LinuxLists.cc - [PATCH 0/2 v2] fix livelock because of kswapd stop

2012-06-27 07:51:52

Subject: [PATCH 0/2 v2] fix livelock because of kswapd stop

2012-06-27 07:51:54

Subject: [PATCH 1/2 v2] mm: Factor out memory isolate functions

Now mm/page_alloc.c has some memory isolation functions but they
are used oly when we enable CONFIG_{CMA|MEMORY_HOTPLUG|MEMORY_FAILURE}.
So let's make it configurable by new CONFIG_MEMORY_ISOLATION so that it
can reduce binary size and we can check it simple by
CONFIG_MEMORY_ISOLATION,
not if defined CONFIG_{CMA|MEMORY_HOTPLUG|MEMORY_FAILURE}.

This patch is based on next-20120626

* from v1
- rebase on next-20120626

Cc: Andi Kleen <[email protected]>
Cc: Marek Szyprowski <[email protected]>
Cc: KAMEZAWA Hiroyuki <[email protected]>
Signed-off-by: Minchan Kim <[email protected]>
---

Andrew, I know this patch is conflict with current mmotm totally but
I don't know what tree I should use. I hope it's a git tree instead of
quit-based version. Anyway, If you feel it's inconvenient,
let me know it and I will resend it on tree you mention.
Thanks.

drivers/base/Kconfig | 1 +
include/linux/page-isolation.h | 8 ++---
mm/Kconfig | 5 +++
mm/Makefile | 4 +--
mm/page_alloc.c | 71 ----------------------------------------
mm/page_isolation.c | 71 ++++++++++++++++++++++++++++++++++++++++
6 files changed, 83 insertions(+), 77 deletions(-)

diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
index 9b21469..08b4c52 100644
--- a/drivers/base/Kconfig
+++ b/drivers/base/Kconfig
@@ -196,6 +196,7 @@ config CMA
bool "Contiguous Memory Allocator (EXPERIMENTAL)"
depends on HAVE_DMA_CONTIGUOUS && HAVE_MEMBLOCK && EXPERIMENTAL
select MIGRATION
+ select MEMORY_ISOLATION
help
This enables the Contiguous Memory Allocator which allows drivers
to allocate big physically-contiguous blocks of memory for use with
diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h
index 3bdcab3..0569a3e 100644
--- a/include/linux/page-isolation.h
+++ b/include/linux/page-isolation.h
@@ -10,7 +10,7 @@
* free all pages in the range. test_page_isolated() can be used for
* test it.
*/
-extern int
+int
start_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
unsigned migratetype);

@@ -18,7 +18,7 @@ start_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
* Changes MIGRATE_ISOLATE to MIGRATE_MOVABLE.
* target range is [start_pfn, end_pfn)
*/
-extern int
+int
undo_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
unsigned migratetype);

@@ -30,8 +30,8 @@ int test_pages_isolated(unsigned long start_pfn, unsigned long end_pfn);
/*
* Internal functions. Changes pageblock's migrate type.
*/
-extern int set_migratetype_isolate(struct page *page);
-extern void unset_migratetype_isolate(struct page *page, unsigned migratetype);
+int set_migratetype_isolate(struct page *page);
+void unset_migratetype_isolate(struct page *page, unsigned migratetype);

#endif
diff --git a/mm/Kconfig b/mm/Kconfig
index 82fed4e..d5c8019 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -140,9 +140,13 @@ config ARCH_DISCARD_MEMBLOCK
config NO_BOOTMEM
boolean

