682,7 +683,7 @@ static void bad_page(struct page *page, const char *reason)
> void free_compound_page(struct page *page)
> {
> mem_cgroup_uncharge(page);
> - __free_pages_ok(page, compound_order(page));
> + __free_pages_ok(page, compound_order(page), FOP_NONE);
> }
>
> void prep_compound_page(struct page *page, unsigned int order)
> @@ -1419,17 +1420,15 @@ static void free_pcppages_bulk(struct zone *zone, int count,
> spin_unlock(&zone->lock);
> }
>
> -static void free_one_page(struct zone *zone,
> - struct page *page, unsigned long pfn,
> - unsigned int order,
> - int migratetype)
> +static void free_one_page(struct zone *zone, struct page *page, unsigned long pfn,
> + unsigned int order, int migratetype, fop_t fop_flags)
> {
> spin_lock(&zone->lock);
> if (unlikely(has_isolate_pageblock(zone) ||
> is_migrate_isolate(migratetype))) {
> migratetype = get_pfnblock_migratetype(page, pfn);
> }
> - __free_one_page(page, pfn, zone, order, migratetype, FOP_NONE);
> + __free_one_page(page, pfn, zone, order, migratetype, fop_flags);
> spin_unlock(&zone->lock);
> }
>
> @@ -1507,7 +1506,8 @@ void __meminit reserve_bootmem_region(phys_addr_t start, phys_addr_t end)
> }
> }
>
> -static void __free_pages_ok(struct page *page, unsigned int order)
> +static void __free_pages_ok(struct page *page, unsigned int order,
> + fop_t fop_flags)
> {
> unsigned long flags;
> int migratetype;
> @@ -1519,7 +1519,8 @@ static void __free_pages_ok(struct page *page, unsigned int order)
> migratetype = get_pfnblock_migratetype(page, pfn);
> local_irq_save(flags);
> __count_vm_events(PGFREE, 1 << order);
> - free_one_page(page_zone(page), page, pfn, order, migratetype);
> + free_one_page(page_zone(page), page, pfn, order, migratetype,
> + fop_flags);
> local_irq_restore(flags);
> }
>
> @@ -1529,6 +1530,11 @@ void __free_pages_core(struct page *page, unsigned int order)
> struct page *p = page;
> unsigned int loop;
>
> + /*
> + * When initializing the memmap, init_single_page() sets the refcount
> + * of all pages to 1 ("allocated"/"not free"). We have to set the
> + * refcount of all involved pages to 0.
> + */
> prefetchw(p);
> for (loop = 0; loop < (nr_pages - 1); loop++, p++) {
> prefetchw(p + 1);
> @@ -1539,8 +1545,12 @@ void __free_pages_core(struct page *page, unsigned int order)
> set_page_count(p, 0);
>
> atomic_long_add(nr_pages, &page_zone(page)->managed_pages);
> - set_page_refcounted(page);
> - __free_pages(page, order);
> +
> + /*
> + * Bypass PCP and place fresh pages right to the tail, primarily
> + * relevant for memory onlining.
> + */
> + __free_pages_ok(page, order, FOP_TO_TAIL);
> }
>
> #ifdef CONFIG_NEED_MULTIPLE_NODES
> @@ -3171,7 +3181,8 @@ static void free_unref_page_commit(struct page *page, unsigned long pfn)
> */
> if (migratetype >= MIGRATE_PCPTYPES) {
> if (unlikely(is_migrate_isolate(migratetype))) {
> - free_one_page(zone, page, pfn, 0, migratetype);
> + free_one_page(zone, page, pfn, 0, migratetype,
> + FOP_NONE);
> return;
> }
> migratetype = MIGRATE_MOVABLE;
> @@ -5063,7 +5074,7 @@ static inline void free_the_page(struct page *page, unsigned int order)
> if (order == 0) /* Via pcp? */
> free_unref_page(page);
> else
> - __free_pages_ok(page, order);
> + __free_pages_ok(page, order, FOP_NONE);
> }
>
> void __free_pages(struct page *page, unsigned int order)
Acked-by: Pankaj Gupta <[email protected]>
> __putback_isolated_page() already documents that pages will be placed to
> the tail of the freelist - this is, however, not the case for
> "order >= MAX_ORDER - 2" (see buddy_merge_likely()) - which should be
> the case for all existing users.
>
> This change affects two users:
> - free page reporting
> - page isolation, when undoing the isolation (including memory onlining).
>
> This behavior is desireable for pages that haven't really been touched
> lately, so exactly the two users that don't actually read/write page
> content, but rather move untouched pages.
>
> The new behavior is especially desirable for memory onlining, where we
> allow allocation of newly onlined pages via undo_isolate_page_range()
> in online_pages(). Right now, we always place them to the head of the
> free list, resulting in undesireable behavior: Assume we add
> individual memory chunks via add_memory() and online them right away to
> the NORMAL zone. We create a dependency chain of unmovable allocations
> e.g., via the memmap. The memmap of the next chunk will be placed onto
> previous chunks - if the last block cannot get offlined+removed, all
> dependent ones cannot get offlined+removed. While this can already be
> observed with individual DIMMs, it's more of an issue for virtio-mem
> (and I suspect also ppc DLPAR).
>
> Document that this should only be used for optimizations, and no code
> should realy on this for correction (if the order of freepage lists
> ever changes).
>
> We won't care about page shuffling: memory onlining already properly
> shuffles after onlining. free page reporting doesn't care about
> physically contiguous ranges, and there are already cases where page
> isolation will simply move (physically close) free pages to (currently)
> the head of the freelists via move_freepages_block() instead of
> shuffling. If this becomes ever relevant, we should shuffle the whole
> zone when undoing isolation of larger ranges, and after
> free_contig_range().
>
> Reviewed-by: Alexander Duyck <[email protected]>
> Reviewed-by: Oscar Salvador <[email protected]>
> Cc: Andrew Morton <[email protected]>
> Cc: Alexander Duyck <[email protected]>
> Cc: Mel Gorman <[email protected]>
> Cc: Michal Hocko <[email protected]>
> Cc: Dave Hansen <[email protected]>
> Cc: Vlastimil Babka <[email protected]>
> Cc: Wei Yang <[email protected]>
> Cc: Oscar Salvador <[email protected]>
> Cc: Mike Rapoport <[email protected]>
> Cc: Scott Cheloha <[email protected]>
> Cc: Michael Ellerman <[email protected]>
> Signed-off-by: David Hildenbrand <[email protected]>
> ---
> mm/page_alloc.c | 18 ++++++++++++++++--
> 1 file changed, 16 insertions(+), 2 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index daab90e960fe..9e3ed4a6f69a 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -89,6 +89,18 @@ typedef int __bitwise fop_t;
> */
> #define FOP_SKIP_REPORT_NOTIFY ((__force fop_t)BIT(0))
>
> +/*
> + * Place the (possibly merged) page to the tail of the freelist. Will ignore
> + * page shuffling (relevant code - e.g., memory onlining - is expected to
> + * shuffle the whole zone).
> + *
> + * Note: No code should rely onto this flag for correctness - it's purely
> + * to allow for optimizations when handing back either fresh pages
> + * (memory onlining) or untouched pages (page isolation, free page
> + * reporting).
> + */
> +#define FOP_TO_TAIL ((__force fop_t)BIT(1))
> +
> /* prevent >1 _updater_ of zone percpu pageset ->high and ->batch fields */
> static DEFINE_MUTEX(pcp_batch_high_lock);
> #define MIN_PERCPU_PAGELIST_FRACTION (8)
> @@ -1038,7 +1050,9 @@ static inline void __free_one_page(struct page *page, unsigned long pfn,
> done_merging:
> set_page_order(page, order);
>
> - if (is_shuffle_order(order))
> + if (fop_flags & FOP_TO_TAIL)
> + to_tail = true;
> + else if (is_shuffle_order(order))
> to_tail = shuffle_pick_tail();
> else
> to_tail = buddy_merge_likely(pfn, buddy_pfn, page, order);
> @@ -3300,7 +3314,7 @@ void __putback_isolated_page(struct page *page, unsigned int order, int mt)
>
> /* Return isolated page to tail of freelist. */
> __free_one_page(page, page_to_pfn(page), zone, order, mt,
> - FOP_SKIP_REPORT_NOTIFY);
> + FOP_SKIP_REPORT_NOTIFY | FOP_TO_TAIL);
> }
Reviewed-by: Pankaj Gupta <[email protected]>
> Page isolation doesn't actually touch the pages, it simply isolates
> pageblocks and moves all free pages to the MIGRATE_ISOLATE freelist.
>
> We already place pages to the tail of the freelists when undoing
> isolation via __putback_isolated_page(), let's do it in any case
> (e.g., if order <= pageblock_order) and document the behavior.
>
> Add a "to_tail" parameter to move_freepages_block() but introduce a
> a new move_to_free_list_tail() - similar to add_to_free_list_tail().
>
> This change results in all pages getting onlined via online_pages() to
> be placed to the tail of the freelist.
>
> Reviewed-by: Oscar Salvador <[email protected]>
> Cc: Andrew Morton <[email protected]>
> Cc: Alexander Duyck <[email protected]>
> Cc: Mel Gorman <[email protected]>
> Cc: Michal Hocko <[email protected]>
> Cc: Dave Hansen <[email protected]>
> Cc: Vlastimil Babka <[email protected]>
> Cc: Wei Yang <[email protected]>
> Cc: Oscar Salvador <[email protected]>
> Cc: Mike Rapoport <[email protected]>
> Cc: Scott Cheloha <[email protected]>
> Cc: Michael Ellerman <[email protected]>
> Signed-off-by: David Hildenbrand <[email protected]>
> ---
> include/linux/page-isolation.h | 4 ++--
> mm/page_alloc.c | 35 +++++++++++++++++++++++-----------
> mm/page_isolation.c | 12 +++++++++---
> 3 files changed, 35 insertions(+), 16 deletions(-)
>
> diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h
> index 572458016331..3eca9b3c5305 100644
> --- a/include/linux/page-isolation.h
> +++ b/include/linux/page-isolation.h
> @@ -36,8 +36,8 @@ static inline bool is_migrate_isolate(int migratetype)
> struct page *has_unmovable_pages(struct zone *zone, struct page *page,
> int migratetype, int flags);
> void set_pageblock_migratetype(struct page *page, int migratetype);
> -int move_freepages_block(struct zone *zone, struct page *page,
> - int migratetype, int *num_movable);
> +int move_freepages_block(struct zone *zone, struct page *page, int migratetype,
> + bool to_tail, int *num_movable);
>
> /*
> * Changes migrate type in [start_pfn, end_pfn) to be MIGRATE_ISOLATE.
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 9e3ed4a6f69a..d5a5f528b8ca 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -905,6 +905,15 @@ static inline void move_to_free_list(struct page *page, struct zone *zone,
> list_move(&page->lru, &area->free_list[migratetype]);
> }
>
> +/* Used for pages which are on another list */
> +static inline void move_to_free_list_tail(struct page *page, struct zone *zone,
> + unsigned int order, int migratetype)
> +{
> + struct free_area *area = &zone->free_area[order];
> +
> + list_move_tail(&page->lru, &area->free_list[migratetype]);
> +}
> +
> static inline void del_page_from_free_list(struct page *page, struct zone *zone,
> unsigned int order)
> {
> @@ -2338,9 +2347,9 @@ static inline struct page *__rmqueue_cma_fallback(struct zone *zone,
> * Note that start_page and end_pages are not aligned on a pageblock
> * boundary. If alignment is required, use move_freepages_block()
> */
> -static int move_freepages(struct zone *zone,
> - struct page *start_page, struct page *end_page,
> - int migratetype, int *num_movable)
> +static int move_freepages(struct zone *zone, struct page *start_page,
> + struct page *end_page, int migratetype,
> + bool to_tail, int *num_movable)
> {
> struct page *page;
> unsigned int order;
> @@ -2371,7 +2380,10 @@ static int move_freepages(struct zone *zone,
> VM_BUG_ON_PAGE(page_zone(page) != zone, page);
>
> order = page_order(page);
> - move_to_free_list(page, zone, order, migratetype);
> + if (to_tail)
> + move_to_free_list_tail(page, zone, order, migratetype);
> + else
> + move_to_free_list(page, zone, order, migratetype);
> page += 1 << order;
> pages_moved += 1 << order;
> }
> @@ -2379,8 +2391,8 @@ static int move_freepages(struct zone *zone,
> return pages_moved;
> }
>
> -int move_freepages_block(struct zone *zone, struct page *page,
> - int migratetype, int *num_movable)
> +int move_freepages_block(struct zone *zone, struct page *page, int migratetype,
> + bool to_tail, int *num_movable)
> {
> unsigned long start_pfn, end_pfn;
> struct page *start_page, *end_page;
> @@ -2401,7 +2413,7 @@ int move_freepages_block(struct zone *zone, struct page *page,
> return 0;
>
> return move_freepages(zone, start_page, end_page, migratetype,
> - num_movable);
> + to_tail, num_movable);
> }
>
> static void change_pageblock_range(struct page *pageblock_page,
> @@ -2526,8 +2538,8 @@ static void steal_suitable_fallback(struct zone *zone, struct page *page,
> if (!whole_block)
> goto single_page;
>
> - free_pages = move_freepages_block(zone, page, start_type,
> - &movable_pages);
> + free_pages = move_freepages_block(zone, page, start_type, false,
> + &movable_pages);
> /*
> * Determine how many pages are compatible with our allocation.
