The patch titled
Subject: mm: vmscan: avoid split during shrink_folio_list()
has been added to the -mm mm-unstable branch. Its filename is
mm-vmscan-avoid-split-during-shrink_folio_list.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-vmscan-avoid-split-during-shrink_folio_list.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: Ryan Roberts <ryan.roberts@xxxxxxx>
Subject: mm: vmscan: avoid split during shrink_folio_list()
Date: Wed, 3 Apr 2024 12:40:31 +0100
Now that swap supports storing all mTHP sizes, avoid splitting large
folios before swap-out. This benefits performance of the swap-out path by
eliding split_folio_to_list(), which is expensive, and also sets us up for
swapping in large folios in a future series.
If the folio is partially mapped, we continue to split it since we want to
avoid the extra IO overhead and storage of writing out pages
uneccessarily.
THP_SWPOUT and THP_SWPOUT_FALLBACK counters should continue to count
events only for PMD-mappable folios to avoid user confusion. THP_SWPOUT
already has the appropriate guard. Add a guard for THP_SWPOUT_FALLBACK.
It may be appropriate to add per-size counters in future.
Link: https://lkml.kernel.org/r/20240403114032.1162100-6-ryan.roberts@xxxxxxx
Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx>
Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
Reviewed-by: Barry Song <v-songbaohua@xxxxxxxx>
Cc: Barry Song <21cnbao@xxxxxxxxx>
Cc: Chris Li <chrisl@xxxxxxxxxx>
Cc: Gao Xiang <xiang@xxxxxxxxxx>
Cc: "Huang, Ying" <ying.huang@xxxxxxxxx>
Cc: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
Cc: Lance Yang <ioworker0@xxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Yang Shi <shy828301@xxxxxxxxx>
Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/vmscan.c | 17 +++++++++++------
1 file changed, 11 insertions(+), 6 deletions(-)
--- a/mm/vmscan.c~mm-vmscan-avoid-split-during-shrink_folio_list
+++ a/mm/vmscan.c
@@ -1206,11 +1206,12 @@ retry:
if (!can_split_folio(folio, NULL))
goto activate_locked;
/*
- * Split folios without a PMD map right
- * away. Chances are some or all of the
- * tail pages can be freed without IO.
+ * Split partially mapped folios right
+ * away. We can free the unmapped pages
+ * without IO.
*/
- if (!folio_entire_mapcount(folio) &&
+ if (data_race(!list_empty(
+ &folio->_deferred_list)) &&
split_folio_to_list(folio,
folio_list))
goto activate_locked;
@@ -1223,8 +1224,12 @@ retry:
folio_list))
goto activate_locked;
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
- count_memcg_folio_events(folio, THP_SWPOUT_FALLBACK, 1);
- count_vm_event(THP_SWPOUT_FALLBACK);
+ if (nr_pages >= HPAGE_PMD_NR) {
+ count_memcg_folio_events(folio,
+ THP_SWPOUT_FALLBACK, 1);
+ count_vm_event(
+ THP_SWPOUT_FALLBACK);
+ }
#endif
if (!add_to_swap(folio))
goto activate_locked_split;
_
Patches currently in -mm which might be from ryan.roberts@xxxxxxx are
mm-swap-remove-cluster_flag_huge-from-swap_cluster_info-flags.patch
mm-swap-free_swap_and_cache_nr-as-batched-free_swap_and_cache.patch
mm-swap-simplify-struct-percpu_cluster.patch
mm-swap-allow-storage-of-all-mthp-orders.patch
mm-vmscan-avoid-split-during-shrink_folio_list.patch
mm-madvise-avoid-split-during-madv_pageout-and-madv_cold.patch
mm-madvise-avoid-split-during-madv_pageout-and-madv_cold-fix.patch