+config MEMORY_ISOLATION
+ boolean
+
# eventually, we can have this option just 'select SPARSEMEM'
config MEMORY_HOTPLUG
bool "Allow for memory hot-add"
+ select MEMORY_ISOLATION
depends on SPARSEMEM || X86_64_ACPI_NUMA
depends on HOTPLUG && ARCH_ENABLE_MEMORY_HOTPLUG
depends on (IA64 || X86 || PPC_BOOK3S_64 || SUPERH || S390)
@@ -272,6 +276,7 @@ config MEMORY_FAILURE
depends on MMU
depends on ARCH_SUPPORTS_MEMORY_FAILURE
bool "Enable recovery from hardware memory errors"
+ select MEMORY_ISOLATION
help
Enables code to recover from some memory failures on systems
with MCA recovery. This allows a system to continue running
diff --git a/mm/Makefile b/mm/Makefile
index 25e8002..a0c7725 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -15,8 +15,7 @@ obj-y := filemap.o mempool.o oom_kill.o fadvise.o \
maccess.o page_alloc.o page-writeback.o \
readahead.o swap.o truncate.o vmscan.o shmem.o \
prio_tree.o util.o mmzone.o vmstat.o backing-dev.o \
- page_isolation.o mm_init.o mmu_context.o percpu.o \
- compaction.o $(mmu-y)
+ mm_init.o mmu_context.o percpu.o compaction.o $(mmu-y)
obj-y += init-mm.o

ifdef CONFIG_NO_BOOTMEM
@@ -55,3 +54,4 @@ obj-$(CONFIG_HWPOISON_INJECT) += hwpoison-inject.o
obj-$(CONFIG_DEBUG_KMEMLEAK) += kmemleak.o
obj-$(CONFIG_DEBUG_KMEMLEAK_TEST) += kmemleak-test.o
obj-$(CONFIG_CLEANCACHE) += cleancache.o
+obj-$(CONFIG_MEMORY_ISOLATION) += page_isolation.o
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 2c29b1c..c175fa9 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -51,7 +51,6 @@
#include <linux/page_cgroup.h>
#include <linux/debugobjects.h>
#include <linux/kmemleak.h>
-#include <linux/memory.h>
#include <linux/compaction.h>
#include <trace/events/kmem.h>
#include <linux/ftrace_event.h>
@@ -5555,76 +5554,6 @@ bool is_pageblock_removable_nolock(struct page *page)
return __count_immobile_pages(zone, page, 0);
}

-int set_migratetype_isolate(struct page *page)
-{
- struct zone *zone;
- unsigned long flags, pfn;
- struct memory_isolate_notify arg;
- int notifier_ret;
- int ret = -EBUSY;
-
- zone = page_zone(page);
-
- spin_lock_irqsave(&zone->lock, flags);
-
- pfn = page_to_pfn(page);
- arg.start_pfn = pfn;
- arg.nr_pages = pageblock_nr_pages;
- arg.pages_found = 0;
-
- /*
- * It may be possible to isolate a pageblock even if the
- * migratetype is not MIGRATE_MOVABLE. The memory isolation
- * notifier chain is used by balloon drivers to return the
- * number of pages in a range that are held by the balloon
- * driver to shrink memory. If all the pages are accounted for
- * by balloons, are free, or on the LRU, isolation can continue.
- * Later, for example, when memory hotplug notifier runs, these
- * pages reported as "can be isolated" should be isolated(freed)
- * by the balloon driver through the memory notifier chain.
- */
- notifier_ret = memory_isolate_notify(MEM_ISOLATE_COUNT, &arg);
- notifier_ret = notifier_to_errno(notifier_ret);
- if (notifier_ret)
- goto out;
- /*
- * FIXME: Now, memory hotplug doesn't call shrink_slab() by itself.
- * We just check MOVABLE pages.
- */
- if (__count_immobile_pages(zone, page, arg.pages_found))
- ret = 0;
-
- /*
- * immobile means "not-on-lru" paes. If immobile is larger than
- * removable-by-driver pages reported by notifier, we'll fail.
- */
-
-out:
- if (!ret) {
- set_pageblock_migratetype(page, MIGRATE_ISOLATE);
- move_freepages_block(zone, page, MIGRATE_ISOLATE);
- }
-
- spin_unlock_irqrestore(&zone->lock, flags);
- if (!ret)
- drain_all_pages();
- return ret;
-}
-
-void unset_migratetype_isolate(struct page *page, unsigned migratetype)
-{
- struct zone *zone;
- unsigned long flags;
- zone = page_zone(page);
- spin_lock_irqsave(&zone->lock, flags);
- if (get_pageblock_migratetype(page) != MIGRATE_ISOLATE)
- goto out;
- set_pageblock_migratetype(page, migratetype);
- move_freepages_block(zone, page, migratetype);
-out:
- spin_unlock_irqrestore(&zone->lock, flags);
-}
-
#ifdef CONFIG_CMA

static unsigned long pfn_max_align_down(unsigned long pfn)
diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index c9f0477..1a9cb36 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -5,8 +5,79 @@
#include <linux/mm.h>
#include <linux/page-isolation.h>
#include <linux/pageblock-flags.h>
+#include <linux/memory.h>
#include "internal.h"