> * For movable allocation, it's the number of movable pages which
> @@ -2635,7 +2647,8 @@ static void reserve_highatomic_pageblock(struct page *page, struct zone *zone,
> && !is_migrate_cma(mt)) {
> zone->nr_reserved_highatomic += pageblock_nr_pages;
> set_pageblock_migratetype(page, MIGRATE_HIGHATOMIC);
> - move_freepages_block(zone, page, MIGRATE_HIGHATOMIC, NULL);
> + move_freepages_block(zone, page, MIGRATE_HIGHATOMIC, false,
> + NULL);
> }
>
> out_unlock:
> @@ -2711,7 +2724,7 @@ static bool unreserve_highatomic_pageblock(const struct alloc_context *ac,
> */
> set_pageblock_migratetype(page, ac->migratetype);
> ret = move_freepages_block(zone, page, ac->migratetype,
> - NULL);
> + false, NULL);
> if (ret) {
> spin_unlock_irqrestore(&zone->lock, flags);
> return ret;
> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> index abfe26ad59fd..de44e1329706 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -45,7 +45,7 @@ static int set_migratetype_isolate(struct page *page, int migratetype, int isol_
> set_pageblock_migratetype(page, MIGRATE_ISOLATE);
> zone->nr_isolate_pageblock++;
> nr_pages = move_freepages_block(zone, page, MIGRATE_ISOLATE,
> - NULL);
> + false, NULL);
>
> __mod_zone_freepage_state(zone, -nr_pages, mt);
> spin_unlock_irqrestore(&zone->lock, flags);
> @@ -83,7 +83,7 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype)
> * Because freepage with more than pageblock_order on isolated
> * pageblock is restricted to merge due to freepage counting problem,
> * it is possible that there is free buddy page.
> - * move_freepages_block() doesn't care of merge so we need other
> + * move_freepages_block() don't care about merging, so we need another
> * approach in order to merge them. Isolation and free will make
> * these pages to be merged.
> */
> @@ -106,9 +106,15 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype)
> * If we isolate freepage with more than pageblock_order, there
> * should be no freepage in the range, so we could avoid costly
> * pageblock scanning for freepage moving.
> + *
> + * We didn't actually touch any of the isolated pages, so place them
> + * to the tail of the freelist. This is an optimization for memory
> + * onlining - just onlined memory won't immediately be considered for
> + * allocation.
> */
> if (!isolated_page) {
> - nr_pages = move_freepages_block(zone, page, migratetype, NULL);
> + nr_pages = move_freepages_block(zone, page, migratetype, true,
> + NULL);
> __mod_zone_freepage_state(zone, nr_pages, migratetype);
> }
> set_pageblock_migratetype(page, migratetype);
Acked-by: Pankaj Gupta <[email protected]>
On Mon, Sep 28, 2020 at 08:21:06PM +0200, David Hildenbrand wrote:
>Let's prepare for additional flags and avoid long parameter lists of bools.
>Follow-up patches will also make use of the flags in __free_pages_ok(),
>however, I wasn't able to come up with a better name for the type - should
>be good enough for internal purposes.
>
>Reviewed-by: Alexander Duyck <[email protected]>
>Reviewed-by: Vlastimil Babka <[email protected]>
>Reviewed-by: Oscar Salvador <[email protected]>
>Cc: Andrew Morton <[email protected]>
>Cc: Alexander Duyck <[email protected]>
>Cc: Mel Gorman <[email protected]>
>Cc: Michal Hocko <[email protected]>
>Cc: Dave Hansen <[email protected]>
>Cc: Vlastimil Babka <[email protected]>
>Cc: Wei Yang <[email protected]>
>Cc: Oscar Salvador <[email protected]>
>Cc: Mike Rapoport <[email protected]>
>Signed-off-by: David Hildenbrand <[email protected]>
Reviewed-by: Wei Yang <[email protected]>
>---
> mm/page_alloc.c | 28 ++++++++++++++++++++--------
> 1 file changed, 20 insertions(+), 8 deletions(-)
>
>diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>index df90e3654f97..daab90e960fe 100644
>--- a/mm/page_alloc.c
>+++ b/mm/page_alloc.c
>@@ -77,6 +77,18 @@
> #include "shuffle.h"
> #include "page_reporting.h"
>
>+/* Free One Page flags: for internal, non-pcp variants of free_pages(). */
>+typedef int __bitwise fop_t;
>+
>+/* No special request */
>+#define FOP_NONE ((__force fop_t)0)
>+
>+/*
>+ * Skip free page reporting notification for the (possibly merged) page. (will
>+ * *not* mark the page reported, only skip the notification).
>+ */
>+#define FOP_SKIP_REPORT_NOTIFY ((__force fop_t)BIT(0))
>+
> /* prevent >1 _updater_ of zone percpu pageset ->high and ->batch fields */
> static DEFINE_MUTEX(pcp_batch_high_lock);
> #define MIN_PERCPU_PAGELIST_FRACTION (8)
>@@ -948,10 +960,9 @@ buddy_merge_likely(unsigned long pfn, unsigned long buddy_pfn,
> * -- nyc
> */
>
>-static inline void __free_one_page(struct page *page,
>- unsigned long pfn,
>- struct zone *zone, unsigned int order,
>- int migratetype, bool report)
>+static inline void __free_one_page(struct page *page, unsigned long pfn,
>+ struct zone *zone, unsigned int order,
>+ int migratetype, fop_t fop_flags)
> {
> struct capture_control *capc = task_capc(zone);
> unsigned long buddy_pfn;
>@@ -1038,7 +1049,7 @@ static inline void __free_one_page(struct page *page,
> add_to_free_list(page, zone, order, migratetype);
>
> /* Notify page reporting subsystem of freed page */
>- if (report)
>+ if (!(fop_flags & FOP_SKIP_REPORT_NOTIFY))
> page_reporting_notify_free(order);
> }
>
>@@ -1379,7 +1390,7 @@ static void free_pcppages_bulk(struct zone *zone, int count,
> if (unlikely(isolated_pageblocks))
> mt = get_pageblock_migratetype(page);
>
>- __free_one_page(page, page_to_pfn(page), zone, 0, mt, true);
>+ __free_one_page(page, page_to_pfn(page), zone, 0, mt, FOP_NONE);
> trace_mm_page_pcpu_drain(page, 0, mt);
> }
> spin_unlock(&zone->lock);
>@@ -1395,7 +1406,7 @@ static void free_one_page(struct zone *zone,
> is_migrate_isolate(migratetype))) {
> migratetype = get_pfnblock_migratetype(page, pfn);
> }
>- __free_one_page(page, pfn, zone, order, migratetype, true);
>+ __free_one_page(page, pfn, zone, order, migratetype, FOP_NONE);
> spin_unlock(&zone->lock);
> }
>
>@@ -3288,7 +3299,8 @@ void __putback_isolated_page(struct page *page, unsigned int order, int mt)
> lockdep_assert_held(&zone->lock);
>
> /* Return isolated page to tail of freelist. */
>- __free_one_page(page, page_to_pfn(page), zone, order, mt, false);
>+ __free_one_page(page, page_to_pfn(page), zone, order, mt,
>+ FOP_SKIP_REPORT_NOTIFY);
> }
>
> /*
>--
>2.26.2
--
Wei Yang
Help you, Help me
On Mon, Sep 28, 2020 at 08:21:07PM +0200, David Hildenbrand wrote:
>__putback_isolated_page() already documents that pages will be placed to
>the tail of the freelist - this is, however, not the case for
>"order >= MAX_ORDER - 2" (see buddy_merge_likely()) - which should be
>the case for all existing users.
>
>This change affects two users:
>- free page reporting
>- page isolation, when undoing the isolation (including memory onlining).
>
>This behavior is desireable for pages that haven't really been touched
>lately, so exactly the two users that don't actually read/write page
>content, but rather move untouched pages.
>
>The new behavior is especially desirable for memory onlining, where we
>allow allocation of newly onlined pages via undo_isolate_page_range()
>in online_pages(). Right now, we always place them to the head of the
>free list, resulting in undesireable behavior: Assume we add
>individual memory chunks via add_memory() and online them right away to
>the NORMAL zone. We create a dependency chain of unmovable allocations
>e.g., via the memmap. The memmap of the next chunk will be placed onto
>previous chunks - if the last block cannot get offlined+removed, all
>dependent ones cannot get offlined+removed. While this can already be
>observed with individual DIMMs, it's more of an issue for virtio-mem
>(and I suspect also ppc DLPAR).
>
>Document that this should only be used for optimizations, and no code
>should realy on this for correction (if the order of freepage lists
>ever changes).
>
>We won't care about page shuffling: memory onlining already properly
>shuffles after onlining. free page reporting doesn't care about
>physically contiguous ranges, and there are already cases where page
>isolation will simply move (physically close) free pages to (currently)
>the head of the freelists via move_freepages_block() instead of
>shuffling. If this becomes ever relevant, we should shuffle the whole
>zone when undoing isolation of larger ranges, and after
>free_contig_range().
>
>Reviewed-by: Alexander Duyck <[email protected]>
>Reviewed-by: Oscar Salvador <[email protected]>
>Cc: Andrew Morton <[email protected]>
>Cc: Alexander Duyck <[email protected]>
>Cc: Mel Gorman <[email protected]>
>Cc: Michal Hocko <[email protected]>
>Cc: Dave Hansen <[email protected]>
>Cc: Vlastimil Babka <[email protected]>
>Cc: Wei Yang <[email protected]>
>Cc: Oscar Salvador <[email protected]>
>Cc: Mike Rapoport <[email protected]>
>Cc: Scott Cheloha <[email protected]>
>Cc: Michael Ellerman <[email protected]>
>Signed-off-by: David Hildenbrand <[email protected]>
Reviewed-by: Wei Yang <[email protected]>
>---
> mm/page_alloc.c | 18 ++++++++++++++++--
> 1 file changed, 16 insertions(+), 2 deletions(-)
>
>diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>index daab90e960fe..9e3ed4a6f69a 100644
>--- a/mm/page_alloc.c
>+++ b/mm/page_alloc.c
>@@ -89,6 +89,18 @@ typedef int __bitwise fop_t;
> */
> #define FOP_SKIP_REPORT_NOTIFY ((__force fop_t)BIT(0))
>
>+/*
>+ * Place the (possibly merged) page to the tail of the freelist. Will ignore
>+ * page shuffling (relevant code - e.g., memory onlining - is expected to
>+ * shuffle the whole zone).
>+ *
>+ * Note: No code should rely onto this flag for correctness - it's purely
>+ * to allow for optimizations when handing back either fresh pages
>+ * (memory onlining) or untouched pages (page isolation, free page
>+ * reporting).
