linux-kernel - [PATCH 1/2] madvise: don't use mapcount() against large folio for sharing check

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Message-Id: <20230728161356.1784568-2-fengwei.yin@intel.com>
Date:   Sat, 29 Jul 2023 00:13:55 +0800
From:   Yin Fengwei <fengwei.yin@...el.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org, akpm@...ux-foundation.org,
        willy@...radead.org, vishal.moola@...il.com,
        wangkefeng.wang@...wei.com, minchan@...nel.org, yuzhao@...gle.com,
        david@...hat.com, ryan.roberts@....com, shy828301@...il.com
Cc:     fengwei.yin@...el.com
Subject: [PATCH 1/2] madvise: don't use mapcount() against large folio for sharing check

The 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.

Fixes: 07e8c82b5eff ("madvise: convert madvise_cold_or_pageout_pte_range() to use folios")
Signed-off-by: Yin Fengwei <fengwei.yin@...el.com>
Reviewed-by: Yu Zhao <yuzhao@...gle.com>
---
 mm/madvise.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/madvise.c b/mm/madvise.c
index 886f06066622..148b46beb039 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -383,7 +383,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
 		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))
@@ -457,7 +457,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
 		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;
-- 
2.39.2