+int set_migratetype_isolate(struct page *page)
+{
+ struct zone *zone;
+ unsigned long flags, pfn;
+ struct memory_isolate_notify arg;
+ int notifier_ret;
+ int ret = -EBUSY;
+
+ zone = page_zone(page);
+
+ spin_lock_irqsave(&zone->lock, flags);
+
+ pfn = page_to_pfn(page);
+ arg.start_pfn = pfn;
+ arg.nr_pages = pageblock_nr_pages;
+ arg.pages_found = 0;
+
+ /*
+ * It may be possible to isolate a pageblock even if the
+ * migratetype is not MIGRATE_MOVABLE. The memory isolation
+ * notifier chain is used by balloon drivers to return the
+ * number of pages in a range that are held by the balloon
+ * driver to shrink memory. If all the pages are accounted for
+ * by balloons, are free, or on the LRU, isolation can continue.
+ * Later, for example, when memory hotplug notifier runs, these
+ * pages reported as "can be isolated" should be isolated(freed)
+ * by the balloon driver through the memory notifier chain.
+ */
+ notifier_ret = memory_isolate_notify(MEM_ISOLATE_COUNT, &arg);
+ notifier_ret = notifier_to_errno(notifier_ret);
+ if (notifier_ret)
+ goto out;
+ /*
+ * FIXME: Now, memory hotplug doesn't call shrink_slab() by itself.
+ * We just check MOVABLE pages.
+ */
+ if (__count_immobile_pages(zone, page, arg.pages_found))
+ ret = 0;
+
+ /*
+ * immobile means "not-on-lru" paes. If immobile is larger than
+ * removable-by-driver pages reported by notifier, we'll fail.
+ */
+
+out:
+ if (!ret) {
+ set_pageblock_migratetype(page, MIGRATE_ISOLATE);
+ move_freepages_block(zone, page, MIGRATE_ISOLATE);
+ }
+
+ spin_unlock_irqrestore(&zone->lock, flags);
+ if (!ret)
+ drain_all_pages();
+ return ret;
+}
+
+void unset_migratetype_isolate(struct page *page, unsigned migratetype)
+{
+ struct zone *zone;
+ unsigned long flags;
+ zone = page_zone(page);
+ spin_lock_irqsave(&zone->lock, flags);
+ if (get_pageblock_migratetype(page) != MIGRATE_ISOLATE)
+ goto out;
+ set_pageblock_migratetype(page, migratetype);
+ move_freepages_block(zone, page, migratetype);
+out:
+ spin_unlock_irqrestore(&zone->lock, flags);
+}
+
static inline struct page *
__first_valid_page(unsigned long pfn, unsigned long nr_pages)
{
--
1.7.9.5

2012-06-27 07:51:56

by Minchan Kim

[permalink] [raw]

Subject: [PATCH 2/2 v2] memory-hotplug: fix kswapd looping forever problem

When hotplug offlining happens on zone A, it starts to mark freed page
as MIGRATE_ISOLATE type in buddy for preventing further allocation.
(MIGRATE_ISOLATE is very irony type because it's apparently on buddy
but we can't allocate them).
When the memory shortage happens during hotplug offlining,
current task starts to reclaim, then wake up kswapd.
Kswapd checks watermark, then go sleep because current zone_watermark_ok_safe
doesn't consider MIGRATE_ISOLATE freed page count.
Current task continue to reclaim in direct reclaim path without kswapd's helping.
The problem is that zone->all_unreclaimable is set by only kswapd
so that current task would be looping forever like below.

