Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   Yin Fengwei <fengwei.yin@intel.com>
To:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        stable@vger.kernel.org, akpm@linux-foundation.org,
        willy@infradead.org, vishal.moola@gmail.com,
        wangkefeng.wang@huawei.com, minchan@kernel.org, yuzhao@google.com,
        david@redhat.com, ryan.roberts@arm.com, shy828301@gmail.com
Cc:     fengwei.yin@intel.com
Subject: [PATCH 1/2] madvise: don't use mapcount() against large folio for sharing check
Date:   Sat, 29 Jul 2023 00:13:55 +0800
Message-Id: <20230728161356.1784568-2-fengwei.yin@intel.com>
In-Reply-To: <20230728161356.1784568-1-fengwei.yin@intel.com>
References: <20230728161356.1784568-1-fengwei.yin@intel.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

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@intel.com>
Reviewed-by: Yu Zhao <yuzhao@google.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