Commit 5d65c8d7 authored by Barry Song's avatar Barry Song Committed by Andrew Morton
Browse files

mm: count the number of anonymous THPs per size 

Patch series "mm: count the number of anonymous THPs per size", v4.

Knowing the number of transparent anon THPs in the system is crucial
for performance analysis. It helps in understanding the ratio and
distribution of THPs versus small folios throughout the system.

Additionally, partial unmapping by userspace can lead to significant waste
of THPs over time and increase memory reclamation pressure. We need this
information for comprehensive system tuning.


This patch (of 2):

Let's track for each anonymous THP size, how many of them are currently
allocated.  We'll track the complete lifespan of an anon THP, starting
when it becomes an anon THP ("large anon folio") (->mapping gets set),
until it gets freed (->mapping gets cleared).

Introduce a new "nr_anon" counter per THP size and adjust the
corresponding counter in the following cases:
* We allocate a new THP and call folio_add_new_anon_rmap() to map
   it the first time and turn it into an anon THP.
* We split an anon THP into multiple smaller ones.
* We migrate an anon THP, when we prepare the destination.
* We free an anon THP back to the buddy.

Note that AnonPages in /proc/meminfo currently tracks the total number of
*mapped* anonymous *pages*, and therefore has slightly different
semantics.  In the future, we might also want to track "nr_anon_mapped"
for each THP size, which might be helpful when comparing it to the number
of allocated anon THPs (long-term pinning, stuck in swapcache, memory
leaks, ...).

Further note that for now, we only track anon THPs after they got their
->mapping set, for example via folio_add_new_anon_rmap().  If we would
allocate some in the swapcache, they will only show up in the statistics
for now after they have been mapped to user space the first time, where we
call folio_add_new_anon_rmap().

[akpm@linux-foundation.org: documentation fixups, per David]
  Link: https://lkml.kernel.org/r/3e8add35-e26b-443b-8a04-1078f4bc78f6@redhat.com
Link: https://lkml.kernel.org/r/20240824010441.21308-1-21cnbao@gmail.com
Link: https://lkml.kernel.org/r/20240824010441.21308-2-21cnbao@gmail.com


Signed-off-by: default avatarBarry Song <v-songbaohua@oppo.com>
Acked-by: default avatarDavid Hildenbrand <david@redhat.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Chris Li <chrisl@kernel.org>
Cc: Chuanhua Han <hanchuanhua@oppo.com>
Cc: Kairui Song <kasong@tencent.com>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: Lance Yang <ioworker0@gmail.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shuai Yuan <yuanshuai@oppo.com>
Cc: Usama Arif <usamaarif642@gmail.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 70e59a75

Documentation/admin-guide/mm/transhuge.rst

+5 −0
Original line number Diff line number Diff line
@@ -551,6 +551,11 @@ split_deferred 
        it would free up some memory. Pages on split queue are going to

        be split under memory pressure, if splitting is possible.



nr_anon

       the number of anonymous THP we have in the whole system. These THPs

       might be currently entirely mapped or have partially unmapped/unused

       subpages.



As the system ages, allocating huge pages may be expensive as the

system uses memory compaction to copy data around memory to free a

huge page for use. There are some counters in ``/proc/vmstat`` to help

include/linux/huge_mm.h

+13 −2
Original line number Diff line number Diff line
@@ -126,6 +126,7 @@ enum mthp_stat_item { 
	MTHP_STAT_SPLIT,

	MTHP_STAT_SPLIT_FAILED,

	MTHP_STAT_SPLIT_DEFERRED,

	MTHP_STAT_NR_ANON,

	__MTHP_STAT_COUNT

};
@@ -136,14 +137,24 @@ struct mthp_stat { 


DECLARE_PER_CPU(struct mthp_stat, mthp_stats);



static inline void count_mthp_stat(int order, enum mthp_stat_item item)

static inline void mod_mthp_stat(int order, enum mthp_stat_item item, int delta)

{

	if (order <= 0 || order > PMD_ORDER)

		return;



	this_cpu_inc(mthp_stats.stats[order][item]);

	this_cpu_add(mthp_stats.stats[order][item], delta);

}



static inline void count_mthp_stat(int order, enum mthp_stat_item item)

{

	mod_mthp_stat(order, item, 1);

}



#else

static inline void mod_mthp_stat(int order, enum mthp_stat_item item, int delta)