__alloc_pages_slowpath
restart:
wake_all_kswapd
rebalance:
__alloc_pages_direct_reclaim
do_try_to_free_pages
if global_reclaim && !all_unreclaimable
return 1; /* It means we did did_some_progress */
skip __alloc_pages_may_oom
should_alloc_retry
goto rebalance;

If we apply KOSAKI's patch[1] which doesn't depends on kswapd
about setting zone->all_unreclaimable, we can solve this problem
by killing some task in direct reclaim path. But it doesn't wake up kswapd, still.
It could be a problem still if other subsystem needs GFP_ATOMIC request.
So kswapd should consider MIGRATE_ISOLATE when it calculate free pages
BEFORE going sleep.

This patch counts the number of MIGRATE_ISOLATE page block and
zone_watermark_ok_safe will consider it if the system has such blocks
(fortunately, it's very rare so no problem in POV overhead and kswapd is never
hotpath).

Copy/modify from Mel's quote
"
Ideal solution would be "allocating" the pageblock.
It would keep the free space accounting as it is but historically,
memory hotplug didn't allocate pages because it would be difficult to
detect if a pageblock was isolated or if part of some balloon.
Allocating just full pageblocks would work around this, However,
it would play very badly with CMA.
"

[1] http://lkml.org/lkml/2012/6/14/74

* from v1
- add changelog
- make functions simple
- remove atomic variable
- discard exact isolated free page accounting.
- rebased on next-20120626

Suggested-by: KOSAKI Motohiro <[email protected]>
Cc: KAMEZAWA Hiroyuki <[email protected]>
Cc: Aaditya Kumar <[email protected]>
Cc: Mel Gorman <[email protected]>
Signed-off-by: Minchan Kim <[email protected]>
---

Aaditya, coul you confirm this patch solve your problem and
make sure nr_pageblock_isolate is zero after hotplug end?

Thanks!

include/linux/mmzone.h | 8 ++++++++
mm/page_alloc.c | 31 +++++++++++++++++++++++++++++++
mm/page_isolation.c | 29 +++++++++++++++++++++++++++--
3 files changed, 66 insertions(+), 2 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index dbc876e..6ee83b8 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -474,6 +474,14 @@ struct zone {
* rarely used fields:
*/
const char *name;
+#ifdef CONFIG_MEMORY_ISOLATION
+ /*
+ * the number of MIGRATE_ISOLATE *pageblock*.
+ * We need this for free page counting. Look at zone_watermark_ok_safe.
+ * It's protected by zone->lock
+ */
+ int nr_pageblock_isolate;
+#endif
} ____cacheline_internodealigned_in_smp;

typedef enum {
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c175fa9..b12c8ec 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -218,6 +218,11 @@ EXPORT_SYMBOL(nr_online_nodes);

int page_group_by_mobility_disabled __read_mostly;

+/*
+ * NOTE:
+ * Don't use set_pageblock_migratetype(page, MIGRATE_ISOLATE) directly.
+ * Instead, use {un}set_pageblock_isolate.
+ */
void set_pageblock_migratetype(struct page *page, int migratetype)
{
if (unlikely(page_group_by_mobility_disabled))
@@ -1614,6 +1619,23 @@ static bool __zone_watermark_ok(struct zone *z, int order, unsigned long mark,
return true;
}

+#ifdef CONFIG_MEMORY_ISOLATION
+static inline unsigned long nr_zone_isolate_freepages(struct zone *zone)
+{
+ unsigned long nr_pages = 0;
+
+ if (unlikely(zone->nr_pageblock_isolate)) {
+ nr_pages = zone->nr_pageblock_isolate * pageblock_nr_pages;
+ }
+ return nr_pages;
+}
+#else
+static inline unsigned long nr_zone_isolate_freepages(struct zone *zone)
+{
+ return 0;
+}
+#endif
+
bool zone_watermark_ok(struct zone *z, int order, unsigned long mark,
int classzone_idx, int alloc_flags)
{
@@ -1629,6 +1651,14 @@ bool zone_watermark_ok_safe(struct zone *z, int order, unsigned long mark,
if (z->percpu_drift_mark && free_pages < z->percpu_drift_mark)
free_pages = zone_page_state_snapshot(z, NR_FREE_PAGES);

