Physical memory hotadd has to allocate a memmap (struct page array) for
the newly added memory section. Currently, alloc_pages_node() is used
for those allocations.
This has some disadvantages:
a) an existing memory is consumed for that purpose
(eg: ~2MB per 128MB memory section on x86_64)
b) if the whole node is movable then we have off-node struct pages
which has performance drawbacks.
c) It might be there are no PMD_ALIGNED chunks so memmap array gets
populated with base pages.
This can be improved when CONFIG_SPARSEMEM_VMEMMAP is enabled.
Vmemap page tables can map arbitrary memory.
That means that we can simply use the beginning of each memory section and
map struct pages there.
struct pages which back the allocated space then just need to be treated
carefully.
Implementation wise we will reuse vmem_altmap infrastructure to override
the default allocator used by __populate_section_memmap.
Part of the implementation also relies on memory_block structure gaining
a new field which specifies the number of vmemmap_pages at the beginning.
This comes in handy as in {online,offline}_pages, all the isolation and
migration is being done on (buddy_start_pfn, end_pfn] range,
being buddy_start_pfn = start_pfn + nr_vmemmap_pages.
In this way, we have:
[start_pfn, buddy_start_pfn - 1] = Initialized and PageReserved
[buddy_start_pfn, end_pfn - 1] = Initialized and sent to buddy
Hot-remove:
We need to be careful when removing memory, as adding and
removing memory needs to be done with the same granularity.
To check that this assumption is not violated, we check the
memory range we want to remove and if a) any memory block has
vmemmap pages and b) the range spans more than a single memory
block, we scream out loud and refuse to proceed.
If all is good and the range was using memmap on memory (aka vmemmap pages),
we construct an altmap structure so free_hugepage_table does the right
thing and calls vmem_altmap_free instead of free_pagetable.
Signed-off-by: Oscar Salvador <[email protected]>
---
drivers/base/memory.c | 20 +++---
include/linux/memory.h | 8 ++-
include/linux/memory_hotplug.h | 21 ++++--
include/linux/memremap.h | 2 +-
include/linux/mmzone.h | 5 ++
mm/Kconfig | 4 ++
mm/memory_hotplug.c | 149 +++++++++++++++++++++++++++++++++++------
mm/page_alloc.c | 4 +-
8 files changed, 177 insertions(+), 36 deletions(-)
diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index f35298425575..5ea2b3fbce02 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -175,7 +175,7 @@ int memory_notify(unsigned long val, void *v)
*/
static int
memory_block_action(unsigned long start_section_nr, unsigned long action,
- int online_type, int nid)
+ int online_type, int nid, unsigned long nr_vmemmap_pages)
{
unsigned long start_pfn;
unsigned long nr_pages = PAGES_PER_SECTION * sections_per_block;
@@ -185,10 +185,11 @@ memory_block_action(unsigned long start_section_nr, unsigned long action,
switch (action) {
case MEM_ONLINE:
- ret = online_pages(start_pfn, nr_pages, online_type, nid);
+ ret = online_pages(start_pfn, nr_pages, nr_vmemmap_pages,
+ online_type, nid);
break;
case MEM_OFFLINE:
- ret = offline_pages(start_pfn, nr_pages);
+ ret = offline_pages(start_pfn, nr_pages, nr_vmemmap_pages);
break;
default:
WARN(1, KERN_WARNING "%s(%ld, %ld) unknown action: "
@@ -211,7 +212,7 @@ static int memory_block_change_state(struct memory_block *mem,
mem->state = MEM_GOING_OFFLINE;
ret = memory_block_action(mem->start_section_nr, to_state,
- mem->online_type, mem->nid);
+ mem->online_type, mem->nid, mem->nr_vmemmap_pages);
mem->state = ret ? from_state_req : to_state;
@@ -567,7 +568,8 @@ int register_memory(struct memory_block *memory)
return ret;
}
-static int init_memory_block(unsigned long block_id, unsigned long state)
+static int init_memory_block(unsigned long block_id, unsigned long state,
+ unsigned long nr_vmemmap_pages)
{
struct memory_block *mem;
int ret = 0;
@@ -584,6 +586,7 @@ static int init_memory_block(unsigned long block_id, unsigned long state)
mem->start_section_nr = block_id * sections_per_block;
mem->state = state;
mem->nid = NUMA_NO_NODE;
+ mem->nr_vmemmap_pages = nr_vmemmap_pages;
ret = register_memory(mem);
@@ -603,7 +606,7 @@ static int add_memory_block(unsigned long base_section_nr)
if (section_count == 0)
return 0;
return init_memory_block(memory_block_id(base_section_nr),
- MEM_ONLINE);
+ MEM_ONLINE, 0);
}
static void unregister_memory(struct memory_block *memory)
@@ -625,7 +628,8 @@ static void unregister_memory(struct memory_block *memory)
*
* Called under device_hotplug_lock.