>+ */
>+#define FOP_TO_TAIL ((__force fop_t)BIT(1))
>+
> /* prevent >1 _updater_ of zone percpu pageset ->high and ->batch fields */
> static DEFINE_MUTEX(pcp_batch_high_lock);
> #define MIN_PERCPU_PAGELIST_FRACTION (8)
>@@ -1038,7 +1050,9 @@ static inline void __free_one_page(struct page *page, unsigned long pfn,
> done_merging:
> set_page_order(page, order);
>
>- if (is_shuffle_order(order))
>+ if (fop_flags & FOP_TO_TAIL)
>+ to_tail = true;
>+ else if (is_shuffle_order(order))
> to_tail = shuffle_pick_tail();
> else
> to_tail = buddy_merge_likely(pfn, buddy_pfn, page, order);
>@@ -3300,7 +3314,7 @@ void __putback_isolated_page(struct page *page, unsigned int order, int mt)
>
> /* Return isolated page to tail of freelist. */
> __free_one_page(page, page_to_pfn(page), zone, order, mt,
>- FOP_SKIP_REPORT_NOTIFY);
>+ FOP_SKIP_REPORT_NOTIFY | FOP_TO_TAIL);
> }
>
> /*
>--
>2.26.2
--
Wei Yang
Help you, Help me
On Mon, Sep 28, 2020 at 08:21:08PM +0200, David Hildenbrand wrote:
>Page isolation doesn't actually touch the pages, it simply isolates
>pageblocks and moves all free pages to the MIGRATE_ISOLATE freelist.
>
>We already place pages to the tail of the freelists when undoing
>isolation via __putback_isolated_page(), let's do it in any case
>(e.g., if order <= pageblock_order) and document the behavior.
>
>Add a "to_tail" parameter to move_freepages_block() but introduce a
>a new move_to_free_list_tail() - similar to add_to_free_list_tail().
>
>This change results in all pages getting onlined via online_pages() to
>be placed to the tail of the freelist.
>
>Reviewed-by: Oscar Salvador <[email protected]>
>Cc: Andrew Morton <[email protected]>
>Cc: Alexander Duyck <[email protected]>
>Cc: Mel Gorman <[email protected]>
>Cc: Michal Hocko <[email protected]>
>Cc: Dave Hansen <[email protected]>
>Cc: Vlastimil Babka <[email protected]>
>Cc: Wei Yang <[email protected]>
>Cc: Oscar Salvador <[email protected]>
>Cc: Mike Rapoport <[email protected]>
>Cc: Scott Cheloha <[email protected]>
>Cc: Michael Ellerman <[email protected]>
>Signed-off-by: David Hildenbrand <[email protected]>
>---
> include/linux/page-isolation.h | 4 ++--
> mm/page_alloc.c | 35 +++++++++++++++++++++++-----------
> mm/page_isolation.c | 12 +++++++++---
> 3 files changed, 35 insertions(+), 16 deletions(-)
>
>diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h
>index 572458016331..3eca9b3c5305 100644
>--- a/include/linux/page-isolation.h
>+++ b/include/linux/page-isolation.h
>@@ -36,8 +36,8 @@ static inline bool is_migrate_isolate(int migratetype)
> struct page *has_unmovable_pages(struct zone *zone, struct page *page,
> int migratetype, int flags);
> void set_pageblock_migratetype(struct page *page, int migratetype);
>-int move_freepages_block(struct zone *zone, struct page *page,
>- int migratetype, int *num_movable);
>+int move_freepages_block(struct zone *zone, struct page *page, int migratetype,
>+ bool to_tail, int *num_movable);
>
> /*
> * Changes migrate type in [start_pfn, end_pfn) to be MIGRATE_ISOLATE.
>diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>index 9e3ed4a6f69a..d5a5f528b8ca 100644
>--- a/mm/page_alloc.c
>+++ b/mm/page_alloc.c
>@@ -905,6 +905,15 @@ static inline void move_to_free_list(struct page *page, struct zone *zone,
> list_move(&page->lru, &area->free_list[migratetype]);
> }
>
>+/* Used for pages which are on another list */
>+static inline void move_to_free_list_tail(struct page *page, struct zone *zone,
>+ unsigned int order, int migratetype)
>+{
>+ struct free_area *area = &zone->free_area[order];
>+
>+ list_move_tail(&page->lru, &area->free_list[migratetype]);
>+}
>+
Would it be better to pass the *to_tail* to move_to_free_list(), so we won't
have a new function?
> static inline void del_page_from_free_list(struct page *page, struct zone *zone,
> unsigned int order)
> {
>@@ -2338,9 +2347,9 @@ static inline struct page *__rmqueue_cma_fallback(struct zone *zone,
> * Note that start_page and end_pages are not aligned on a pageblock
> * boundary. If alignment is required, use move_freepages_block()
> */
>-static int move_freepages(struct zone *zone,
>- struct page *start_page, struct page *end_page,
>- int migratetype, int *num_movable)
>+static int move_freepages(struct zone *zone, struct page *start_page,
>+ struct page *end_page, int migratetype,
>+ bool to_tail, int *num_movable)
> {
> struct page *page;
> unsigned int order;
>@@ -2371,7 +2380,10 @@ static int move_freepages(struct zone *zone,
> VM_BUG_ON_PAGE(page_zone(page) != zone, page);
>
> order = page_order(page);
>- move_to_free_list(page, zone, order, migratetype);
>+ if (to_tail)
>+ move_to_free_list_tail(page, zone, order, migratetype);
>+ else
>+ move_to_free_list(page, zone, order, migratetype);
And here, we just need to pass the *to_tail* to move_to_free_list().
> page += 1 << order;
> pages_moved += 1 << order;
> }
>@@ -2379,8 +2391,8 @@ static int move_freepages(struct zone *zone,
> return pages_moved;
> }
>
>-int move_freepages_block(struct zone *zone, struct page *page,
>- int migratetype, int *num_movable)
>+int move_freepages_block(struct zone *zone, struct page *page, int migratetype,
>+ bool to_tail, int *num_movable)
> {
> unsigned long start_pfn, end_pfn;
> struct page *start_page, *end_page;
>@@ -2401,7 +2413,7 @@ int move_freepages_block(struct zone *zone, struct page *page,
> return 0;
>
> return move_freepages(zone, start_page, end_page, migratetype,
>- num_movable);
>+ to_tail, num_movable);
> }
>
> static void change_pageblock_range(struct page *pageblock_page,
>@@ -2526,8 +2538,8 @@ static void steal_suitable_fallback(struct zone *zone, struct page *page,
> if (!whole_block)
> goto single_page;
>
>- free_pages = move_freepages_block(zone, page, start_type,
>- &movable_pages);
>+ free_pages = move_freepages_block(zone, page, start_type, false,
>+ &movable_pages);
> /*
> * Determine how many pages are compatible with our allocation.
> * For movable allocation, it's the number of movable pages which
>@@ -2635,7 +2647,8 @@ static void reserve_highatomic_pageblock(struct page *page, struct zone *zone,
> && !is_migrate_cma(mt)) {
> zone->nr_reserved_highatomic += pageblock_nr_pages;
> set_pageblock_migratetype(page, MIGRATE_HIGHATOMIC);
>- move_freepages_block(zone, page, MIGRATE_HIGHATOMIC, NULL);
>+ move_freepages_block(zone, page, MIGRATE_HIGHATOMIC, false,
>+ NULL);
> }
>
> out_unlock:
>@@ -2711,7 +2724,7 @@ static bool unreserve_highatomic_pageblock(const struct alloc_context *ac,
> */
> set_pageblock_migratetype(page, ac->migratetype);
> ret = move_freepages_block(zone, page, ac->migratetype,
>- NULL);
>+ false, NULL);
> if (ret) {
> spin_unlock_irqrestore(&zone->lock, flags);
> return ret;
>diff --git a/mm/page_isolation.c b/mm/page_isolation.c
>index abfe26ad59fd..de44e1329706 100644
>--- a/mm/page_isolation.c
>+++ b/mm/page_isolation.c
>@@ -45,7 +45,7 @@ static int set_migratetype_isolate(struct page *page, int migratetype, int isol_
> set_pageblock_migratetype(page, MIGRATE_ISOLATE);
> zone->nr_isolate_pageblock++;
> nr_pages = move_freepages_block(zone, page, MIGRATE_ISOLATE,
>- NULL);
>+ false, NULL);
>
> __mod_zone_freepage_state(zone, -nr_pages, mt);
> spin_unlock_irqrestore(&zone->lock, flags);
>@@ -83,7 +83,7 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype)
> * Because freepage with more than pageblock_order on isolated
> * pageblock is restricted to merge due to freepage counting problem,
> * it is possible that there is free buddy page.
>- * move_freepages_block() doesn't care of merge so we need other
>+ * move_freepages_block() don't care about merging, so we need another
> * approach in order to merge them. Isolation and free will make
> * these pages to be merged.
> */
>@@ -106,9 +106,15 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype)
> * If we isolate freepage with more than pageblock_order, there
> * should be no freepage in the range, so we could avoid costly
> * pageblock scanning for freepage moving.
>+ *
>+ * We didn't actually touch any of the isolated pages, so place them
>+ * to the tail of the freelist. This is an optimization for memory
>+ * onlining - just onlined memory won't immediately be considered for
>+ * allocation.
> */
> if (!isolated_page) {
>- nr_pages = move_freepages_block(zone, page, migratetype, NULL);
>+ nr_pages = move_freepages_block(zone, page, migratetype, true,
>+ NULL);
> __mod_zone_freepage_state(zone, nr_pages, migratetype);
> }
> set_pageblock_migratetype(page, migratetype);
>--
>2.26.2
Others looks good to me.
--
Wei Yang
Help you, Help me
On Mon, Sep 28, 2020 at 08:21:09PM +0200, David Hildenbrand wrote:
>__free_pages_core() is used when exposing fresh memory to the buddy
>during system boot and when onlining memory in generic_online_page().
>
>generic_online_page() is used in two cases:
>
>1. Direct memory onlining in online_pages().
>2. Deferred memory onlining in memory-ballooning-like mechanisms (HyperV
> balloon and virtio-mem), when parts of a section are kept
> fake-offline to be fake-onlined later on.
>
>In 1, we already place pages to the tail of the freelist. Pages will be
>freed to MIGRATE_ISOLATE lists first and moved to the tail of the freelists
>via undo_isolate_page_range().
>
>In 2, we currently don't implement a proper rule. In case of virtio-mem,
>where we currently always online MAX_ORDER - 1 pages, the pages will be
>placed to the HEAD of the freelist - undesireable. While the hyper-v
>balloon calls generic_online_page() with single pages, usually it will
>call it on successive single pages in a larger block.
>
>The pages are fresh, so place them to the tail of the freelists and avoid
>the PCP. In __free_pages_core(), remove the now superflouos call to
>set_page_refcounted() and add a comment regarding page initialization and
>the refcount.
>
>Note: In 2. we currently don't shuffle. If ever relevant (page shuffling
>is usually of limited use in virtualized environments), we might want to
>shuffle after a sequence of generic_online_page() calls in the
>relevant callers.