+ /*
+ * If the zone has MIGRATE_ISOLATE type free page,
+ * we should consider it. nr_zone_isolate_freepages is never
+ * accurate so kswapd might not sleep although she can.
+ * But it's more desirable for memory hotplug rather than
+ * forever sleep which cause livelock in direct reclaim path.
+ */
+ free_pages -= nr_zone_isolate_freepages(z);
return __zone_watermark_ok(z, order, mark, classzone_idx, alloc_flags,
free_pages);
}
@@ -4407,6 +4437,7 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat,
lruvec_init(&zone->lruvec, zone);
zap_zone_vm_stats(zone);
zone->flags = 0;
+ zone->nr_pageblock_isolate = 0;
if (!size)
continue;

diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index 1a9cb36..c721ec0 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -8,6 +8,31 @@
#include <linux/memory.h>
#include "internal.h"

+/* called by holding zone->lock */
+static void set_pageblock_isolate(struct zone *zone, struct page *page)
+{
+ BUG_ON(page_zone(page) != zone);
+
+ if (get_pageblock_migratetype(page) == MIGRATE_ISOLATE)
+ return;
+
+ set_pageblock_migratetype(page, MIGRATE_ISOLATE);
+ zone->nr_pageblock_isolate++;
+}
+
+/* called by holding zone->lock */
+static void restore_pageblock_isolate(struct zone *zone, struct page *page,
+ int migratetype)
+{
+ BUG_ON(page_zone(page) != zone);
+ if (WARN_ON(get_pageblock_migratetype(page) != MIGRATE_ISOLATE))
+ return;
+
+ BUG_ON(zone->nr_pageblock_isolate <= 0);
+ set_pageblock_migratetype(page, migratetype);
+ zone->nr_pageblock_isolate--;
+}
+
int set_migratetype_isolate(struct page *page)
{
struct zone *zone;
@@ -54,7 +79,7 @@ int set_migratetype_isolate(struct page *page)

out:
if (!ret) {
- set_pageblock_migratetype(page, MIGRATE_ISOLATE);
+ set_pageblock_isolate(zone, page);
move_freepages_block(zone, page, MIGRATE_ISOLATE);
}

@@ -72,8 +97,8 @@ void unset_migratetype_isolate(struct page *page, unsigned migratetype)
spin_lock_irqsave(&zone->lock, flags);
if (get_pageblock_migratetype(page) != MIGRATE_ISOLATE)
goto out;
- set_pageblock_migratetype(page, migratetype);
move_freepages_block(zone, page, migratetype);
+ restore_pageblock_isolate(zone, page, migratetype);
out:
spin_unlock_irqrestore(&zone->lock, flags);
}
--
1.7.9.5

2012-06-28 07:13:39

by Kamezawa Hiroyuki

[permalink] [raw]

Subject: Re: [PATCH 1/2 v2] mm: Factor out memory isolate functions

(2012/06/27 16:51), Minchan Kim wrote:
> Now mm/page_alloc.c has some memory isolation functions but they
> are used oly when we enable CONFIG_{CMA|MEMORY_HOTPLUG|MEMORY_FAILURE}.
> So let's make it configurable by new CONFIG_MEMORY_ISOLATION so that it
> can reduce binary size and we can check it simple by
> CONFIG_MEMORY_ISOLATION,
> not if defined CONFIG_{CMA|MEMORY_HOTPLUG|MEMORY_FAILURE}.
>
> This patch is based on next-20120626
>
> * from v1
> - rebase on next-20120626
>
> Cc: Andi Kleen <[email protected]>
> Cc: Marek Szyprowski <[email protected]>
> Cc: KAMEZAWA Hiroyuki <[email protected]>
> Signed-off-by: Minchan Kim <[email protected]>

Acked-by: KAMEZAWA Hiroyuki <[email protected]>

2012-06-28 07:16:13

by Kamezawa Hiroyuki

[permalink] [raw]