*/
-int create_memory_block_devices(unsigned long start, unsigned long size)
+int create_memory_block_devices(unsigned long start, unsigned long size,
+ unsigned long vmemmap_pages)
{
const unsigned long start_block_id = pfn_to_block_id(PFN_DOWN(start));
unsigned long end_block_id = pfn_to_block_id(PFN_DOWN(start + size));
@@ -638,7 +642,7 @@ int create_memory_block_devices(unsigned long start, unsigned long size)
return -EINVAL;
for (block_id = start_block_id; block_id != end_block_id; block_id++) {
- ret = init_memory_block(block_id, MEM_OFFLINE);
+ ret = init_memory_block(block_id, MEM_OFFLINE, vmemmap_pages);
if (ret)
break;
}
diff --git a/include/linux/memory.h b/include/linux/memory.h
index 4da95e684e20..97e92e8b556a 100644
--- a/include/linux/memory.h
+++ b/include/linux/memory.h
@@ -29,6 +29,11 @@ struct memory_block {
int online_type; /* for passing data to online routine */
int nid; /* NID for this memory block */
struct device dev;
+ /*
+ * Number of vmemmap pages. These pages
+ * lay at the beginning of the memory block.
+ */
+ unsigned long nr_vmemmap_pages;
};
int arch_get_memory_phys_device(unsigned long start_pfn);
@@ -80,7 +85,8 @@ static inline int memory_notify(unsigned long val, void *v)
#else
extern int register_memory_notifier(struct notifier_block *nb);
extern void unregister_memory_notifier(struct notifier_block *nb);
-int create_memory_block_devices(unsigned long start, unsigned long size);
+int create_memory_block_devices(unsigned long start, unsigned long size,
+ unsigned long vmemmap_pages);
void remove_memory_block_devices(unsigned long start, unsigned long size);
extern void memory_dev_init(void);
extern int memory_notify(unsigned long val, void *v);
diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index 7288aa5ef73b..a85d4b7d15c2 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -55,6 +55,14 @@ typedef int __bitwise mhp_t;
*/
#define MHP_MERGE_RESOURCE ((__force mhp_t)BIT(0))
+/*
+ * We want memmap (struct page array) to be self contained.
+ * To do so, we will use the beginning of the hot-added range to build
+ * the page tables for the memmap array that describes the entire range.
+ * Only selected architectures support it with SPARSE_VMEMMAP.
+ */
+#define MHP_MEMMAP_ON_MEMORY ((__force mhp_t)BIT(1))
+
/*
* Extended parameters for memory hotplug:
* altmap: alternative allocator for memmap array (optional)
@@ -101,11 +109,13 @@ extern int zone_grow_waitqueues(struct zone *zone, unsigned long nr_pages);
extern int add_one_highpage(struct page *page, int pfn, int bad_ppro);
/* VM interface that may be used by firmware interface */
extern int online_pages(unsigned long pfn, unsigned long nr_pages,
- int online_type, int nid);
+ unsigned long nr_vmemmap_pages, int online_type,
+ int nid);
extern struct zone *test_pages_in_a_zone(unsigned long start_pfn,
unsigned long end_pfn);
extern void __offline_isolated_pages(unsigned long start_pfn,
- unsigned long end_pfn);
+ unsigned long end_pfn,
+ unsigned long buddy_start_pfn);
typedef void (*online_page_callback_t)(struct page *page, unsigned int order);
@@ -307,7 +317,8 @@ static inline void pgdat_resize_init(struct pglist_data *pgdat) {}
#ifdef CONFIG_MEMORY_HOTREMOVE
extern void try_offline_node(int nid);
-extern int offline_pages(unsigned long start_pfn, unsigned long nr_pages);
+extern int offline_pages(unsigned long start_pfn, unsigned long nr_pages,
+ unsigned long nr_vmemmap_pages);
extern int remove_memory(int nid, u64 start, u64 size);
extern void __remove_memory(int nid, u64 start, u64 size);
extern int offline_and_remove_memory(int nid, u64 start, u64 size);
@@ -315,7 +326,8 @@ extern int offline_and_remove_memory(int nid, u64 start, u64 size);
#else
static inline void try_offline_node(int nid) {}
-static inline int offline_pages(unsigned long start_pfn, unsigned long nr_pages)
