linux-kernel - [PATCH 6.6.y 1/7] mm: memcg: add THP swap out info for anonymous reclaim

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Message-ID: <20251103075135.20254-2-leon.huangfu@shopee.com>
Date: Mon,  3 Nov 2025 15:51:29 +0800
From: Leon Huang Fu <leon.huangfu@...pee.com>
To: stable@...r.kernel.org,
	greg@...ah.com
Cc: tj@...nel.org,
	lizefan.x@...edance.com,
	hannes@...xchg.org,
	corbet@....net,
	mhocko@...nel.org,
	roman.gushchin@...ux.dev,
	shakeelb@...gle.com,
	muchun.song@...ux.dev,
	akpm@...ux-foundation.org,
	sjenning@...hat.com,
	ddstreet@...e.org,
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	leon.huangfu@...pee.com,
	shy828301@...il.com,
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	vishal.moola@...il.com,
	cerasuolodomenico@...il.com,
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	cgroups@...r.kernel.org,
	linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	Xin Hao <vernhao@...cent.com>,
	Michal Hocko <mhocko@...e.com>,
	Muchun Song <songmuchun@...edance.com>
Subject: [PATCH 6.6.y 1/7] mm: memcg: add THP swap out info for anonymous reclaim

From: Xin Hao <vernhao@...cent.com>

[ Upstream commit 811244a501b967b00fecb1ae906d5dc6329c91e0 ]

At present, we support per-memcg reclaim strategy, however we do not know
the number of transparent huge pages being reclaimed, as we know the
transparent huge pages need to be splited before reclaim them, and they
will bring some performance bottleneck effect.  for example, when two
memcg (A & B) are doing reclaim for anonymous pages at same time, and 'A'
memcg is reclaiming a large number of transparent huge pages, we can
better analyze that the performance bottleneck will be caused by 'A'
memcg.  therefore, in order to better analyze such problems, there add THP
swap out info for per-memcg.

[akpm@...ux-foundation.orgL fix swap_writepage_fs(), per Johannes]
  Link: https://lkml.kernel.org/r/20230913213343.GB48476@cmpxchg.org
Link: https://lkml.kernel.org/r/20230913164938.16918-1-vernhao@tencent.com
Signed-off-by: Xin Hao <vernhao@...cent.com>
Suggested-by: Johannes Weiner <hannes@...xchg.org>
Acked-by: Johannes Weiner <hannes@...xchg.org>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Roman Gushchin <roman.gushchin@...ux.dev>
Cc: Shakeel Butt <shakeelb@...gle.com>
Cc: Muchun Song <songmuchun@...edance.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Leon Huang Fu <leon.huangfu@...pee.com>
---
 Documentation/admin-guide/cgroup-v2.rst | 9 +++++++++
 mm/memcontrol.c                         | 2 ++
 mm/page_io.c                            | 8 ++++----
 mm/vmscan.c                             | 1 +
 4 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index b26b5274eaaf..622a7f28db1f 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -1532,6 +1532,15 @@ PAGE_SIZE multiple when read back.
 		collapsing an existing range of pages. This counter is not
 		present when CONFIG_TRANSPARENT_HUGEPAGE is not set.

+	  thp_swpout (npn)
+		Number of transparent hugepages which are swapout in one piece
+		without splitting.
+
+	  thp_swpout_fallback (npn)
+		Number of transparent hugepages which were split before swapout.
+		Usually because failed to allocate some continuous swap space
+		for the huge page.
+
   memory.numa_stat
 	A read-only nested-keyed file which exists on non-root cgroups.

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 2d2cada8a8a4..c61c90ea72a4 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -704,6 +704,8 @@ static const unsigned int memcg_vm_event_stat[] = {
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 	THP_FAULT_ALLOC,
 	THP_COLLAPSE_ALLOC,
+	THP_SWPOUT,
+	THP_SWPOUT_FALLBACK,
 #endif
 };

diff --git a/mm/page_io.c b/mm/page_io.c
index fe4c21af23f2..cb559ae324c6 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -208,8 +208,10 @@ int swap_writepage(struct page *page, struct writeback_control *wbc)
 static inline void count_swpout_vm_event(struct folio *folio)
 {
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	if (unlikely(folio_test_pmd_mappable(folio)))
+	if (unlikely(folio_test_pmd_mappable(folio))) {
+		count_memcg_folio_events(folio, THP_SWPOUT, 1);
 		count_vm_event(THP_SWPOUT);
+	}
 #endif
 	count_vm_events(PSWPOUT, folio_nr_pages(folio));
 }
@@ -278,9 +280,6 @@ static void sio_write_complete(struct kiocb *iocb, long ret)
 			set_page_dirty(page);
 			ClearPageReclaim(page);
 		}
-	} else {
-		for (p = 0; p < sio->pages; p++)
-			count_swpout_vm_event(page_folio(sio->bvec[p].bv_page));
 	}

 	for (p = 0; p < sio->pages; p++)
@@ -296,6 +295,7 @@ static void swap_writepage_fs(struct page *page, struct writeback_control *wbc)
 	struct file *swap_file = sis->swap_file;
 	loff_t pos = page_file_offset(page);

+	count_swpout_vm_event(page_folio(page));
 	set_page_writeback(page);
 	unlock_page(page);
 	if (wbc->swap_plug)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 258f5472f1e9..774bae2f54d7 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1922,6 +1922,7 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
 								folio_list))
 						goto activate_locked;
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
+					count_memcg_folio_events(folio, THP_SWPOUT_FALLBACK, 1);
 					count_vm_event(THP_SWPOUT_FALLBACK);
 #endif
 					if (!add_to_swap(folio))
--
2.50.1