linux-kernel - [PATCH v2 2/2] mm: vmscan: simplify the folio refcount check in pageout()

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Message-ID: <4cbbec5bb92397aa4597105f1f499aabf7a1901c.1758166683.git.baolin.wang@linux.alibaba.com>
Date: Thu, 18 Sep 2025 11:46:54 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: akpm@...ux-foundation.org,
	hannes@...xchg.org
Cc: david@...hat.com,
	mhocko@...nel.org,
	zhengqi.arch@...edance.com,
	shakeel.butt@...ux.dev,
	lorenzo.stoakes@...cle.com,
	hughd@...gle.com,
	willy@...radead.org,
	baolin.wang@...ux.alibaba.com,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2 2/2] mm: vmscan: simplify the folio refcount check in pageout()

Since we no longer attempt to write back filesystem folios in pageout()
(they will be filtered out by the following check in pageout()), and only
tmpfs/shmem folios and anonymous swapcache folios can be written back,
we can remove the redundant folio_test_private() when checking the folio's
refcount, as tmpfs/shmem and swapcache folios do not use the PG_private flag.

While we're at it, we can open-code the folio refcount check instead of
adding a simple helper that has only one user.

Acked-by: David Hildenbrand <david@...hat.com>
Acked-by: Shakeel Butt <shakeel.butt@...ux.dev>
Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
---
 mm/vmscan.c | 16 ++++------------
 1 file changed, 4 insertions(+), 12 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 930add6d90ab..b3a57db6a445 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -477,17 +477,6 @@ static int reclaimer_offset(struct scan_control *sc)
 	return PGSTEAL_DIRECT - PGSTEAL_KSWAPD;
 }
 
-static inline int is_page_cache_freeable(struct folio *folio)
-{
-	/*
-	 * A freeable page cache folio is referenced only by the caller
-	 * that isolated the folio, the page cache and optional filesystem
-	 * private data at folio->private.
-	 */
-	return folio_ref_count(folio) - folio_test_private(folio) ==
-		1 + folio_nr_pages(folio);
-}
-
 /*
  * We detected a synchronous write error writing a folio out.  Probably
  * -ENOSPC.  We need to propagate that into the address_space for a subsequent
@@ -696,8 +685,11 @@ static pageout_t pageout(struct folio *folio, struct address_space *mapping,
 	 * block, for some throttling. This happens by accident, because
 	 * swap_backing_dev_info is bust: it doesn't reflect the
 	 * congestion state of the swapdevs.  Easy to fix, if needed.
+	 *
+	 * A freeable shmem or swapcache folio is referenced only by the
+	 * caller that isolated the folio and the page cache.
 	 */
-	if (!is_page_cache_freeable(folio))
+	if (folio_ref_count(folio) != 1 + folio_nr_pages(folio))
 		return PAGE_KEEP;
 	if (!mapping) {
 		/*
-- 
2.43.7