+static inline int offline_pages(unsigned long start_pfn, unsigned long nr_pages,
+ unsigned long nr_vmemmap_pages)
{
return -EINVAL;
}
@@ -359,6 +371,7 @@ extern struct zone *zone_for_pfn_range(int online_type, int nid, unsigned start_
extern int arch_create_linear_mapping(int nid, u64 start, u64 size,
struct mhp_params *params);
void arch_remove_linear_mapping(u64 start, u64 size);
+extern bool mhp_supports_memmap_on_memory(unsigned long size);
#endif /* CONFIG_MEMORY_HOTPLUG */
#endif /* __LINUX_MEMORY_HOTPLUG_H */
diff --git a/include/linux/memremap.h b/include/linux/memremap.h
index f5b464daeeca..45a79da89c5f 100644
--- a/include/linux/memremap.h
+++ b/include/linux/memremap.h
@@ -17,7 +17,7 @@ struct device;
* @alloc: track pages consumed, private to vmemmap_populate()
*/
struct vmem_altmap {
- const unsigned long base_pfn;
+ unsigned long base_pfn;
const unsigned long end_pfn;
const unsigned long reserve;
unsigned long free;
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 47946cec7584..747e1c21d8e2 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -427,6 +427,11 @@ enum zone_type {
* techniques might use alloc_contig_range() to hide previously
* exposed pages from the buddy again (e.g., to implement some sort
* of memory unplug in virtio-mem).
+ * 6. Memory-hotplug: when using memmap_on_memory and onlining the memory
+ * to the MOVABLE zone, the vmemmap pages are also placed in such
+ * zone. Such pages cannot be really moved around as they are
+ * self-stored in the range, but they are treated as movable when
+ * the range they describe is about to be offlined.
*
* In general, no unmovable allocations that degrade memory offlining
* should end up in ZONE_MOVABLE. Allocators (like alloc_contig_range())
diff --git a/mm/Kconfig b/mm/Kconfig
index 24c045b24b95..de3a7b5ed216 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -183,6 +183,10 @@ config MEMORY_HOTREMOVE
depends on MEMORY_HOTPLUG && ARCH_ENABLE_MEMORY_HOTREMOVE
depends on MIGRATION
+config MHP_MEMMAP_ON_MEMORY
+ def_bool y
+ depends on SPARSEMEM_VMEMMAP && ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE
+
# Heavily threaded applications may benefit from splitting the mm-wide
# page_table_lock, so that faults on different parts of the user address
# space can be handled with less contention: split it at this NR_CPUS.
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 5ba51a8bdaeb..63e5a0e9a6f3 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -42,6 +42,8 @@
#include "internal.h"
#include "shuffle.h"
+static bool memmap_on_memory;
+
/*
* online_page_callback contains pointer to current page onlining function.
* Initially it is generic_online_page(). If it is required it could be
@@ -638,10 +640,22 @@ void generic_online_page(struct page *page, unsigned int order)
}
EXPORT_SYMBOL_GPL(generic_online_page);
-static void online_pages_range(unsigned long start_pfn, unsigned long nr_pages)
+static void online_pages_range(unsigned long start_pfn, unsigned long nr_pages,
+ unsigned long buddy_start_pfn)
{
const unsigned long end_pfn = start_pfn + nr_pages;
- unsigned long pfn;
+ unsigned long pfn = buddy_start_pfn;
+
+ /*
+ * When using memmap_on_memory, the range might be unaligned as the
+ * first pfns are used for vmemmap pages. Align it in case we need to.
+ */
+ VM_BUG_ON(!IS_ALIGNED(pfn, pageblock_nr_pages));
+
+ while (!IS_ALIGNED(pfn, MAX_ORDER_NR_PAGES)) {
+ (*online_page_callback)(pfn_to_page(pfn), pageblock_order);
+ pfn += pageblock_nr_pages;
+ }
/*
* Online the pages in MAX_ORDER - 1 aligned chunks. The callback might
@@ -649,7 +663,7 @@ static void online_pages_range(unsigned long start_pfn, unsigned long nr_pages)
* later). We account all pages as being online and belonging to this
* zone ("present").
