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mm: count the number of partially mapped anonymous THPs per size

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When a THP is added to the deferred_list due to partially mapped, its
partial pages are unused, leading to wasted memory and potentially
increasing memory reclamation pressure.

Detailing the specifics of how unmapping occurs is quite difficult and not
that useful, so we adopt a simple approach: each time a THP enters the
deferred_list, we increment the count by 1; whenever it leaves for any
reason, we decrement the count by 1.

Link: https://lkml.kernel.org/r/20240824010441.21308-3-21cnbao@gmail.com
Signed-off-by: Barry Song <v-songbaohua@oppo.com>
Acked-by: David 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: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Barry Song 2024-08-24 13:04:41 +12:00 committed by Andrew Morton
parent 5d65c8d758
commit 8175ebfd30
3 changed files with 14 additions and 0 deletions
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7
Documentation/admin-guide/mm/transhuge.rst
View File

@ -556,6 +556,13 @@ nr_anon
might be currently entirely mapped or have partially unmapped/unused
subpages.
nr_anon_partially_mapped
the number of anonymous THP which are likely partially mapped, possibly
wasting memory, and have been queued for deferred memory reclamation.
Note that in corner some cases (e.g., failed migration), we might detect
an anonymous THP as "partially mapped" and count it here, even though it
is not actually partially mapped anymore.
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

1
include/linux/huge_mm.h
View File

@ -127,6 +127,7 @@ enum mthp_stat_item {
MTHP_STAT_SPLIT_FAILED,
MTHP_STAT_SPLIT_DEFERRED,
MTHP_STAT_NR_ANON,
MTHP_STAT_NR_ANON_PARTIALLY_MAPPED,
__MTHP_STAT_COUNT
};

6
mm/huge_memory.c
View File

@ -598,6 +598,7 @@ 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);
DEFINE_MTHP_STAT_ATTR(nr_anon_partially_mapped, MTHP_STAT_NR_ANON_PARTIALLY_MAPPED);
static struct attribute *anon_stats_attrs[] = {
&anon_fault_alloc_attr.attr,
@ -609,6 +610,7 @@ static struct attribute *anon_stats_attrs[] = {
#endif
&split_deferred_attr.attr,
&nr_anon_attr.attr,
&nr_anon_partially_mapped_attr.attr,
NULL,
};
@ -3457,6 +3459,7 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
if (folio_order(folio) > 1 &&
!list_empty(&folio->_deferred_list)) {
ds_queue->split_queue_len--;
mod_mthp_stat(folio_order(folio), MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, -1);
/*
* Reinitialize page_deferred_list after removing the
* page from the split_queue, otherwise a subsequent
@ -3523,6 +3526,7 @@ void __folio_undo_large_rmappable(struct folio *folio)
spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
if (!list_empty(&folio->_deferred_list)) {
ds_queue->split_queue_len--;
mod_mthp_stat(folio_order(folio), MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, -1);
list_del_init(&folio->_deferred_list);
}
spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
@ -3564,6 +3568,7 @@ void deferred_split_folio(struct folio *folio)
if (folio_test_pmd_mappable(folio))
count_vm_event(THP_DEFERRED_SPLIT_PAGE);
count_mthp_stat(folio_order(folio), MTHP_STAT_SPLIT_DEFERRED);
mod_mthp_stat(folio_order(folio), MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, 1);
list_add_tail(&folio->_deferred_list, &ds_queue->split_queue);
ds_queue->split_queue_len++;
#ifdef CONFIG_MEMCG
@ -3611,6 +3616,7 @@ static unsigned long deferred_split_scan(struct shrinker *shrink,
list_move(&folio->_deferred_list, &list);
} else {
/* We lost race with folio_put() */
mod_mthp_stat(folio_order(folio), MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, -1);
list_del_init(&folio->_deferred_list);
ds_queue->split_queue_len--;
}