>
>Reviewed-by: Vlastimil Babka <[email protected]>
>Reviewed-by: Oscar Salvador <[email protected]>
>Cc: Andrew Morton <[email protected]>
>Cc: Alexander Duyck <[email protected]>
>Cc: Mel Gorman <[email protected]>
>Cc: Michal Hocko <[email protected]>
>Cc: Dave Hansen <[email protected]>
>Cc: Vlastimil Babka <[email protected]>
>Cc: Wei Yang <[email protected]>
>Cc: Oscar Salvador <[email protected]>
>Cc: Mike Rapoport <[email protected]>
>Cc: "K. Y. Srinivasan" <[email protected]>
>Cc: Haiyang Zhang <[email protected]>
>Cc: Stephen Hemminger <[email protected]>
>Cc: Wei Liu <[email protected]>
>Signed-off-by: David Hildenbrand <[email protected]>
>---
> mm/page_alloc.c | 37 ++++++++++++++++++++++++-------------
> 1 file changed, 24 insertions(+), 13 deletions(-)
>
>diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>index d5a5f528b8ca..8a2134fe9947 100644
>--- a/mm/page_alloc.c
>+++ b/mm/page_alloc.c
>@@ -270,7 +270,8 @@ bool pm_suspended_storage(void)
> unsigned int pageblock_order __read_mostly;
> #endif
>
>-static void __free_pages_ok(struct page *page, unsigned int order);
>+static void __free_pages_ok(struct page *page, unsigned int order,
>+ fop_t fop_flags);
>
> /*
> * results with 256, 32 in the lowmem_reserve sysctl:
>@@ -682,7 +683,7 @@ static void bad_page(struct page *page, const char *reason)
> void free_compound_page(struct page *page)
> {
> mem_cgroup_uncharge(page);
>- __free_pages_ok(page, compound_order(page));
>+ __free_pages_ok(page, compound_order(page), FOP_NONE);
> }
>
> void prep_compound_page(struct page *page, unsigned int order)
>@@ -1419,17 +1420,15 @@ static void free_pcppages_bulk(struct zone *zone, int count,
> spin_unlock(&zone->lock);
> }
>
>-static void free_one_page(struct zone *zone,
>- struct page *page, unsigned long pfn,
>- unsigned int order,
>- int migratetype)
>+static void free_one_page(struct zone *zone, struct page *page, unsigned long pfn,
>+ unsigned int order, int migratetype, fop_t fop_flags)
> {
> spin_lock(&zone->lock);
> if (unlikely(has_isolate_pageblock(zone) ||
> is_migrate_isolate(migratetype))) {
> migratetype = get_pfnblock_migratetype(page, pfn);
> }
>- __free_one_page(page, pfn, zone, order, migratetype, FOP_NONE);
>+ __free_one_page(page, pfn, zone, order, migratetype, fop_flags);
> spin_unlock(&zone->lock);
> }
>
>@@ -1507,7 +1506,8 @@ void __meminit reserve_bootmem_region(phys_addr_t start, phys_addr_t end)
> }
> }
>
>-static void __free_pages_ok(struct page *page, unsigned int order)
>+static void __free_pages_ok(struct page *page, unsigned int order,
>+ fop_t fop_flags)
> {
> unsigned long flags;
> int migratetype;
>@@ -1519,7 +1519,8 @@ static void __free_pages_ok(struct page *page, unsigned int order)
> migratetype = get_pfnblock_migratetype(page, pfn);
> local_irq_save(flags);
> __count_vm_events(PGFREE, 1 << order);
>- free_one_page(page_zone(page), page, pfn, order, migratetype);
>+ free_one_page(page_zone(page), page, pfn, order, migratetype,
>+ fop_flags);
> local_irq_restore(flags);
> }
>
>@@ -1529,6 +1530,11 @@ void __free_pages_core(struct page *page, unsigned int order)
> struct page *p = page;
> unsigned int loop;
>
>+ /*
>+ * When initializing the memmap, init_single_page() sets the refcount
If my code is the latest version.
s/init_single_page/__init_single_page/
Besides this.
Reviewed-by: Wei Yang <[email protected]>
>+ * of all pages to 1 ("allocated"/"not free"). We have to set the
>+ * refcount of all involved pages to 0.
>+ */
> prefetchw(p);
> for (loop = 0; loop < (nr_pages - 1); loop++, p++) {
> prefetchw(p + 1);
>@@ -1539,8 +1545,12 @@ void __free_pages_core(struct page *page, unsigned int order)
> set_page_count(p, 0);
>
> atomic_long_add(nr_pages, &page_zone(page)->managed_pages);
>- set_page_refcounted(page);
>- __free_pages(page, order);
>+
>+ /*
>+ * Bypass PCP and place fresh pages right to the tail, primarily
>+ * relevant for memory onlining.
>+ */
>+ __free_pages_ok(page, order, FOP_TO_TAIL);
> }
>
> #ifdef CONFIG_NEED_MULTIPLE_NODES
>@@ -3171,7 +3181,8 @@ static void free_unref_page_commit(struct page *page, unsigned long pfn)
> */
> if (migratetype >= MIGRATE_PCPTYPES) {
> if (unlikely(is_migrate_isolate(migratetype))) {
>- free_one_page(zone, page, pfn, 0, migratetype);
>+ free_one_page(zone, page, pfn, 0, migratetype,
>+ FOP_NONE);
> return;
> }
> migratetype = MIGRATE_MOVABLE;
>@@ -5063,7 +5074,7 @@ static inline void free_the_page(struct page *page, unsigned int order)
> if (order == 0) /* Via pcp? */
> free_unref_page(page);
> else
>- __free_pages_ok(page, order);
>+ __free_pages_ok(page, order, FOP_NONE);
> }
>
> void __free_pages(struct page *page, unsigned int order)
>--
>2.26.2
--
Wei Yang
Help you, Help me
On Mon, Sep 28, 2020 at 08:21:10PM +0200, David Hildenbrand wrote:
>As we no longer shuffle via generic_online_page() and when undoing
>isolation, we can simplify the comment.
>
>We now effectively shuffle only once (properly) when onlining new
>memory.
>
>Cc: Andrew Morton <[email protected]>
>Cc: Alexander Duyck <[email protected]>
>Cc: Mel Gorman <[email protected]>
>Cc: Michal Hocko <[email protected]>
>Cc: Dave Hansen <[email protected]>
>Cc: Vlastimil Babka <[email protected]>
>Cc: Wei Yang <[email protected]>
>Cc: Oscar Salvador <[email protected]>
>Cc: Mike Rapoport <[email protected]>
>Signed-off-by: David Hildenbrand <[email protected]>
Reviewed-by: Wei Yang <[email protected]>
>---
> mm/memory_hotplug.c | 11 ++++-------
> 1 file changed, 4 insertions(+), 7 deletions(-)
>
>diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>index 9db80ee29caa..c589bd8801bb 100644
>--- a/mm/memory_hotplug.c
>+++ b/mm/memory_hotplug.c
>@@ -859,13 +859,10 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
> undo_isolate_page_range(pfn, pfn + nr_pages, MIGRATE_MOVABLE);
>
> /*
>- * When exposing larger, physically contiguous memory areas to the
>- * buddy, shuffling in the buddy (when freeing onlined pages, putting
>- * them either to the head or the tail of the freelist) is only helpful
>- * for maintaining the shuffle, but not for creating the initial
>- * shuffle. Shuffle the whole zone to make sure the just onlined pages
>- * are properly distributed across the whole freelist. Make sure to
>- * shuffle once pageblocks are no longer isolated.
>+ * Freshly onlined pages aren't shuffled (e.g., all pages are placed to
>+ * the tail of the freelist when undoing isolation). Shuffle the whole
>+ * zone to make sure the just onlined pages are properly distributed
>+ * across the whole freelist - to create an initial shuffle.
> */
> shuffle_zone(zone);
>
>--
>2.26.2
--
Wei Yang
Help you, Help me
On 29.09.20 11:18, Wei Yang wrote:
> On Mon, Sep 28, 2020 at 08:21:08PM +0200, David Hildenbrand wrote:
>> Page isolation doesn't actually touch the pages, it simply isolates
>> pageblocks and moves all free pages to the MIGRATE_ISOLATE freelist.
>>
>> We already place pages to the tail of the freelists when undoing
>> isolation via __putback_isolated_page(), let's do it in any case
>> (e.g., if order <= pageblock_order) and document the behavior.
>>
>> Add a "to_tail" parameter to move_freepages_block() but introduce a
>> a new move_to_free_list_tail() - similar to add_to_free_list_tail().
s/a a/a/
>>
>> This change results in all pages getting onlined via online_pages() to
>> be placed to the tail of the freelist.
>>
>> Reviewed-by: Oscar Salvador <[email protected]>
>> Cc: Andrew Morton <[email protected]>
>> Cc: Alexander Duyck <[email protected]>
>> Cc: Mel Gorman <[email protected]>
>> Cc: Michal Hocko <[email protected]>
>> Cc: Dave Hansen <[email protected]>
>> Cc: Vlastimil Babka <[email protected]>
>> Cc: Wei Yang <[email protected]>
>> Cc: Oscar Salvador <[email protected]>
>> Cc: Mike Rapoport <[email protected]>
>> Cc: Scott Cheloha <[email protected]>
>> Cc: Michael Ellerman <[email protected]>
>> Signed-off-by: David Hildenbrand <[email protected]>
>> ---
>> include/linux/page-isolation.h | 4 ++--
>> mm/page_alloc.c | 35 +++++++++++++++++++++++-----------
>> mm/page_isolation.c | 12 +++++++++---
>> 3 files changed, 35 insertions(+), 16 deletions(-)
>>
>> diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h
>> index 572458016331..3eca9b3c5305 100644
>> --- a/include/linux/page-isolation.h
>> +++ b/include/linux/page-isolation.h
>> @@ -36,8 +36,8 @@ static inline bool is_migrate_isolate(int migratetype)
>> struct page *has_unmovable_pages(struct zone *zone, struct page *page,
>> int migratetype, int flags);
>> void set_pageblock_migratetype(struct page *page, int migratetype);
>> -int move_freepages_block(struct zone *zone, struct page *page,
>> - int migratetype, int *num_movable);
>> +int move_freepages_block(struct zone *zone, struct page *page, int migratetype,
>> + bool to_tail, int *num_movable);
>>
>> /*
>> * Changes migrate type in [start_pfn, end_pfn) to be MIGRATE_ISOLATE.
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 9e3ed4a6f69a..d5a5f528b8ca 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -905,6 +905,15 @@ static inline void move_to_free_list(struct page *page, struct zone *zone,
>> list_move(&page->lru, &area->free_list[migratetype]);
>> }
>>
>> +/* Used for pages which are on another list */
>> +static inline void move_to_free_list_tail(struct page *page, struct zone *zone,
>> + unsigned int order, int migratetype)
>> +{
>> + struct free_area *area = &zone->free_area[order];
>> +
>> + list_move_tail(&page->lru, &area->free_list[migratetype]);
>> +}
>> +
>
> Would it be better to pass the *to_tail* to move_to_free_list(), so we won't
> have a new function?
Hi,
thanks for the review!
See discussion in RFC + cover letter:
"Add a "to_tail" parameter to move_freepages_block() but introduce a new
move_to_free_list_tail() - similar to add_to_free_list_tail()."
On 29.09.20 11:36, Wei Yang wrote:
> On Mon, Sep 28, 2020 at 08:21:09PM +0200, David Hildenbrand wrote:
>> __free_pages_core() is used when exposing fresh memory to the buddy
>> during system boot and when onlining memory in generic_online_page().
>>
>> generic_online_page() is used in two cases:
>>
>> 1. Direct memory onlining in online_pages().
>> 2. Deferred memory onlining in memory-ballooning-like mechanisms (HyperV
>> balloon and virtio-mem), when parts of a section are kept
>> fake-offline to be fake-onlined later on.
>>
>> In 1, we already place pages to the tail of the freelist. Pages will be
>> freed to MIGRATE_ISOLATE lists first and moved to the tail of the freelists
>> via undo_isolate_page_range().
>>
>> In 2, we currently don't implement a proper rule. In case of virtio-mem,
>> where we currently always online MAX_ORDER - 1 pages, the pages will be
>> placed to the HEAD of the freelist - undesireable. While the hyper-v
>> balloon calls generic_online_page() with single pages, usually it will
>> call it on successive single pages in a larger block.
>>
>> The pages are fresh, so place them to the tail of the freelists and avoid
>> the PCP. In __free_pages_core(), remove the now superflouos call to
>> set_page_refcounted() and add a comment regarding page initialization and
>> the refcount.
>>
>> Note: In 2. we currently don't shuffle. If ever relevant (page shuffling
>> is usually of limited use in virtualized environments), we might want to
>> shuffle after a sequence of generic_online_page() calls in the
>> relevant callers.