*/
- for (pfn = start_pfn; pfn < end_pfn; pfn += MAX_ORDER_NR_PAGES)
+ for (; pfn < end_pfn; pfn += MAX_ORDER_NR_PAGES)
(*online_page_callback)(pfn_to_page(pfn), MAX_ORDER - 1);
/* mark all involved sections as online */
@@ -830,9 +844,9 @@ struct zone * zone_for_pfn_range(int online_type, int nid, unsigned start_pfn,
}
int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
- int online_type, int nid)
+ unsigned long nr_vmemmap_pages, int online_type, int nid)
{
- unsigned long flags;
+ unsigned long flags, buddy_start_pfn, buddy_nr_pages;
struct zone *zone;
int need_zonelists_rebuild = 0;
int ret;
@@ -843,11 +857,18 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
!IS_ALIGNED(pfn | nr_pages, PAGES_PER_SECTION)))
return -EINVAL;
+ buddy_start_pfn = pfn + nr_vmemmap_pages;
+ buddy_nr_pages = nr_pages - nr_vmemmap_pages;
+
mem_hotplug_begin();
/* associate pfn range with the zone */
zone = zone_for_pfn_range(online_type, nid, pfn, nr_pages);
- move_pfn_range_to_zone(zone, pfn, nr_pages, NULL, MIGRATE_ISOLATE);
+ if (nr_vmemmap_pages)
+ move_pfn_range_to_zone(zone, pfn, nr_vmemmap_pages, NULL,
+ MIGRATE_UNMOVABLE);
+ move_pfn_range_to_zone(zone, buddy_start_pfn, buddy_nr_pages, NULL,
+ MIGRATE_ISOLATE);
arg.start_pfn = pfn;
arg.nr_pages = nr_pages;
@@ -863,7 +884,7 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
* onlining, such that undo_isolate_page_range() works correctly.
*/
spin_lock_irqsave(&zone->lock, flags);
- zone->nr_isolate_pageblock += nr_pages / pageblock_nr_pages;
+ zone->nr_isolate_pageblock += buddy_nr_pages / pageblock_nr_pages;
spin_unlock_irqrestore(&zone->lock, flags);
/*
@@ -876,7 +897,7 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
setup_zone_pageset(zone);
}
- online_pages_range(pfn, nr_pages);
+ online_pages_range(pfn, nr_pages, buddy_start_pfn);
zone->present_pages += nr_pages;
pgdat_resize_lock(zone->zone_pgdat, &flags);
@@ -889,7 +910,9 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
zone_pcp_update(zone);
/* Basic onlining is complete, allow allocation of onlined pages. */
- undo_isolate_page_range(pfn, pfn + nr_pages, MIGRATE_MOVABLE);
+ undo_isolate_page_range(buddy_start_pfn,
+ buddy_start_pfn + buddy_nr_pages,
+ MIGRATE_MOVABLE);
/*
* Freshly onlined pages aren't shuffled (e.g., all pages are placed to
@@ -1064,6 +1087,36 @@ static int online_memory_block(struct memory_block *mem, void *arg)
return device_online(&mem->dev);
}
+bool mhp_supports_memmap_on_memory(unsigned long size)
+{
+ unsigned long pageblock_size = PFN_PHYS(pageblock_nr_pages);
+ unsigned long remaining_mem = size - PMD_SIZE;
+
+ /*
+ * Besides having CONFIG_MHP_MEMMAP_ON_MEMORY, we need a few more
+ * assumptions to hold true:
+ * - we are working on a single memory block granularity
+ * - the size of struct page is multiple of PMD.
+ * - the remaining memory after having used part of the range
+ * for vmemmap pages is pageblock aligned.
+ *
+ * The reason for the struct page to be multiple of PMD is because
+ * otherwise two sections would intersect a PMD. This would go against
+ * memmap-on-memory premise, as memory would stay pinned until both
+ * sections were removed.
+ *
+ * And the reason for the remaining memory to be pageblock aligned is
+ * because mm core functions work on pageblock granularity in order to
+ * change page's migratetype.