Subject: Re: [PATCH 2/2 v2] memory-hotplug: fix kswapd looping forever problem

(2012/06/27 16:51), Minchan Kim wrote:
> When hotplug offlining happens on zone A, it starts to mark freed page
> as MIGRATE_ISOLATE type in buddy for preventing further allocation.
> (MIGRATE_ISOLATE is very irony type because it's apparently on buddy
> but we can't allocate them).
> When the memory shortage happens during hotplug offlining,
> current task starts to reclaim, then wake up kswapd.
> Kswapd checks watermark, then go sleep because current zone_watermark_ok_safe
> doesn't consider MIGRATE_ISOLATE freed page count.
> Current task continue to reclaim in direct reclaim path without kswapd's helping.
> The problem is that zone->all_unreclaimable is set by only kswapd
> so that current task would be looping forever like below.
>
> __alloc_pages_slowpath
> restart:
> wake_all_kswapd
> rebalance:
> __alloc_pages_direct_reclaim
> do_try_to_free_pages
> if global_reclaim && !all_unreclaimable
> return 1; /* It means we did did_some_progress */
> skip __alloc_pages_may_oom
> should_alloc_retry
> goto rebalance;
>
> If we apply KOSAKI's patch[1] which doesn't depends on kswapd
> about setting zone->all_unreclaimable, we can solve this problem
> by killing some task in direct reclaim path. But it doesn't wake up kswapd, still.
> It could be a problem still if other subsystem needs GFP_ATOMIC request.
> So kswapd should consider MIGRATE_ISOLATE when it calculate free pages
> BEFORE going sleep.
>
> This patch counts the number of MIGRATE_ISOLATE page block and
> zone_watermark_ok_safe will consider it if the system has such blocks
> (fortunately, it's very rare so no problem in POV overhead and kswapd is never
> hotpath).
>
> Copy/modify from Mel's quote
> "
> Ideal solution would be "allocating" the pageblock.
> It would keep the free space accounting as it is but historically,
> memory hotplug didn't allocate pages because it would be difficult to
> detect if a pageblock was isolated or if part of some balloon.
> Allocating just full pageblocks would work around this, However,
> it would play very badly with CMA.
> "
>
> [1] http://lkml.org/lkml/2012/6/14/74
>
> * from v1
> - add changelog
> - make functions simple
> - remove atomic variable
> - discard exact isolated free page accounting.
> - rebased on next-20120626
>
> Suggested-by: KOSAKI Motohiro <[email protected]>
> Cc: KAMEZAWA Hiroyuki <[email protected]>
> Cc: Aaditya Kumar <[email protected]>
> Cc: Mel Gorman <[email protected]>
> Signed-off-by: Minchan Kim <[email protected]>
> ---
>
> Aaditya, coul you confirm this patch solve your problem and
> make sure nr_pageblock_isolate is zero after hotplug end?
>
> Thanks!
>
> include/linux/mmzone.h | 8 ++++++++
> mm/page_alloc.c | 31 +++++++++++++++++++++++++++++++
> mm/page_isolation.c | 29 +++++++++++++++++++++++++++--
> 3 files changed, 66 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index dbc876e..6ee83b8 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -474,6 +474,14 @@ struct zone {
> * rarely used fields:
> */
> const char *name;
> +#ifdef CONFIG_MEMORY_ISOLATION
> + /*
> + * the number of MIGRATE_ISOLATE *pageblock*.
> + * We need this for free page counting. Look at zone_watermark_ok_safe.
> + * It's protected by zone->lock
> + */
> + int nr_pageblock_isolate;
> +#endif
> } ____cacheline_internodealigned_in_smp;
>
> typedef enum {
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index c175fa9..b12c8ec 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -218,6 +218,11 @@ EXPORT_SYMBOL(nr_online_nodes);
>
> int page_group_by_mobility_disabled __read_mostly;
>
> +/*
> + * NOTE:
> + * Don't use set_pageblock_migratetype(page, MIGRATE_ISOLATE) directly.
> + * Instead, use {un}set_pageblock_isolate.
> + */
> void set_pageblock_migratetype(struct page *page, int migratetype)
> {
> if (unlikely(page_group_by_mobility_disabled))
> @@ -1614,6 +1619,23 @@ static bool __zone_watermark_ok(struct zone *z, int order, unsigned long mark,
> return true;
> }
>
> +#ifdef CONFIG_MEMORY_ISOLATION
> +static inline unsigned long nr_zone_isolate_freepages(struct zone *zone)
> +{
> + unsigned long nr_pages = 0;
> +
> + if (unlikely(zone->nr_pageblock_isolate)) {
> + nr_pages = zone->nr_pageblock_isolate * pageblock_nr_pages;
> + }
> + return nr_pages;
> +}
> +#else
> +static inline unsigned long nr_zone_isolate_freepages(struct zone *zone)
> +{
> + return 0;
> +}
> +#endif
> +
> bool zone_watermark_ok(struct zone *z, int order, unsigned long mark,
> int classzone_idx, int alloc_flags)
> {
> @@ -1629,6 +1651,14 @@ bool zone_watermark_ok_safe(struct zone *z, int order, unsigned long mark,
> if (z->percpu_drift_mark && free_pages < z->percpu_drift_mark)
> free_pages = zone_page_state_snapshot(z, NR_FREE_PAGES);
>
> + /*
> + * If the zone has MIGRATE_ISOLATE type free page,
> + * we should consider it. nr_zone_isolate_freepages is never
> + * accurate so kswapd might not sleep although she can.
> + * But it's more desirable for memory hotplug rather than
> + * forever sleep which cause livelock in direct reclaim path.
> + */
> + free_pages -= nr_zone_isolate_freepages(z);

