linux-kernel - [PATCH v2] mm/vmscan: don't try to reclaim freed folios

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Date:   Wed, 8 Jun 2022 22:14:32 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     <akpm@...ux-foundation.org>
CC:     <willy@...radead.org>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>, <linmiaohe@...wei.com>
Subject: [PATCH v2] mm/vmscan: don't try to reclaim freed folios

If folios were freed from under us, there's no need to reclaim them. Skip
these folios to save lots of cpu cycles and avoid possible unnecessary
disk I/O.

Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
---
v2:
  use folio_ref_freeze to guard against race with GUP (fast). Many thanks
  Matthew for pointing this out.
---
 mm/vmscan.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 13d34d9593bb..547ae7ae6ab1 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1610,13 +1610,19 @@ static unsigned int shrink_page_list(struct list_head *page_list,
 		folio = lru_to_folio(page_list);
 		list_del(&folio->lru);
 
+		nr_pages = folio_nr_pages(folio);
+
+		if (folio_ref_count(folio) == 1 &&
+		    folio_ref_freeze(folio, 1)) {
+			/* folio was freed from under us. So we are done. */
+			goto free_it;
+		}
+
 		if (!folio_trylock(folio))
 			goto keep;
 
 		VM_BUG_ON_FOLIO(folio_test_active(folio), folio);
 
-		nr_pages = folio_nr_pages(folio);
-
 		/* Account the number of base pages */
 		sc->nr_scanned += nr_pages;
 
-- 
2.23.0