+ */
+ return memmap_on_memory &&
+ size == memory_block_size_bytes() &&
+ IS_ENABLED(CONFIG_MHP_MEMMAP_ON_MEMORY) &&
+ !(PMD_SIZE % sizeof(struct page)) &&
+ remaining_mem &&
+ IS_ALIGNED(remaining_mem, pageblock_size);
+}
+
/*
* NOTE: The caller must call lock_device_hotplug() to serialize hotplug
* and online/offline operations (triggered e.g. by sysfs).
@@ -1073,6 +1126,7 @@ static int online_memory_block(struct memory_block *mem, void *arg)
int __ref add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
{
struct mhp_params params = { .pgprot = PAGE_KERNEL };
+ struct vmem_altmap mhp_altmap = {};
u64 start, size;
bool new_node = false;
int ret;
@@ -1099,13 +1153,26 @@ int __ref add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
goto error;
new_node = ret;
+ /*
+ * Self hosted memmap array
+ */
+ if (mhp_flags & MHP_MEMMAP_ON_MEMORY) {
+ if (!mhp_supports_memmap_on_memory(size)) {
+ ret = -EINVAL;
+ goto error;
+ }
+ mhp_altmap.free = PHYS_PFN(size);
+ mhp_altmap.base_pfn = PHYS_PFN(start);
+ params.altmap = &mhp_altmap;
+ }
+
/* call arch's memory hotadd */
ret = arch_add_memory(nid, start, size, ¶ms);
if (ret < 0)
goto error;
/* create memory block devices after memory was added */
- ret = create_memory_block_devices(start, size);
+ ret = create_memory_block_devices(start, size, mhp_altmap.alloc);
if (ret) {
arch_remove_memory(nid, start, size, NULL);
goto error;
@@ -1563,10 +1630,11 @@ static int count_system_ram_pages_cb(unsigned long start_pfn,
return 0;
}
-int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages)
+int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages,
+ unsigned long nr_vmemmap_pages)
{
const unsigned long end_pfn = start_pfn + nr_pages;
- unsigned long pfn, system_ram_pages = 0;
+ unsigned long pfn, buddy_start_pfn, buddy_nr_pages, system_ram_pages = 0;
unsigned long flags;
struct zone *zone;
struct memory_notify arg;
@@ -1578,6 +1646,9 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages)
!IS_ALIGNED(start_pfn | nr_pages, PAGES_PER_SECTION)))
return -EINVAL;
+ buddy_start_pfn = start_pfn + nr_vmemmap_pages;
+ buddy_nr_pages = nr_pages - nr_vmemmap_pages;
+
mem_hotplug_begin();
/*
@@ -1613,7 +1684,7 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages)
zone_pcp_disable(zone);
/* set above range as isolated */
- ret = start_isolate_page_range(start_pfn, end_pfn,
+ ret = start_isolate_page_range(buddy_start_pfn, end_pfn,
MIGRATE_MOVABLE,
MEMORY_OFFLINE | REPORT_FAILURE);
if (ret) {
@@ -1633,7 +1704,7 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages)
}
do {
- pfn = start_pfn;
+ pfn = buddy_start_pfn;
do {
if (signal_pending(current)) {
ret = -EINTR;
@@ -1664,18 +1735,18 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages)
* offlining actually in order to make hugetlbfs's object
* counting consistent.
*/
- ret = dissolve_free_huge_pages(start_pfn, end_pfn);
+ ret = dissolve_free_huge_pages(buddy_start_pfn, end_pfn);
if (ret) {
reason = "failure to dissolve huge pages";
goto failed_removal_isolated;
}
- ret = test_pages_isolated(start_pfn, end_pfn, MEMORY_OFFLINE);
+ ret = test_pages_isolated(buddy_start_pfn, end_pfn, MEMORY_OFFLINE);
} while (ret);
/* Mark all sections offline and remove free pages from the buddy. */
- __offline_isolated_pages(start_pfn, end_pfn);
+ __offline_isolated_pages(start_pfn, end_pfn, buddy_start_pfn);
pr_debug("Offlined Pages %ld\n", nr_pages);
/*
@@ -1684,13 +1755,13 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages)
* of isolated pageblocks, memory onlining will properly revert this.