{

}



static inline void count_mthp_stat(int order, enum mthp_stat_item item)

{

}

mm/huge_memory.c

+10 −3
Original line number Diff line number Diff line
@@ -597,6 +597,7 @@ DEFINE_MTHP_STAT_ATTR(shmem_fallback_charge, MTHP_STAT_SHMEM_FALLBACK_CHARGE); 
DEFINE_MTHP_STAT_ATTR(split, MTHP_STAT_SPLIT);

DEFINE_MTHP_STAT_ATTR(split_failed, MTHP_STAT_SPLIT_FAILED);

DEFINE_MTHP_STAT_ATTR(split_deferred, MTHP_STAT_SPLIT_DEFERRED);

DEFINE_MTHP_STAT_ATTR(nr_anon, MTHP_STAT_NR_ANON);



static struct attribute *anon_stats_attrs[] = {

	&anon_fault_alloc_attr.attr,
@@ -607,6 +608,7 @@ static struct attribute *anon_stats_attrs[] = { 
	&swpout_fallback_attr.attr,

#endif

	&split_deferred_attr.attr,

	&nr_anon_attr.attr,

	NULL,

};
@@ -3314,8 +3316,9 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list, 
	struct deferred_split *ds_queue = get_deferred_split_queue(folio);

	/* reset xarray order to new order after split */

	XA_STATE_ORDER(xas, &folio->mapping->i_pages, folio->index, new_order);

	struct anon_vma *anon_vma = NULL;

	bool is_anon = folio_test_anon(folio);

	struct address_space *mapping = NULL;

	struct anon_vma *anon_vma = NULL;

	int order = folio_order(folio);

	int extra_pins, ret;

	pgoff_t end;
@@ -3327,7 +3330,7 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list, 
	if (new_order >= folio_order(folio))

		return -EINVAL;



	if (folio_test_anon(folio)) {

	if (is_anon) {

		/* order-1 is not supported for anonymous THP. */

		if (new_order == 1) {

			VM_WARN_ONCE(1, "Cannot split to order-1 folio");
@@ -3367,7 +3370,7 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list, 
	if (folio_test_writeback(folio))

		return -EBUSY;



	if (folio_test_anon(folio)) {

	if (is_anon) {

		/*

		 * The caller does not necessarily hold an mmap_lock that would

		 * prevent the anon_vma disappearing so we first we take a
@@ -3480,6 +3483,10 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list, 
			}

		}



		if (is_anon) {

			mod_mthp_stat(order, MTHP_STAT_NR_ANON, -1);

			mod_mthp_stat(new_order, MTHP_STAT_NR_ANON, 1 << (order - new_order));

		}

		__split_huge_page(page, list, end, new_order);

		ret = 0;

	} else {

mm/migrate.c

+4 −0
Original line number Diff line number Diff line
@@ -449,6 +449,8 @@ static int __folio_migrate_mapping(struct address_space *mapping, 
		/* No turning back from here */

		newfolio->index = folio->index;

		newfolio->mapping = folio->mapping;

		if (folio_test_anon(folio) && folio_test_large(folio))

			mod_mthp_stat(folio_order(folio), MTHP_STAT_NR_ANON, 1);

		if (folio_test_swapbacked(folio))

			__folio_set_swapbacked(newfolio);
@@ -473,6 +475,8 @@ static int __folio_migrate_mapping(struct address_space *mapping, 
	 */

	newfolio->index = folio->index;

	newfolio->mapping = folio->mapping;

	if (folio_test_anon(folio) && folio_test_large(folio))

		mod_mthp_stat(folio_order(folio), MTHP_STAT_NR_ANON, 1);

	folio_ref_add(newfolio, nr); /* add cache reference */

	if (folio_test_swapbacked(folio)) {

		__folio_set_swapbacked(newfolio);

mm/page_alloc.c

+4 −1
Original line number Diff line number Diff line
@@ -1084,8 +1084,11 @@ __always_inline bool free_pages_prepare(struct page *page, 
			(page + i)->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;

		}

	}

	if (PageMappingFlags(page))

	if (PageMappingFlags(page)) {

		if (PageAnon(page))

			mod_mthp_stat(order, MTHP_STAT_NR_ANON, -1);

		page->mapping = NULL;

	}

	if (is_check_pages_enabled()) {

		if (free_page_is_bad(page))

			bad++;