>>
>> Reviewed-by: Vlastimil Babka <[email protected]>
>> Reviewed-by: Oscar Salvador <[email protected]>
>> Cc: Andrew Morton <[email protected]>
>> Cc: Alexander Duyck <[email protected]>
>> Cc: Mel Gorman <[email protected]>
>> Cc: Michal Hocko <[email protected]>
>> Cc: Dave Hansen <[email protected]>
>> Cc: Vlastimil Babka <[email protected]>
>> Cc: Wei Yang <[email protected]>
>> Cc: Oscar Salvador <[email protected]>
>> Cc: Mike Rapoport <[email protected]>
>> Cc: "K. Y. Srinivasan" <[email protected]>
>> Cc: Haiyang Zhang <[email protected]>
>> Cc: Stephen Hemminger <[email protected]>
>> Cc: Wei Liu <[email protected]>
>> Signed-off-by: David Hildenbrand <[email protected]>
>> ---
>> mm/page_alloc.c | 37 ++++++++++++++++++++++++-------------
>> 1 file changed, 24 insertions(+), 13 deletions(-)
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index d5a5f528b8ca..8a2134fe9947 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -270,7 +270,8 @@ bool pm_suspended_storage(void)
>> unsigned int pageblock_order __read_mostly;
>> #endif
>>
>> -static void __free_pages_ok(struct page *page, unsigned int order);
>> +static void __free_pages_ok(struct page *page, unsigned int order,
>> + fop_t fop_flags);
>>
>> /*
>> * results with 256, 32 in the lowmem_reserve sysctl:
>> @@ -682,7 +683,7 @@ static void bad_page(struct page *page, const char *reason)
>> void free_compound_page(struct page *page)
>> {
>> mem_cgroup_uncharge(page);
>> - __free_pages_ok(page, compound_order(page));
>> + __free_pages_ok(page, compound_order(page), FOP_NONE);
>> }
>>
>> void prep_compound_page(struct page *page, unsigned int order)
>> @@ -1419,17 +1420,15 @@ static void free_pcppages_bulk(struct zone *zone, int count,
>> spin_unlock(&zone->lock);
>> }
>>
>> -static void free_one_page(struct zone *zone,
>> - struct page *page, unsigned long pfn,
>> - unsigned int order,
>> - int migratetype)
>> +static void free_one_page(struct zone *zone, struct page *page, unsigned long pfn,
>> + unsigned int order, int migratetype, fop_t fop_flags)
>> {
>> spin_lock(&zone->lock);
>> if (unlikely(has_isolate_pageblock(zone) ||
>> is_migrate_isolate(migratetype))) {
>> migratetype = get_pfnblock_migratetype(page, pfn);
>> }
>> - __free_one_page(page, pfn, zone, order, migratetype, FOP_NONE);
>> + __free_one_page(page, pfn, zone, order, migratetype, fop_flags);
>> spin_unlock(&zone->lock);
>> }
>>
>> @@ -1507,7 +1506,8 @@ void __meminit reserve_bootmem_region(phys_addr_t start, phys_addr_t end)
>> }
>> }
>>
>> -static void __free_pages_ok(struct page *page, unsigned int order)
>> +static void __free_pages_ok(struct page *page, unsigned int order,
>> + fop_t fop_flags)
>> {
>> unsigned long flags;
>> int migratetype;
>> @@ -1519,7 +1519,8 @@ static void __free_pages_ok(struct page *page, unsigned int order)
>> migratetype = get_pfnblock_migratetype(page, pfn);
>> local_irq_save(flags);
>> __count_vm_events(PGFREE, 1 << order);
>> - free_one_page(page_zone(page), page, pfn, order, migratetype);
>> + free_one_page(page_zone(page), page, pfn, order, migratetype,
>> + fop_flags);
>> local_irq_restore(flags);
>> }
>>
>> @@ -1529,6 +1530,11 @@ void __free_pages_core(struct page *page, unsigned int order)
>> struct page *p = page;
>> unsigned int loop;
>>
>> + /*
>> + * When initializing the memmap, init_single_page() sets the refcount
>
> If my code is the latest version.
>
> s/init_single_page/__init_single_page/
Indeed - thanks!
--
Thanks,
David / dhildenb
On Tue, Sep 29, 2020 at 12:12:14PM +0200, David Hildenbrand wrote:
>On 29.09.20 11:18, Wei Yang wrote:
>> On Mon, Sep 28, 2020 at 08:21:08PM +0200, David Hildenbrand wrote:
>>> Page isolation doesn't actually touch the pages, it simply isolates
>>> pageblocks and moves all free pages to the MIGRATE_ISOLATE freelist.
>>>
>>> We already place pages to the tail of the freelists when undoing
>>> isolation via __putback_isolated_page(), let's do it in any case
>>> (e.g., if order <= pageblock_order) and document the behavior.
>>>
>>> Add a "to_tail" parameter to move_freepages_block() but introduce a
>>> a new move_to_free_list_tail() - similar to add_to_free_list_tail().
>
>s/a a/a/
>
>>>
>>> This change results in all pages getting onlined via online_pages() to
>>> be placed to the tail of the freelist.
>>>
>>> Reviewed-by: Oscar Salvador <[email protected]>
>>> Cc: Andrew Morton <[email protected]>
>>> Cc: Alexander Duyck <[email protected]>
>>> Cc: Mel Gorman <[email protected]>
>>> Cc: Michal Hocko <[email protected]>
>>> Cc: Dave Hansen <[email protected]>
>>> Cc: Vlastimil Babka <[email protected]>
>>> Cc: Wei Yang <[email protected]>
>>> Cc: Oscar Salvador <[email protected]>
>>> Cc: Mike Rapoport <[email protected]>
>>> Cc: Scott Cheloha <[email protected]>
>>> Cc: Michael Ellerman <[email protected]>
>>> Signed-off-by: David Hildenbrand <[email protected]>
>>> ---
>>> include/linux/page-isolation.h | 4 ++--
>>> mm/page_alloc.c | 35 +++++++++++++++++++++++-----------
>>> mm/page_isolation.c | 12 +++++++++---
>>> 3 files changed, 35 insertions(+), 16 deletions(-)
>>>
>>> diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h
>>> index 572458016331..3eca9b3c5305 100644
>>> --- a/include/linux/page-isolation.h
>>> +++ b/include/linux/page-isolation.h
>>> @@ -36,8 +36,8 @@ static inline bool is_migrate_isolate(int migratetype)
>>> struct page *has_unmovable_pages(struct zone *zone, struct page *page,
>>> int migratetype, int flags);
>>> void set_pageblock_migratetype(struct page *page, int migratetype);
>>> -int move_freepages_block(struct zone *zone, struct page *page,
>>> - int migratetype, int *num_movable);
>>> +int move_freepages_block(struct zone *zone, struct page *page, int migratetype,
>>> + bool to_tail, int *num_movable);
>>>
>>> /*
>>> * Changes migrate type in [start_pfn, end_pfn) to be MIGRATE_ISOLATE.
>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>>> index 9e3ed4a6f69a..d5a5f528b8ca 100644
>>> --- a/mm/page_alloc.c
>>> +++ b/mm/page_alloc.c
>>> @@ -905,6 +905,15 @@ static inline void move_to_free_list(struct page *page, struct zone *zone,
>>> list_move(&page->lru, &area->free_list[migratetype]);
>>> }
>>>
>>> +/* Used for pages which are on another list */
>>> +static inline void move_to_free_list_tail(struct page *page, struct zone *zone,
>>> + unsigned int order, int migratetype)
>>> +{
>>> + struct free_area *area = &zone->free_area[order];
>>> +
>>> + list_move_tail(&page->lru, &area->free_list[migratetype]);
>>> +}
>>> +
>>
>> Would it be better to pass the *to_tail* to move_to_free_list(), so we won't
>> have a new function?
>
>Hi,
>
>thanks for the review!
>
>See discussion in RFC + cover letter:
>
>"Add a "to_tail" parameter to move_freepages_block() but introduce a new
>move_to_free_list_tail() - similar to add_to_free_list_tail()."
Hmm, sounds reasonable.
Reviewed-by: Wei Yang <[email protected]>
--
Wei Yang
Help you, Help me
On Mon 28-09-20 20:21:06, David Hildenbrand wrote:
> Let's prepare for additional flags and avoid long parameter lists of bools.
> Follow-up patches will also make use of the flags in __free_pages_ok(),
> however, I wasn't able to come up with a better name for the type - should
> be good enough for internal purposes.
>
> Reviewed-by: Alexander Duyck <[email protected]>
> Reviewed-by: Vlastimil Babka <[email protected]>
> Reviewed-by: Oscar Salvador <[email protected]>
> Cc: Andrew Morton <[email protected]>
> Cc: Alexander Duyck <[email protected]>
> Cc: Mel Gorman <[email protected]>
> Cc: Michal Hocko <[email protected]>
> Cc: Dave Hansen <[email protected]>
> Cc: Vlastimil Babka <[email protected]>
> Cc: Wei Yang <[email protected]>
> Cc: Oscar Salvador <[email protected]>
> Cc: Mike Rapoport <[email protected]>
> Signed-off-by: David Hildenbrand <[email protected]>
Hopefully this will not wrack the generated code. But considering we
would need another parameter there is not much choice left.
Acked-by: Michal Hocko <[email protected]>
> ---
> mm/page_alloc.c | 28 ++++++++++++++++++++--------
> 1 file changed, 20 insertions(+), 8 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index df90e3654f97..daab90e960fe 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -77,6 +77,18 @@
> #include "shuffle.h"
> #include "page_reporting.h"
>
> +/* Free One Page flags: for internal, non-pcp variants of free_pages(). */
> +typedef int __bitwise fop_t;
> +
> +/* No special request */
> +#define FOP_NONE ((__force fop_t)0)
> +
> +/*
> + * Skip free page reporting notification for the (possibly merged) page. (will
> + * *not* mark the page reported, only skip the notification).
> + */
> +#define FOP_SKIP_REPORT_NOTIFY ((__force fop_t)BIT(0))
> +
> /* prevent >1 _updater_ of zone percpu pageset ->high and ->batch fields */
> static DEFINE_MUTEX(pcp_batch_high_lock);
> #define MIN_PERCPU_PAGELIST_FRACTION (8)
> @@ -948,10 +960,9 @@ buddy_merge_likely(unsigned long pfn, unsigned long buddy_pfn,
> * -- nyc
> */
>
> -static inline void __free_one_page(struct page *page,
> - unsigned long pfn,
> - struct zone *zone, unsigned int order,
> - int migratetype, bool report)
> +static inline void __free_one_page(struct page *page, unsigned long pfn,
> + struct zone *zone, unsigned int order,
> + int migratetype, fop_t fop_flags)
> {
> struct capture_control *capc = task_capc(zone);
> unsigned long buddy_pfn;
> @@ -1038,7 +1049,7 @@ static inline void __free_one_page(struct page *page,
> add_to_free_list(page, zone, order, migratetype);
>
> /* Notify page reporting subsystem of freed page */
> - if (report)
> + if (!(fop_flags & FOP_SKIP_REPORT_NOTIFY))
> page_reporting_notify_free(order);
> }
>
> @@ -1379,7 +1390,7 @@ static void free_pcppages_bulk(struct zone *zone, int count,
> if (unlikely(isolated_pageblocks))
> mt = get_pageblock_migratetype(page);
>
> - __free_one_page(page, page_to_pfn(page), zone, 0, mt, true);
> + __free_one_page(page, page_to_pfn(page), zone, 0, mt, FOP_NONE);
> trace_mm_page_pcpu_drain(page, 0, mt);
> }
> spin_unlock(&zone->lock);
> @@ -1395,7 +1406,7 @@ static void free_one_page(struct zone *zone,
> is_migrate_isolate(migratetype))) {
> migratetype = get_pfnblock_migratetype(page, pfn);
> }
> - __free_one_page(page, pfn, zone, order, migratetype, true);
> + __free_one_page(page, pfn, zone, order, migratetype, FOP_NONE);
> spin_unlock(&zone->lock);
> }
>
> @@ -3288,7 +3299,8 @@ void __putback_isolated_page(struct page *page, unsigned int order, int mt)
> lockdep_assert_held(&zone->lock);
>
> /* Return isolated page to tail of freelist. */
> - __free_one_page(page, page_to_pfn(page), zone, order, mt, false);
> + __free_one_page(page, page_to_pfn(page), zone, order, mt,
> + FOP_SKIP_REPORT_NOTIFY);
> }
>
> /*
> --
> 2.26.2
--
Michal Hocko
SUSE Labs
On Mon 28-09-20 20:21:07, David Hildenbrand wrote:
> __putback_isolated_page() already documents that pages will be placed to
> the tail of the freelist - this is, however, not the case for
> "order >= MAX_ORDER - 2" (see buddy_merge_likely()) - which should be
> the case for all existing users.
>
> This change affects two users:
> - free page reporting
> - page isolation, when undoing the isolation (including memory onlining).