*/
spin_lock_irqsave(&zone->lock, flags);
- zone->nr_isolate_pageblock -= nr_pages / pageblock_nr_pages;
+ zone->nr_isolate_pageblock -= buddy_nr_pages / pageblock_nr_pages;
spin_unlock_irqrestore(&zone->lock, flags);
zone_pcp_enable(zone);
/* removal success */
- adjust_managed_page_count(pfn_to_page(start_pfn), -nr_pages);
+ adjust_managed_page_count(pfn_to_page(start_pfn), -buddy_nr_pages);
zone->present_pages -= nr_pages;
pgdat_resize_lock(zone->zone_pgdat, &flags);
@@ -1719,7 +1790,7 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages)
return 0;
failed_removal_isolated:
- undo_isolate_page_range(start_pfn, end_pfn, MIGRATE_MOVABLE);
+ undo_isolate_page_range(buddy_start_pfn, end_pfn, MIGRATE_MOVABLE);
memory_notify(MEM_CANCEL_OFFLINE, &arg);
failed_removal_pcplists_disabled:
zone_pcp_enable(zone);
@@ -1750,6 +1821,14 @@ static int check_memblock_offlined_cb(struct memory_block *mem, void *arg)
return 0;
}
+static int get_nr_vmemmap_pages_cb(struct memory_block *mem, void *arg)
+{
+ /*
+ * If not set, continue with the next block.
+ */
+ return mem->nr_vmemmap_pages;
+}
+
static int check_cpu_on_node(pg_data_t *pgdat)
{
int cpu;
@@ -1824,6 +1903,9 @@ EXPORT_SYMBOL(try_offline_node);
static int __ref try_remove_memory(int nid, u64 start, u64 size)
{
int rc = 0;
+ struct vmem_altmap mhp_altmap = {};
+ struct vmem_altmap *altmap = NULL;
+ unsigned long nr_vmemmap_pages = 0;
BUG_ON(check_hotplug_memory_range(start, size));
@@ -1836,6 +1918,31 @@ static int __ref try_remove_memory(int nid, u64 start, u64 size)
if (rc)
return rc;
+ /*
+ * We only support removing memory added with MHP_MEMMAP_ON_MEMORY in
+ * the same granularity it was added - a single memory block.
+ */
+ if (memmap_on_memory) {
+ nr_vmemmap_pages = walk_memory_blocks(start, size, NULL,
+ get_nr_vmemmap_pages_cb);
+ if (nr_vmemmap_pages) {
+ if (size != memory_block_size_bytes()) {
+ pr_warn("Refuse to remove %#llx - %#llx,"
+ "wrong granularity\n",
+ start, start + size);
+ return -EINVAL;
+ }
+
+ /*
+ * Let remove_pmd_table->free_hugepage_table
+ * do the right thing if we used vmem_altmap
+ * when hot-adding the range.
+ */
+ mhp_altmap.alloc = nr_vmemmap_pages;
+ altmap = &mhp_altmap;
+ }
+ }
+
/* remove memmap entry */
firmware_map_remove(start, start + size, "System RAM");
@@ -1847,7 +1954,7 @@ static int __ref try_remove_memory(int nid, u64 start, u64 size)
mem_hotplug_begin();
- arch_remove_memory(nid, start, size, NULL);
+ arch_remove_memory(nid, start, size, altmap);
if (IS_ENABLED(CONFIG_ARCH_KEEP_MEMBLOCK)) {
memblock_free(start, size);
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 3e4b29ee2b1e..85c478e374d7 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -8830,7 +8830,8 @@ void zone_pcp_reset(struct zone *zone)
* All pages in the range must be in a single zone, must not contain holes,
* must span full sections, and must be isolated before calling this function.
*/
-void __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn)
+void __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn,
+ unsigned long buddy_start_pfn)
{
unsigned long pfn = start_pfn;
struct page *page;
@@ -8841,6 +8842,7 @@ void __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn)
offline_mem_sections(pfn, end_pfn);
zone = page_zone(pfn_to_page(pfn));
spin_lock_irqsave(&zone->lock, flags);
+ pfn = buddy_start_pfn;
while (pfn < end_pfn) {
page = pfn_to_page(pfn);
/*
--
2.16.3
On 4 Mar 2021, at 4:59, Oscar Salvador wrote:
> Physical memory hotadd has to allocate a memmap (struct page array) for
> the newly added memory section. Currently, alloc_pages_node() is used
> for those allocations.
>
> This has some disadvantages:
> a) an existing memory is consumed for that purpose
> (eg: ~2MB per 128MB memory section on x86_64)
> b) if the whole node is movable then we have off-node struct pages
> which has performance drawbacks.
> c) It might be there are no PMD_ALIGNED chunks so memmap array gets
> populated with base pages.
