+ madvise-madvise_free_pte_range-dont-use-mapcount-against-large-folio-for-sharing-check.patch added to mm-hotfixes-unstable branch

+ madvise-madvise_free_pte_range-dont-use-mapcount-against-large-folio-for-sharing-check.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

The patch titled
     Subject: madvise:madvise_free_pte_range(): don't use mapcount() against large folio for sharing check
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     madvise-madvise_free_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_free_pte_range-dont-use-mapcount-against-large-folio-for-sharing-check.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Yin Fengwei <fengwei.yin@intel.com>
Subject: madvise:madvise_free_pte_range(): don't use mapcount() against large folio for sharing check
Date: Tue, 8 Aug 2023 10:09:17 +0800

Commit 98b211d6415f ("madvise: convert madvise_free_pte_range() to use a
folio") replaced the page_mapcount() with folio_mapcount() to check
whether the folio is shared by other mapping.

It's not correct for large folios. 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. It should be OK for madvise case here.

User-visible effects is that the THP is skipped when user call madvise.
But the correct behavior is THP should be split and processed then.

NOTE: this change is a temporary fix to reduce the user-visible effects
before the long term fix from David is ready.

Link: https://lkml.kernel.org/r/20230808020917.2230692-4-fengwei.yin@intel.com
Fixes: 98b211d6415f ("madvise: convert madvise_free_pte_range() to use a folio")
Signed-off-by: Yin Fengwei <fengwei.yin@intel.com>
Reviewed-by: Yu Zhao <yuzhao@google.com>
Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/madvise.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/madvise.c~madvise-madvise_free_pte_range-dont-use-mapcount-against-large-folio-for-sharing-check
+++ a/mm/madvise.c
@@ -680,7 +680,7 @@ static int madvise_free_pte_range(pmd_t
 		if (folio_test_large(folio)) {
 			int err;
 
-			if (folio_mapcount(folio) != 1)
+			if (folio_estimated_sharers(folio) != 1)
 				break;
 			if (!folio_trylock(folio))
 				break;
_

Patches currently in -mm which might be from fengwei.yin@intel.com 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
filemap-add-filemap_map_folio_range.patch
rmap-add-folio_add_file_rmap_range.patch
mm-convert-do_set_pte-to-set_pte_range.patch
filemap-batch-pte-mappings.patch