>
> This behavior is desireable for pages that haven't really been touched
> lately, so exactly the two users that don't actually read/write page
> content, but rather move untouched pages.
>
> The new behavior is especially desirable for memory onlining, where we
> allow allocation of newly onlined pages via undo_isolate_page_range()
> in online_pages(). Right now, we always place them to the head of the
> free list, resulting in undesireable behavior: Assume we add
> individual memory chunks via add_memory() and online them right away to
> the NORMAL zone. We create a dependency chain of unmovable allocations
> e.g., via the memmap. The memmap of the next chunk will be placed onto
> previous chunks - if the last block cannot get offlined+removed, all
> dependent ones cannot get offlined+removed. While this can already be
> observed with individual DIMMs, it's more of an issue for virtio-mem
> (and I suspect also ppc DLPAR).
>
> Document that this should only be used for optimizations, and no code
> should realy on this for correction (if the order of freepage lists
> ever changes).
>
> We won't care about page shuffling: memory onlining already properly
> shuffles after onlining. free page reporting doesn't care about
> physically contiguous ranges, and there are already cases where page
> isolation will simply move (physically close) free pages to (currently)
> the head of the freelists via move_freepages_block() instead of
> shuffling. If this becomes ever relevant, we should shuffle the whole
> zone when undoing isolation of larger ranges, and after
> free_contig_range().
>
> Reviewed-by: Alexander Duyck <[email protected]>
> Reviewed-by: Oscar Salvador <[email protected]>
> Cc: Andrew Morton <[email protected]>
> Cc: Alexander Duyck <[email protected]>
> Cc: Mel Gorman <[email protected]>
> Cc: Michal Hocko <[email protected]>
> Cc: Dave Hansen <[email protected]>
> Cc: Vlastimil Babka <[email protected]>
> Cc: Wei Yang <[email protected]>
> Cc: Oscar Salvador <[email protected]>
> Cc: Mike Rapoport <[email protected]>
> Cc: Scott Cheloha <[email protected]>
> Cc: Michael Ellerman <[email protected]>
> Signed-off-by: David Hildenbrand <[email protected]>
Acked-by: Michal Hocko <[email protected]>
> ---
> mm/page_alloc.c | 18 ++++++++++++++++--
> 1 file changed, 16 insertions(+), 2 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index daab90e960fe..9e3ed4a6f69a 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -89,6 +89,18 @@ typedef int __bitwise fop_t;
> */
> #define FOP_SKIP_REPORT_NOTIFY ((__force fop_t)BIT(0))
>
> +/*
> + * Place the (possibly merged) page to the tail of the freelist. Will ignore
> + * page shuffling (relevant code - e.g., memory onlining - is expected to
> + * shuffle the whole zone).
> + *
> + * Note: No code should rely onto this flag for correctness - it's purely
> + * to allow for optimizations when handing back either fresh pages
> + * (memory onlining) or untouched pages (page isolation, free page
> + * reporting).
> + */
> +#define FOP_TO_TAIL ((__force fop_t)BIT(1))
> +
> /* prevent >1 _updater_ of zone percpu pageset ->high and ->batch fields */
> static DEFINE_MUTEX(pcp_batch_high_lock);
> #define MIN_PERCPU_PAGELIST_FRACTION (8)
> @@ -1038,7 +1050,9 @@ static inline void __free_one_page(struct page *page, unsigned long pfn,
> done_merging:
> set_page_order(page, order);
>
> - if (is_shuffle_order(order))
> + if (fop_flags & FOP_TO_TAIL)
> + to_tail = true;
> + else if (is_shuffle_order(order))
> to_tail = shuffle_pick_tail();
> else
> to_tail = buddy_merge_likely(pfn, buddy_pfn, page, order);
> @@ -3300,7 +3314,7 @@ void __putback_isolated_page(struct page *page, unsigned int order, int mt)
>
> /* Return isolated page to tail of freelist. */
> __free_one_page(page, page_to_pfn(page), zone, order, mt,
> - FOP_SKIP_REPORT_NOTIFY);
> + FOP_SKIP_REPORT_NOTIFY | FOP_TO_TAIL);
> }
>
> /*
> --
> 2.26.2
--
Michal Hocko
SUSE Labs
On Mon 28-09-20 20:21:08, David Hildenbrand wrote:
> Page isolation doesn't actually touch the pages, it simply isolates
> pageblocks and moves all free pages to the MIGRATE_ISOLATE freelist.
>
> We already place pages to the tail of the freelists when undoing
> isolation via __putback_isolated_page(), let's do it in any case
> (e.g., if order <= pageblock_order) and document the behavior.
>
> Add a "to_tail" parameter to move_freepages_block() but introduce a
> a new move_to_free_list_tail() - similar to add_to_free_list_tail().
>
> This change results in all pages getting onlined via online_pages() to
> be placed to the tail of the freelist.
Is there anything preventing to do this unconditionally? Or in other
words is any of the existing callers of move_freepages_block benefiting
from adding to the head?
> Reviewed-by: Oscar Salvador <[email protected]>
> Cc: Andrew Morton <[email protected]>
> Cc: Alexander Duyck <[email protected]>
> Cc: Mel Gorman <[email protected]>
> Cc: Michal Hocko <[email protected]>
> Cc: Dave Hansen <[email protected]>
> Cc: Vlastimil Babka <[email protected]>
> Cc: Wei Yang <[email protected]>
> Cc: Oscar Salvador <[email protected]>
> Cc: Mike Rapoport <[email protected]>
> Cc: Scott Cheloha <[email protected]>
> Cc: Michael Ellerman <[email protected]>
> Signed-off-by: David Hildenbrand <[email protected]>
> ---
> include/linux/page-isolation.h | 4 ++--
> mm/page_alloc.c | 35 +++++++++++++++++++++++-----------
> mm/page_isolation.c | 12 +++++++++---
> 3 files changed, 35 insertions(+), 16 deletions(-)
>
> diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h
> index 572458016331..3eca9b3c5305 100644
> --- a/include/linux/page-isolation.h
> +++ b/include/linux/page-isolation.h
> @@ -36,8 +36,8 @@ static inline bool is_migrate_isolate(int migratetype)
> struct page *has_unmovable_pages(struct zone *zone, struct page *page,
> int migratetype, int flags);
> void set_pageblock_migratetype(struct page *page, int migratetype);
> -int move_freepages_block(struct zone *zone, struct page *page,
> - int migratetype, int *num_movable);
> +int move_freepages_block(struct zone *zone, struct page *page, int migratetype,
> + bool to_tail, int *num_movable);
>
> /*
> * Changes migrate type in [start_pfn, end_pfn) to be MIGRATE_ISOLATE.
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 9e3ed4a6f69a..d5a5f528b8ca 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -905,6 +905,15 @@ static inline void move_to_free_list(struct page *page, struct zone *zone,
> list_move(&page->lru, &area->free_list[migratetype]);
> }
>
> +/* Used for pages which are on another list */
> +static inline void move_to_free_list_tail(struct page *page, struct zone *zone,
> + unsigned int order, int migratetype)
> +{
> + struct free_area *area = &zone->free_area[order];
> +
> + list_move_tail(&page->lru, &area->free_list[migratetype]);
> +}
> +
> static inline void del_page_from_free_list(struct page *page, struct zone *zone,
> unsigned int order)
> {
> @@ -2338,9 +2347,9 @@ static inline struct page *__rmqueue_cma_fallback(struct zone *zone,
> * Note that start_page and end_pages are not aligned on a pageblock
> * boundary. If alignment is required, use move_freepages_block()
> */
> -static int move_freepages(struct zone *zone,
> - struct page *start_page, struct page *end_page,
> - int migratetype, int *num_movable)
> +static int move_freepages(struct zone *zone, struct page *start_page,
> + struct page *end_page, int migratetype,
> + bool to_tail, int *num_movable)
> {
> struct page *page;
> unsigned int order;
> @@ -2371,7 +2380,10 @@ static int move_freepages(struct zone *zone,
> VM_BUG_ON_PAGE(page_zone(page) != zone, page);
>
> order = page_order(page);
> - move_to_free_list(page, zone, order, migratetype);
> + if (to_tail)
> + move_to_free_list_tail(page, zone, order, migratetype);
> + else
> + move_to_free_list(page, zone, order, migratetype);
> page += 1 << order;
> pages_moved += 1 << order;
> }
> @@ -2379,8 +2391,8 @@ static int move_freepages(struct zone *zone,
> return pages_moved;
> }
>
> -int move_freepages_block(struct zone *zone, struct page *page,
> - int migratetype, int *num_movable)
> +int move_freepages_block(struct zone *zone, struct page *page, int migratetype,
> + bool to_tail, int *num_movable)
> {
> unsigned long start_pfn, end_pfn;
> struct page *start_page, *end_page;
> @@ -2401,7 +2413,7 @@ int move_freepages_block(struct zone *zone, struct page *page,
> return 0;
>
> return move_freepages(zone, start_page, end_page, migratetype,
> - num_movable);
> + to_tail, num_movable);
> }
>
> static void change_pageblock_range(struct page *pageblock_page,
> @@ -2526,8 +2538,8 @@ static void steal_suitable_fallback(struct zone *zone, struct page *page,
> if (!whole_block)
> goto single_page;
>
> - free_pages = move_freepages_block(zone, page, start_type,
> - &movable_pages);
> + free_pages = move_freepages_block(zone, page, start_type, false,
> + &movable_pages);
> /*
> * Determine how many pages are compatible with our allocation.
> * For movable allocation, it's the number of movable pages which
> @@ -2635,7 +2647,8 @@ static void reserve_highatomic_pageblock(struct page *page, struct zone *zone,
> && !is_migrate_cma(mt)) {
> zone->nr_reserved_highatomic += pageblock_nr_pages;
> set_pageblock_migratetype(page, MIGRATE_HIGHATOMIC);
> - move_freepages_block(zone, page, MIGRATE_HIGHATOMIC, NULL);
> + move_freepages_block(zone, page, MIGRATE_HIGHATOMIC, false,
> + NULL);
> }
>
> out_unlock:
> @@ -2711,7 +2724,7 @@ static bool unreserve_highatomic_pageblock(const struct alloc_context *ac,
> */
> set_pageblock_migratetype(page, ac->migratetype);
> ret = move_freepages_block(zone, page, ac->migratetype,
> - NULL);
> + false, NULL);
> if (ret) {
> spin_unlock_irqrestore(&zone->lock, flags);
> return ret;
> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> index abfe26ad59fd..de44e1329706 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -45,7 +45,7 @@ static int set_migratetype_isolate(struct page *page, int migratetype, int isol_
> set_pageblock_migratetype(page, MIGRATE_ISOLATE);
> zone->nr_isolate_pageblock++;
> nr_pages = move_freepages_block(zone, page, MIGRATE_ISOLATE,
> - NULL);
> + false, NULL);
>
> __mod_zone_freepage_state(zone, -nr_pages, mt);
> spin_unlock_irqrestore(&zone->lock, flags);
> @@ -83,7 +83,7 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype)
> * Because freepage with more than pageblock_order on isolated
> * pageblock is restricted to merge due to freepage counting problem,
> * it is possible that there is free buddy page.
> - * move_freepages_block() doesn't care of merge so we need other
> + * move_freepages_block() don't care about merging, so we need another
> * approach in order to merge them. Isolation and free will make
> * these pages to be merged.
> */
> @@ -106,9 +106,15 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype)
> * If we isolate freepage with more than pageblock_order, there
> * should be no freepage in the range, so we could avoid costly
> * pageblock scanning for freepage moving.
> + *
> + * We didn't actually touch any of the isolated pages, so place them
> + * to the tail of the freelist. This is an optimization for memory
> + * onlining - just onlined memory won't immediately be considered for
> + * allocation.
> */
> if (!isolated_page) {
> - nr_pages = move_freepages_block(zone, page, migratetype, NULL);
> + nr_pages = move_freepages_block(zone, page, migratetype, true,
> + NULL);
> __mod_zone_freepage_state(zone, nr_pages, migratetype);
> }
> set_pageblock_migratetype(page, migratetype);
> --
> 2.26.2
--
Michal Hocko
SUSE Labs
On Mon, Sep 28, 2020 at 08:21:06PM +0200, David Hildenbrand wrote:
> Let's prepare for additional flags and avoid long parameter lists of bools.