>
> This can be improved when CONFIG_SPARSEMEM_VMEMMAP is enabled.
>
> Vmemap page tables can map arbitrary memory.
> That means that we can simply use the beginning of each memory section and
> map struct pages there.
> struct pages which back the allocated space then just need to be treated
> carefully.
>
> Implementation wise we will reuse vmem_altmap infrastructure to override
> the default allocator used by __populate_section_memmap.
> Part of the implementation also relies on memory_block structure gaining
> a new field which specifies the number of vmemmap_pages at the beginning.
> This comes in handy as in {online,offline}_pages, all the isolation and
> migration is being done on (buddy_start_pfn, end_pfn] range,
> being buddy_start_pfn = start_pfn + nr_vmemmap_pages.
>
> In this way, we have:
>
> [start_pfn, buddy_start_pfn - 1] = Initialized and PageReserved
> [buddy_start_pfn, end_pfn - 1] = Initialized and sent to buddy
+Mike for hugetlb discussion.
Just thinking about how it might impact gigantic page allocation like hugetlb.
When MHP_MEMMAP_ON_MEMORY is on, memmap pages are placed at the beginning
of each hot added memory block, so available PFNs from two consecutive
hot added memory blocks are not all contiguous, separated by memmap pages.
If the memory block size is <= 1GB, there is no way of reserving gigantic
pages for hugetlb during runtime using alloc_contig_pages from any hot
added memory. Am I getting this right?
I see this implication is documented at the high level in patch 3. Just
wonder if we want to be more specific. Or hugetlb is rarely used along
with hot-add memory.
Thanks.
—
Best Regards,
Yan Zi
On Sun, Mar 07, 2021 at 10:16:36PM -0500, Zi Yan wrote:
> +Mike for hugetlb discussion.
>
> Just thinking about how it might impact gigantic page allocation like hugetlb.
> When MHP_MEMMAP_ON_MEMORY is on, memmap pages are placed at the beginning
> of each hot added memory block, so available PFNs from two consecutive
> hot added memory blocks are not all contiguous, separated by memmap pages.
> If the memory block size is <= 1GB, there is no way of reserving gigantic
> pages for hugetlb during runtime using alloc_contig_pages from any hot
> added memory. Am I getting this right?
Yes, that is why it is stated both in boot parameter documentation and
patch changelog that this feature does not play well in those setups
where your workload is in need of large contiguous chunks of memory,
that being gigantic hugetlb or just normal memory.
> I see this implication is documented at the high level in patch 3. Just
> wonder if we want to be more specific. Or hugetlb is rarely used along
> with hot-add memory.
I think it is quite normal to see hugetlb and hotplug operations in the
same environment.
One thing excludes the other, just need to be careful when it comes to
potential pitfalls during offline operations.
I guess we could mention hugetlb pages in the documentation, if it feels
it is necesary.
--
Oscar Salvador
SUSE L3
On 08.03.21 15:04, Oscar Salvador wrote:
> On Sun, Mar 07, 2021 at 10:16:36PM -0500, Zi Yan wrote:
>> +Mike for hugetlb discussion.
>>
>> Just thinking about how it might impact gigantic page allocation like hugetlb.
>> When MHP_MEMMAP_ON_MEMORY is on, memmap pages are placed at the beginning
>> of each hot added memory block, so available PFNs from two consecutive
>> hot added memory blocks are not all contiguous, separated by memmap pages.
>> If the memory block size is <= 1GB, there is no way of reserving gigantic
>> pages for hugetlb during runtime using alloc_contig_pages from any hot
>> added memory. Am I getting this right?
>
> Yes, that is why it is stated both in boot parameter documentation and
> patch changelog that this feature does not play well in those setups
> where your workload is in need of large contiguous chunks of memory,
> that being gigantic hugetlb or just normal memory.
>
>> I see this implication is documented at the high level in patch 3. Just
>> wonder if we want to be more specific. Or hugetlb is rarely used along
>> with hot-add memory.
>
> I think it is quite normal to see hugetlb and hotplug operations in the
> same environment.
> One thing excludes the other, just need to be careful when it comes to
> potential pitfalls during offline operations.
>
> I guess we could mention hugetlb pages in the documentation, if it feels
> it is necesary.
Runtime allocation of gigantic pages without CMA is absolutely
unreliable either way. IMHO, a tunable for the admin is good enough.
--
Thanks,
David / dhildenb