+ mm-vmscan-avoid-split-during-shrink_folio_list.patch added to mm-unstable branch

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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, 27 Mar 2024 14:45:36 +0000

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.

Link: https://lkml.kernel.org/r/20240327144537.4165578-6-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 |    9 +++++----
 1 file changed, 5 insertions(+), 4 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;
_

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





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