The patch titled
Subject: mm: count the number of partially mapped anonymous THPs per size
has been added to the -mm mm-unstable branch. Its filename is
mm-count-the-number-of-partially-mapped-anonymous-thps-per-size.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-count-the-number-of-partially-mapped-anonymous-thps-per-size.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Barry Song <v-songbaohua@xxxxxxxx>
Subject: mm: count the number of partially mapped anonymous THPs per size
Date: Sat, 24 Aug 2024 13:04:41 +1200
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@xxxxxxxxx
Signed-off-by: Barry Song <v-songbaohua@xxxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Cc: Chris Li <chrisl@xxxxxxxxxx>
Cc: Chuanhua Han <hanchuanhua@xxxxxxxx>
Cc: Kairui Song <kasong@xxxxxxxxxxx>
Cc: Kalesh Singh <kaleshsingh@xxxxxxxxxx>
Cc: Lance Yang <ioworker0@xxxxxxxxx>
Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
Cc: Shuai Yuan <yuanshuai@xxxxxxxx>
Cc: Usama Arif <usamaarif642@xxxxxxxxx>
Cc: Zi Yan <ziy@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/admin-guide/mm/transhuge.rst | 7 +++++++
include/linux/huge_mm.h | 1 +
mm/huge_memory.c | 6 ++++++
3 files changed, 14 insertions(+)
--- a/Documentation/admin-guide/mm/transhuge.rst~mm-count-the-number-of-partially-mapped-anonymous-thps-per-size
+++ a/Documentation/admin-guide/mm/transhuge.rst
@@ -556,6 +556,13 @@ nr_anon
These huge pages could be 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
--- a/include/linux/huge_mm.h~mm-count-the-number-of-partially-mapped-anonymous-thps-per-size
+++ a/include/linux/huge_mm.h
@@ -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
};
--- a/mm/huge_memory.c~mm-count-the-number-of-partially-mapped-anonymous-thps-per-size
+++ a/mm/huge_memory.c
@@ -598,6 +598,7 @@ DEFINE_MTHP_STAT_ATTR(split, MTHP_STAT_S
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,
@@ -611,6 +612,7 @@ static struct attribute *anon_stats_attr
&split_failed_attr.attr,
&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(str
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
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 *
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
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--;
}
_
Patches currently in -mm which might be from v-songbaohua@xxxxxxxx are
mm-extend-usage-parameter-so-that-cluster_swap_free_nr-can-be-reused.patch
mm-swap-add-nr-argument-in-swapcache_prepare-and-swapcache_clear-to-support-large-folios.patch
mm-swap-add-nr-argument-in-swapcache_prepare-and-swapcache_clear-to-support-large-folios-fix.patch
vpda-try-to-fix-the-potential-crash-due-to-misusing-__gfp_nofail.patch
mm-document-__gfp_nofail-must-be-blockable.patch
mm-bug_on-to-avoid-null-deference-while-__gfp_nofail-fails.patch
mm-prohibit-null-deference-exposed-for-unsupported-non-blockable-__gfp_nofail.patch
mm-rename-instances-of-swap_info_struct-to-meaningful-si.patch
mm-attempt-to-batch-free-swap-entries-for-zap_pte_range.patch
mm-attempt-to-batch-free-swap-entries-for-zap_pte_range-fix.patch
mm-override-mthp-enabled-defaults-at-kernel-cmdline-fix.patch
mm-count-the-number-of-anonymous-thps-per-size.patch
mm-count-the-number-of-partially-mapped-anonymous-thps-per-size.patch