Here, free_pages could be < 0 ?

Thanks,
-Kame

2012-06-28 23:34:31

by Minchan Kim

[permalink] [raw]

Subject: Re: [PATCH 2/2 v2] memory-hotplug: fix kswapd looping forever problem

Hi Kame,

On 06/28/2012 04:13 PM, Kamezawa Hiroyuki wrote:

> (2012/06/27 16:51), Minchan Kim wrote:
>> When hotplug offlining happens on zone A, it starts to mark freed page
>> as MIGRATE_ISOLATE type in buddy for preventing further allocation.
>> (MIGRATE_ISOLATE is very irony type because it's apparently on buddy
>> but we can't allocate them).
>> When the memory shortage happens during hotplug offlining,
>> current task starts to reclaim, then wake up kswapd.
>> Kswapd checks watermark, then go sleep because current zone_watermark_ok_safe
>> doesn't consider MIGRATE_ISOLATE freed page count.
>> Current task continue to reclaim in direct reclaim path without kswapd's helping.
>> The problem is that zone->all_unreclaimable is set by only kswapd
>> so that current task would be looping forever like below.
>>
>> __alloc_pages_slowpath
>> restart:
>> wake_all_kswapd
>> rebalance:
>> __alloc_pages_direct_reclaim
>> do_try_to_free_pages
>> if global_reclaim && !all_unreclaimable
>> return 1; /* It means we did did_some_progress */
>> skip __alloc_pages_may_oom
>> should_alloc_retry
>> goto rebalance;
>>
>> If we apply KOSAKI's patch[1] which doesn't depends on kswapd
>> about setting zone->all_unreclaimable, we can solve this problem
>> by killing some task in direct reclaim path. But it doesn't wake up kswapd, still.
>> It could be a problem still if other subsystem needs GFP_ATOMIC request.
>> So kswapd should consider MIGRATE_ISOLATE when it calculate free pages
>> BEFORE going sleep.
>>
>> This patch counts the number of MIGRATE_ISOLATE page block and
>> zone_watermark_ok_safe will consider it if the system has such blocks
>> (fortunately, it's very rare so no problem in POV overhead and kswapd is never
>> hotpath).
>>
>> Copy/modify from Mel's quote
>> "
>> Ideal solution would be "allocating" the pageblock.
>> It would keep the free space accounting as it is but historically,
>> memory hotplug didn't allocate pages because it would be difficult to
>> detect if a pageblock was isolated or if part of some balloon.
>> Allocating just full pageblocks would work around this, However,
>> it would play very badly with CMA.
>> "
>>
>> [1] http://lkml.org/lkml/2012/6/14/74
>>
>> * from v1
>> - add changelog
>> - make functions simple
>> - remove atomic variable
>> - discard exact isolated free page accounting.
>> - rebased on next-20120626
>>
>> Suggested-by: KOSAKI Motohiro <[email protected]>
>> Cc: KAMEZAWA Hiroyuki <[email protected]>
>> Cc: Aaditya Kumar <[email protected]>
>> Cc: Mel Gorman <[email protected]>
>> Signed-off-by: Minchan Kim <[email protected]>
>> ---
>>
>> Aaditya, coul you confirm this patch solve your problem and
>> make sure nr_pageblock_isolate is zero after hotplug end?
