linux-kernel - [PATCH v1 11/18] mm/migrate: use folio_likely_mapped_shared() in add_page_for

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Message-ID: <20240409192301.907377-12-david@redhat.com>
Date: Tue,  9 Apr 2024 21:22:54 +0200
From: David Hildenbrand <david@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org,
	linux-doc@...r.kernel.org,
	cgroups@...r.kernel.org,
	linux-sh@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	David Hildenbrand <david@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Matthew Wilcox (Oracle)" <willy@...radead.org>,
	Peter Xu <peterx@...hat.com>,
	Ryan Roberts <ryan.roberts@....com>,
	Yin Fengwei <fengwei.yin@...el.com>,
	Yang Shi <shy828301@...il.com>,
	Zi Yan <ziy@...dia.com>,
	Jonathan Corbet <corbet@....net>,
	Hugh Dickins <hughd@...gle.com>,
	Yoshinori Sato <ysato@...rs.sourceforge.jp>,
	Rich Felker <dalias@...c.org>,
	John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
	Chris Zankel <chris@...kel.net>,
	Max Filippov <jcmvbkbc@...il.com>,
	Muchun Song <muchun.song@...ux.dev>,
	Miaohe Lin <linmiaohe@...wei.com>,
	Naoya Horiguchi <naoya.horiguchi@....com>,
	Richard Chang <richardycc@...gle.com>
Subject: [PATCH v1 11/18] mm/migrate: use folio_likely_mapped_shared() in add_page_for_migration()

We want to limit the use of page_mapcount() to the places where it is
absolutely necessary. In add_page_for_migration(), we actually want to
check if the folio is mapped shared, to reject such folios. So let's
use folio_likely_mapped_shared() instead.

For small folios, fully mapped THP, and hugetlb folios, there is no change.
For partially mapped, shared THP, we should now do a better job at
rejecting such folios.

Signed-off-by: David Hildenbrand <david@...hat.com>
---
 mm/migrate.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 285072bca29c..d87ce32645d4 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2140,7 +2140,7 @@ static int add_page_for_migration(struct mm_struct *mm, const void __user *p,
 		goto out_putfolio;
 
 	err = -EACCES;
-	if (page_mapcount(page) > 1 && !migrate_all)
+	if (folio_likely_mapped_shared(folio) && !migrate_all)
 		goto out_putfolio;
 
 	err = -EBUSY;
-- 
2.44.0