> Follow-up patches will also make use of the flags in __free_pages_ok(),
> however, I wasn't able to come up with a better name for the type - should
> be good enough for internal purposes.
> +/* Free One Page flags: for internal, non-pcp variants of free_pages(). */
> +typedef int __bitwise fop_t;
That invites confusion with f_op. There's no reason to use _t as a suffix
here ... why not free_f?
> +/*
> + * Skip free page reporting notification for the (possibly merged) page. (will
> + * *not* mark the page reported, only skip the notification).
... Don't you mean "will not skip marking the page as reported, only
skip the notification"?
*reads code*
No, I'm still confused. What does this sentence mean?
Would it help to have a FOP_DEFAULT that has FOP_REPORT_NOTIFY set and
then a FOP_SKIP_REPORT_NOTIFY define that is 0?
> -static inline void __free_one_page(struct page *page,
> - unsigned long pfn,
> - struct zone *zone, unsigned int order,
> - int migratetype, bool report)
> +static inline void __free_one_page(struct page *page, unsigned long pfn,
> + struct zone *zone, unsigned int order,
> + int migratetype, fop_t fop_flags)
Please don't over-indent like this.
static inline void __free_one_page(struct page *page, unsigned long pfn,
struct zone *zone, unsigned int order, int migratetype,
fop_t fop_flags)
reads just as well and then if someone needs to delete the 'static'
later, they don't need to fiddle around with subsequent lines getting
the whitespace to line up again.
On Mon 28-09-20 20:21:09, David Hildenbrand wrote:
> __free_pages_core() is used when exposing fresh memory to the buddy
> during system boot and when onlining memory in generic_online_page().
>
> generic_online_page() is used in two cases:
>
> 1. Direct memory onlining in online_pages().
> 2. Deferred memory onlining in memory-ballooning-like mechanisms (HyperV
> balloon and virtio-mem), when parts of a section are kept
> fake-offline to be fake-onlined later on.
>
> In 1, we already place pages to the tail of the freelist. Pages will be
> freed to MIGRATE_ISOLATE lists first and moved to the tail of the freelists
> via undo_isolate_page_range().
>
> In 2, we currently don't implement a proper rule. In case of virtio-mem,
> where we currently always online MAX_ORDER - 1 pages, the pages will be
> placed to the HEAD of the freelist - undesireable. While the hyper-v
> balloon calls generic_online_page() with single pages, usually it will
> call it on successive single pages in a larger block.
>
> The pages are fresh, so place them to the tail of the freelists and avoid
> the PCP. In __free_pages_core(), remove the now superflouos call to
> set_page_refcounted() and add a comment regarding page initialization and
> the refcount.
>
> Note: In 2. we currently don't shuffle. If ever relevant (page shuffling
> is usually of limited use in virtualized environments), we might want to
> shuffle after a sequence of generic_online_page() calls in the
> relevant callers.
It took some time to get through all the freeing paths with subtle
differences but this looks reasonable. You are mentioning that this
influences a boot time free memory ordering as well but only very
briefly. I do not expect this to make a huge difference but who knows.
It makes some sense to add pages in the order they show up in the
physical address ordering.
> Reviewed-by: Vlastimil Babka <[email protected]>
> Reviewed-by: Oscar Salvador <[email protected]>
> Cc: Andrew Morton <[email protected]>
> Cc: Alexander Duyck <[email protected]>
> Cc: Mel Gorman <[email protected]>
> Cc: Michal Hocko <[email protected]>
> Cc: Dave Hansen <[email protected]>
> Cc: Vlastimil Babka <[email protected]>
> Cc: Wei Yang <[email protected]>
> Cc: Oscar Salvador <[email protected]>
> Cc: Mike Rapoport <[email protected]>
> Cc: "K. Y. Srinivasan" <[email protected]>
> Cc: Haiyang Zhang <[email protected]>
> Cc: Stephen Hemminger <[email protected]>
> Cc: Wei Liu <[email protected]>
> Signed-off-by: David Hildenbrand <[email protected]>
That being said I do not see any fundamental problems.
Acked-by: Michal Hocko <[email protected]>
> ---
> mm/page_alloc.c | 37 ++++++++++++++++++++++++-------------
> 1 file changed, 24 insertions(+), 13 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index d5a5f528b8ca..8a2134fe9947 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -270,7 +270,8 @@ bool pm_suspended_storage(void)
> unsigned int pageblock_order __read_mostly;
> #endif
>
> -static void __free_pages_ok(struct page *page, unsigned int order);
> +static void __free_pages_ok(struct page *page, unsigned int order,
> + fop_t fop_flags);
>
> /*
> * results with 256, 32 in the lowmem_reserve sysctl:
> @@ -682,7 +683,7 @@ static void bad_page(struct page *page, const char *reason)
> void free_compound_page(struct page *page)
> {
> mem_cgroup_uncharge(page);
> - __free_pages_ok(page, compound_order(page));
> + __free_pages_ok(page, compound_order(page), FOP_NONE);
> }
>
> void prep_compound_page(struct page *page, unsigned int order)
> @@ -1419,17 +1420,15 @@ static void free_pcppages_bulk(struct zone *zone, int count,
> spin_unlock(&zone->lock);
> }
>
> -static void free_one_page(struct zone *zone,
> - struct page *page, unsigned long pfn,
> - unsigned int order,
> - int migratetype)
> +static void free_one_page(struct zone *zone, struct page *page, unsigned long pfn,
> + unsigned int order, int migratetype, fop_t fop_flags)
> {
> spin_lock(&zone->lock);
> if (unlikely(has_isolate_pageblock(zone) ||
> is_migrate_isolate(migratetype))) {
> migratetype = get_pfnblock_migratetype(page, pfn);
> }
> - __free_one_page(page, pfn, zone, order, migratetype, FOP_NONE);
> + __free_one_page(page, pfn, zone, order, migratetype, fop_flags);
> spin_unlock(&zone->lock);
> }
>
> @@ -1507,7 +1506,8 @@ void __meminit reserve_bootmem_region(phys_addr_t start, phys_addr_t end)
> }
> }
>
> -static void __free_pages_ok(struct page *page, unsigned int order)
> +static void __free_pages_ok(struct page *page, unsigned int order,
> + fop_t fop_flags)
> {
> unsigned long flags;
> int migratetype;
> @@ -1519,7 +1519,8 @@ static void __free_pages_ok(struct page *page, unsigned int order)
> migratetype = get_pfnblock_migratetype(page, pfn);
> local_irq_save(flags);
> __count_vm_events(PGFREE, 1 << order);
> - free_one_page(page_zone(page), page, pfn, order, migratetype);
> + free_one_page(page_zone(page), page, pfn, order, migratetype,
> + fop_flags);
> local_irq_restore(flags);
> }
>
> @@ -1529,6 +1530,11 @@ void __free_pages_core(struct page *page, unsigned int order)
> struct page *p = page;
> unsigned int loop;
>
> + /*
> + * When initializing the memmap, init_single_page() sets the refcount
> + * of all pages to 1 ("allocated"/"not free"). We have to set the
> + * refcount of all involved pages to 0.
> + */
> prefetchw(p);
> for (loop = 0; loop < (nr_pages - 1); loop++, p++) {
> prefetchw(p + 1);
> @@ -1539,8 +1545,12 @@ void __free_pages_core(struct page *page, unsigned int order)
> set_page_count(p, 0);
>
> atomic_long_add(nr_pages, &page_zone(page)->managed_pages);
> - set_page_refcounted(page);
> - __free_pages(page, order);
> +
> + /*
> + * Bypass PCP and place fresh pages right to the tail, primarily
> + * relevant for memory onlining.
> + */
> + __free_pages_ok(page, order, FOP_TO_TAIL);
> }
>
> #ifdef CONFIG_NEED_MULTIPLE_NODES
> @@ -3171,7 +3181,8 @@ static void free_unref_page_commit(struct page *page, unsigned long pfn)
> */
> if (migratetype >= MIGRATE_PCPTYPES) {
> if (unlikely(is_migrate_isolate(migratetype))) {
> - free_one_page(zone, page, pfn, 0, migratetype);
> + free_one_page(zone, page, pfn, 0, migratetype,
> + FOP_NONE);
> return;
> }
> migratetype = MIGRATE_MOVABLE;
> @@ -5063,7 +5074,7 @@ static inline void free_the_page(struct page *page, unsigned int order)
> if (order == 0) /* Via pcp? */
> free_unref_page(page);
> else
> - __free_pages_ok(page, order);
> + __free_pages_ok(page, order, FOP_NONE);
> }
>
> void __free_pages(struct page *page, unsigned int order)
> --
> 2.26.2
>
--
Michal Hocko
SUSE Labs
On Mon 28-09-20 20:21:10, David Hildenbrand wrote:
> As we no longer shuffle via generic_online_page() and when undoing
> isolation, we can simplify the comment.
>
> We now effectively shuffle only once (properly) when onlining new
> memory.
>
> Cc: Andrew Morton <[email protected]>
> Cc: Alexander Duyck <[email protected]>
> Cc: Mel Gorman <[email protected]>
> Cc: Michal Hocko <[email protected]>
> Cc: Dave Hansen <[email protected]>
> Cc: Vlastimil Babka <[email protected]>
> Cc: Wei Yang <[email protected]>
> Cc: Oscar Salvador <[email protected]>
> Cc: Mike Rapoport <[email protected]>
> Signed-off-by: David Hildenbrand <[email protected]>
Acked-by: Michal Hocko <[email protected]>
> ---
> mm/memory_hotplug.c | 11 ++++-------
> 1 file changed, 4 insertions(+), 7 deletions(-)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 9db80ee29caa..c589bd8801bb 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -859,13 +859,10 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
> undo_isolate_page_range(pfn, pfn + nr_pages, MIGRATE_MOVABLE);
>
> /*
> - * When exposing larger, physically contiguous memory areas to the
> - * buddy, shuffling in the buddy (when freeing onlined pages, putting
> - * them either to the head or the tail of the freelist) is only helpful
> - * for maintaining the shuffle, but not for creating the initial
> - * shuffle. Shuffle the whole zone to make sure the just onlined pages
> - * are properly distributed across the whole freelist. Make sure to
> - * shuffle once pageblocks are no longer isolated.
> + * Freshly onlined pages aren't shuffled (e.g., all pages are placed to
> + * the tail of the freelist when undoing isolation). Shuffle the whole
> + * zone to make sure the just onlined pages are properly distributed
> + * across the whole freelist - to create an initial shuffle.
> */
> shuffle_zone(zone);
>
> --
> 2.26.2
--
Michal Hocko
SUSE Labs
On 02.10.20 15:41, Matthew Wilcox wrote:
> On Mon, Sep 28, 2020 at 08:21:06PM +0200, David Hildenbrand wrote:
>> Let's prepare for additional flags and avoid long parameter lists of bools.
>> Follow-up patches will also make use of the flags in __free_pages_ok(),
>> however, I wasn't able to come up with a better name for the type - should
>> be good enough for internal purposes.
>
>> +/* Free One Page flags: for internal, non-pcp variants of free_pages(). */
>> +typedef int __bitwise fop_t;
>
> That invites confusion with f_op. There's no reason to use _t as a suffix
> here ... why not free_f?
git grep "bitwise" | grep typedef | grep include/linux
indicates that "_t" it the right thing to do.
I want a name that highlights that is is for the internal variants of
free_page(), free_f / free_t is too generic.
fpi_t (Free Page Internal) ?
>
>> +/*
>> + * Skip free page reporting notification for the (possibly merged) page. (will
>> + * *not* mark the page reported, only skip the notification).
>
> ... Don't you mean "will not skip marking the page as reported, only
> skip the notification"?
Yeah, I can use that.
The way free page reporting works is that
1. Free page reporting infrastructure will get notified after buddy
merging about a newly freed page.
2. Once a certain threshold of free pages is reached, it will pull pages
from the freelist, report them, and mark them as reported. (see
mm/page_reporting.c)
During 2., we didn't actually free a "new page", we only temporarily
removed it from the list, that's why we have to skip the notification.
What we do here is skip 1., not 2.
>
> *reads code*
>
> No, I'm still confused. What does this sentence mean?