>>
>> Thanks!
>>
>> include/linux/mmzone.h | 8 ++++++++
>> mm/page_alloc.c | 31 +++++++++++++++++++++++++++++++
>> mm/page_isolation.c | 29 +++++++++++++++++++++++++++--
>> 3 files changed, 66 insertions(+), 2 deletions(-)
>>
>> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
>> index dbc876e..6ee83b8 100644
>> --- a/include/linux/mmzone.h
>> +++ b/include/linux/mmzone.h
>> @@ -474,6 +474,14 @@ struct zone {
>> * rarely used fields:
>> */
>> const char *name;
>> +#ifdef CONFIG_MEMORY_ISOLATION
>> + /*
>> + * the number of MIGRATE_ISOLATE *pageblock*.
>> + * We need this for free page counting. Look at zone_watermark_ok_safe.
>> + * It's protected by zone->lock
>> + */
>> + int nr_pageblock_isolate;
>> +#endif
>> } ____cacheline_internodealigned_in_smp;
>>
>> typedef enum {
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index c175fa9..b12c8ec 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -218,6 +218,11 @@ EXPORT_SYMBOL(nr_online_nodes);
>>
>> int page_group_by_mobility_disabled __read_mostly;
>>
>> +/*
>> + * NOTE:
>> + * Don't use set_pageblock_migratetype(page, MIGRATE_ISOLATE) directly.
>> + * Instead, use {un}set_pageblock_isolate.
>> + */
>> void set_pageblock_migratetype(struct page *page, int migratetype)
>> {
>> if (unlikely(page_group_by_mobility_disabled))
>> @@ -1614,6 +1619,23 @@ static bool __zone_watermark_ok(struct zone *z, int order, unsigned long mark,
>> return true;
>> }
>>
>> +#ifdef CONFIG_MEMORY_ISOLATION
>> +static inline unsigned long nr_zone_isolate_freepages(struct zone *zone)
>> +{
>> + unsigned long nr_pages = 0;
>> +
>> + if (unlikely(zone->nr_pageblock_isolate)) {
>> + nr_pages = zone->nr_pageblock_isolate * pageblock_nr_pages;
>> + }
>> + return nr_pages;
>> +}
>> +#else
>> +static inline unsigned long nr_zone_isolate_freepages(struct zone *zone)
>> +{
>> + return 0;
>> +}
>> +#endif
>> +
>> bool zone_watermark_ok(struct zone *z, int order, unsigned long mark,
>> int classzone_idx, int alloc_flags)
>> {
>> @@ -1629,6 +1651,14 @@ bool zone_watermark_ok_safe(struct zone *z, int order, unsigned long mark,
>> if (z->percpu_drift_mark && free_pages < z->percpu_drift_mark)
>> free_pages = zone_page_state_snapshot(z, NR_FREE_PAGES);
>>
>> + /*
>> + * If the zone has MIGRATE_ISOLATE type free page,
>> + * we should consider it. nr_zone_isolate_freepages is never
>> + * accurate so kswapd might not sleep although she can.
>> + * But it's more desirable for memory hotplug rather than
>> + * forever sleep which cause livelock in direct reclaim path.
>> + */
>> + free_pages -= nr_zone_isolate_freepages(z);
>
> Here, free_pages could be < 0 ?

It could but __zone_watermark_ok returns false so kswapd is going to work
without sleep. It's not bad because nr_zone_isolate_freepages already
isn't accurate
and hotplug event is temporal so kswapd should work well after end hotplug.

--
Kind regards,
Minchan Kim