The patch titled
Subject: madvise:madvise_cold_or_pageout_pte_range(): don't use mapcount() against large folio for sharing check
has been added to the -mm mm-unstable branch. Its filename is
madvise-madvise_cold_or_pageout_pte_range-dont-use-mapcount-against-large-folio-for-sharing-check.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/madvise-madvise_cold_or_pageout_pte_range-dont-use-mapcount-against-large-folio-for-sharing-check.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: Yin Fengwei <fengwei.yin@xxxxxxxxx>
Subject: madvise:madvise_cold_or_pageout_pte_range(): don't use mapcount() against large folio for sharing check
Date: Sat, 29 Jul 2023 00:13:55 +0800
Patch series "don't use mapcount() to check large folio sharing".
In madvise_cold_or_pageout_pte_range() and madvise_free_pte_range(),
folio_mapcount() is used to check whether the folio is shared. But it's
not correct as folio_mapcount() returns total mapcount of large folio.
Use folio_estimated_sharers() here as the estimated number is enough.
This patch (of 3):
Commit 07e8c82b5eff ("madvise: convert madvise_cold_or_pageout_pte_range()
to use folios") replaced the page_mapcount() with folio_mapcount() to
check whether the folio is shared by other mapping.
But it's not correct for large folio. folio_mapcount() returns the total
mapcount of large folio which is not suitable to detect whether the folio
is shared.
Use folio_estimated_sharers() which returns a estimated number of shares.
That means it's not 100% correct. But it should be OK for madvise case
here.
Link: https://lkml.kernel.org/r/20230728161356.1784568-1-fengwei.yin@xxxxxxxxx
Link: https://lkml.kernel.org/r/20230728161356.1784568-2-fengwei.yin@xxxxxxxxx
Fixes: 07e8c82b5eff ("madvise: convert madvise_cold_or_pageout_pte_range() to use folios")
Signed-off-by: Yin Fengwei <fengwei.yin@xxxxxxxxx>
Reviewed-by: Yu Zhao <yuzhao@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
Cc: Vishal Moola (Oracle) <vishal.moola@xxxxxxxxx>
Cc: Yang Shi <shy828301@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/madvise.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
--- a/mm/madvise.c~madvise-madvise_cold_or_pageout_pte_range-dont-use-mapcount-against-large-folio-for-sharing-check
+++ a/mm/madvise.c
@@ -383,7 +383,7 @@ static int madvise_cold_or_pageout_pte_r
folio = pfn_folio(pmd_pfn(orig_pmd));
/* Do not interfere with other mappings of this folio */
- if (folio_mapcount(folio) != 1)
+ if (folio_estimated_sharers(folio) != 1)
goto huge_unlock;
if (pageout_anon_only_filter && !folio_test_anon(folio))
@@ -459,7 +459,7 @@ regular_folio:
if (folio_test_large(folio)) {
int err;
- if (folio_mapcount(folio) != 1)
+ if (folio_estimated_sharers(folio) != 1)
break;
if (pageout_anon_only_filter && !folio_test_anon(folio))
break;
_
Patches currently in -mm which might be from fengwei.yin@xxxxxxxxx are
madvise-madvise_cold_or_pageout_pte_range-dont-use-mapcount-against-large-folio-for-sharing-check.patch
madvise-madvise_free_huge_pmd-dont-use-mapcount-against-large-folio-for-sharing-check.patch
madvise-madvise_free_pte_range-dont-use-mapcount-against-large-folio-for-sharing-check.patch
