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

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Message-ID: <e475c5ddbb94763b12d396122ade8ee3c711a967.1757648598.git.baolin.wang@linux.alibaba.com>
Date: Fri, 12 Sep 2025 11:45:08 +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 2/2] mm: vmscan: simplify the folio refcount check in pageout()

Since we no longer attempt to write back filesystem folios 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.

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 8056fccb9cc4..46baaadc528d 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) || !mapping)
+	if (folio_ref_count(folio) != 1 + folio_nr_pages(folio) || !mapping)
 		return PAGE_KEEP;
 
 	if (!shmem_mapping(mapping) && !folio_test_anon(folio))
-- 
2.43.7