>
> Would it help to have a FOP_DEFAULT that has FOP_REPORT_NOTIFY set and
> then a FOP_SKIP_REPORT_NOTIFY define that is 0?
Hmm, I'm not entirely sure if that improves the situation. Then, I need
3 defines instead of two, and an "inverse" documentation for
FOP_REPORT_NOTIFY.
>
>> -static inline void __free_one_page(struct page *page,
>> - unsigned long pfn,
>> - struct zone *zone, unsigned int order,
>> - int migratetype, bool report)
>> +static inline void __free_one_page(struct page *page, unsigned long pfn,
>> + struct zone *zone, unsigned int order,
>> + int migratetype, fop_t fop_flags)
>
> Please don't over-indent like this.
>
> static inline void __free_one_page(struct page *page, unsigned long pfn,
> struct zone *zone, unsigned int order, int migratetype,
> fop_t fop_flags)
>
> reads just as well and then if someone needs to delete the 'static'
> later, they don't need to fiddle around with subsequent lines getting
> the whitespace to line up again.
>
I don't care too much about this specific instance and can fix it up.
(this is clearly a matter of personal taste)
Thanks!
--
Thanks,
David / dhildenb
On 02.10.20 16:48, David Hildenbrand wrote:
> On 02.10.20 15:41, Matthew Wilcox wrote:
>> On Mon, Sep 28, 2020 at 08:21:06PM +0200, David Hildenbrand wrote:
>>> Let's prepare for additional flags and avoid long parameter lists of bools.
>>> Follow-up patches will also make use of the flags in __free_pages_ok(),
>>> however, I wasn't able to come up with a better name for the type - should
>>> be good enough for internal purposes.
>>
>>> +/* Free One Page flags: for internal, non-pcp variants of free_pages(). */
>>> +typedef int __bitwise fop_t;
>>
>> That invites confusion with f_op. There's no reason to use _t as a suffix
>> here ... why not free_f?
>
> git grep "bitwise" | grep typedef | grep include/linux
>
> indicates that "_t" it the right thing to do.
>
> I want a name that highlights that is is for the internal variants of
> free_page(), free_f / free_t is too generic.
>
> fpi_t (Free Page Internal) ?
>
>>
>>> +/*
>>> + * Skip free page reporting notification for the (possibly merged) page. (will
>>> + * *not* mark the page reported, only skip the notification).
>>
>> ... Don't you mean "will not skip marking the page as reported, only
>> skip the notification"?
>
> Yeah, I can use that.
Reading again, it doesn't quite fit. Marking pages as reported is
handled by mm/page_reporting.c
/*
* Skip free page reporting notification for the (possibly merged) page.
* This does not hinder free page reporting from grabbing the page,
* reporting it and marking it "reported" - it only skips notifying
* the free page reporting infrastructure about a newly freed page. For
* example, used when temporarily pulling a page from the freelist and
* putting it back unmodified.
*/
Is that clearer?
--
Thanks,
David / dhildenb
On 02.10.20 15:41, Michal Hocko wrote:
> On Mon 28-09-20 20:21:09, David Hildenbrand wrote:
>> __free_pages_core() is used when exposing fresh memory to the buddy
>> during system boot and when onlining memory in generic_online_page().
>>
>> generic_online_page() is used in two cases:
>>
>> 1. Direct memory onlining in online_pages().
>> 2. Deferred memory onlining in memory-ballooning-like mechanisms (HyperV
>> balloon and virtio-mem), when parts of a section are kept
>> fake-offline to be fake-onlined later on.
>>
>> In 1, we already place pages to the tail of the freelist. Pages will be
>> freed to MIGRATE_ISOLATE lists first and moved to the tail of the freelists
>> via undo_isolate_page_range().
>>
>> In 2, we currently don't implement a proper rule. In case of virtio-mem,
>> where we currently always online MAX_ORDER - 1 pages, the pages will be
>> placed to the HEAD of the freelist - undesireable. While the hyper-v
>> balloon calls generic_online_page() with single pages, usually it will
>> call it on successive single pages in a larger block.
>>
>> The pages are fresh, so place them to the tail of the freelists and avoid
>> the PCP. In __free_pages_core(), remove the now superflouos call to
>> set_page_refcounted() and add a comment regarding page initialization and
>> the refcount.
>>
>> Note: In 2. we currently don't shuffle. If ever relevant (page shuffling
>> is usually of limited use in virtualized environments), we might want to
>> shuffle after a sequence of generic_online_page() calls in the
>> relevant callers.
>
> It took some time to get through all the freeing paths with subtle
> differences but this looks reasonable. You are mentioning that this
> influences a boot time free memory ordering as well but only very
> briefly. I do not expect this to make a huge difference but who knows.
> It makes some sense to add pages in the order they show up in the
> physical address ordering.
I think boot memory is mostly exposed in the physical address ordering.
In that case, higher addresses will now be used less likely immediately
after this patch. I also don't think it's an issue - if we still detect
it's an issue it's fairly easy to change again.
Thanks!
--
Thanks,
David / dhildenb
On 02.10.20 15:24, Michal Hocko wrote:
> On Mon 28-09-20 20:21:08, David Hildenbrand wrote:
>> Page isolation doesn't actually touch the pages, it simply isolates
>> pageblocks and moves all free pages to the MIGRATE_ISOLATE freelist.
>>
>> We already place pages to the tail of the freelists when undoing
>> isolation via __putback_isolated_page(), let's do it in any case
>> (e.g., if order <= pageblock_order) and document the behavior.
>>
>> Add a "to_tail" parameter to move_freepages_block() but introduce a
>> a new move_to_free_list_tail() - similar to add_to_free_list_tail().
>>
>> This change results in all pages getting onlined via online_pages() to
>> be placed to the tail of the freelist.
>
> Is there anything preventing to do this unconditionally? Or in other
> words is any of the existing callers of move_freepages_block benefiting
> from adding to the head?
1. mm/page_isolation.c:set_migratetype_isolate()
We move stuff to the MIGRATE_ISOLATE list, we don't care about the order
there.
2. steal_suitable_fallback():
I don't think we care too much about the order when already stealing
pageblocks ... and the freelist is empty I guess?
3. reserve_highatomic_pageblock()/unreserve_highatomic_pageblock()
Not sure if we really care.
Good question, I tried to be careful of what I touch. Thoughts?
--
Thanks,
David / dhildenb
On Fri 02-10-20 17:20:09, David Hildenbrand wrote:
> On 02.10.20 15:24, Michal Hocko wrote:
> > On Mon 28-09-20 20:21:08, David Hildenbrand wrote:
> >> Page isolation doesn't actually touch the pages, it simply isolates
> >> pageblocks and moves all free pages to the MIGRATE_ISOLATE freelist.
> >>
> >> We already place pages to the tail of the freelists when undoing
> >> isolation via __putback_isolated_page(), let's do it in any case
> >> (e.g., if order <= pageblock_order) and document the behavior.
> >>
> >> Add a "to_tail" parameter to move_freepages_block() but introduce a
> >> a new move_to_free_list_tail() - similar to add_to_free_list_tail().
> >>
> >> This change results in all pages getting onlined via online_pages() to
> >> be placed to the tail of the freelist.
> >
> > Is there anything preventing to do this unconditionally? Or in other
> > words is any of the existing callers of move_freepages_block benefiting
> > from adding to the head?
>
> 1. mm/page_isolation.c:set_migratetype_isolate()
>
> We move stuff to the MIGRATE_ISOLATE list, we don't care about the order
> there.
>
> 2. steal_suitable_fallback():
>
> I don't think we care too much about the order when already stealing
> pageblocks ... and the freelist is empty I guess?
>
> 3. reserve_highatomic_pageblock()/unreserve_highatomic_pageblock()
>
> Not sure if we really care.
Honestly, I have no idea. I can imagine that some atomic high order
workloads (e.g. in net) might benefit from cache line hot pages but I am
not sure this is really observable. If yes it would likely be better to
have this documented than relying on wild guess. If we do not have any
evidence then I would vote for simplicity first and go with
unconditional add_to_tail which would simply your patch a bit.
Maybe Vlastimil or Mel would have a better picture.
--
Michal Hocko
SUSE Labs
On Mon, Oct 05, 2020 at 08:56:48AM +0200, Michal Hocko wrote:
> On Fri 02-10-20 17:20:09, David Hildenbrand wrote:
> > On 02.10.20 15:24, Michal Hocko wrote:
> > > On Mon 28-09-20 20:21:08, David Hildenbrand wrote:
> > >> Page isolation doesn't actually touch the pages, it simply isolates
> > >> pageblocks and moves all free pages to the MIGRATE_ISOLATE freelist.
> > >>
> > >> We already place pages to the tail of the freelists when undoing
> > >> isolation via __putback_isolated_page(), let's do it in any case
> > >> (e.g., if order <= pageblock_order) and document the behavior.
> > >>
> > >> Add a "to_tail" parameter to move_freepages_block() but introduce a
> > >> a new move_to_free_list_tail() - similar to add_to_free_list_tail().
> > >>
> > >> This change results in all pages getting onlined via online_pages() to
> > >> be placed to the tail of the freelist.
> > >
> > > Is there anything preventing to do this unconditionally? Or in other
> > > words is any of the existing callers of move_freepages_block benefiting
> > > from adding to the head?
> >
> > 1. mm/page_isolation.c:set_migratetype_isolate()
> >
> > We move stuff to the MIGRATE_ISOLATE list, we don't care about the order
> > there.
> >
> > 2. steal_suitable_fallback():
> >
> > I don't think we care too much about the order when already stealing
> > pageblocks ... and the freelist is empty I guess?
> >
> > 3. reserve_highatomic_pageblock()/unreserve_highatomic_pageblock()
> >
> > Not sure if we really care.
>
> Honestly, I have no idea. I can imagine that some atomic high order
> workloads (e.g. in net) might benefit from cache line hot pages but I am
> not sure this is really observable.
The highatomic reserve is more concerned that about the allocation
succeeding than it is about cache hotness.
--
Mel Gorman
SUSE Labs
On 05.10.20 10:20, Mel Gorman wrote:
> On Mon, Oct 05, 2020 at 08:56:48AM +0200, Michal Hocko wrote:
>> On Fri 02-10-20 17:20:09, David Hildenbrand wrote:
>>> On 02.10.20 15:24, Michal Hocko wrote:
>>>> On Mon 28-09-20 20:21:08, David Hildenbrand wrote:
>>>>> Page isolation doesn't actually touch the pages, it simply isolates
>>>>> pageblocks and moves all free pages to the MIGRATE_ISOLATE freelist.
>>>>>
>>>>> We already place pages to the tail of the freelists when undoing
>>>>> isolation via __putback_isolated_page(), let's do it in any case
>>>>> (e.g., if order <= pageblock_order) and document the behavior.
>>>>>
>>>>> Add a "to_tail" parameter to move_freepages_block() but introduce a
>>>>> a new move_to_free_list_tail() - similar to add_to_free_list_tail().
>>>>>
>>>>> This change results in all pages getting onlined via online_pages() to
>>>>> be placed to the tail of the freelist.
>>>>
>>>> Is there anything preventing to do this unconditionally? Or in other
>>>> words is any of the existing callers of move_freepages_block benefiting
>>>> from adding to the head?
>>>
>>> 1. mm/page_isolation.c:set_migratetype_isolate()
>>>
>>> We move stuff to the MIGRATE_ISOLATE list, we don't care about the order
>>> there.
>>>
>>> 2. steal_suitable_fallback():
>>>
>>> I don't think we care too much about the order when already stealing
>>> pageblocks ... and the freelist is empty I guess?
>>>
>>> 3. reserve_highatomic_pageblock()/unreserve_highatomic_pageblock()
>>>
>>> Not sure if we really care.
>>
>> Honestly, I have no idea. I can imagine that some atomic high order
>> workloads (e.g. in net) might benefit from cache line hot pages but I am
>> not sure this is really observable.
>
> The highatomic reserve is more concerned that about the allocation
> succeeding than it is about cache hotness.
>
Thanks Mel and Michal. I'll simplify this patch then - and if it turns
out to be an actual problem, we can change that one instance, adding a
proper comment.
Thanks!
--
Thanks,
David / dhildenb