+ mm-fix-duplicate-accounting-of-free-pages-in-should_reclaim_retry.patch added to mm-new branch

+ mm-fix-duplicate-accounting-of-free-pages-in-should_reclaim_retry.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: mm: fix duplicate accounting of free pages in should_reclaim_retry()
has been added to the -mm mm-new branch.  Its filename is
     mm-fix-duplicate-accounting-of-free-pages-in-should_reclaim_retry.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-fix-duplicate-accounting-of-free-pages-in-should_reclaim_retry.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
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fixup patches in mm-new.

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------------------------------------------------------
From: liuqiqi <liuqiqi@kylinos.cn>
Subject: mm: fix duplicate accounting of free pages in should_reclaim_retry()
Date: Tue, 12 Aug 2025 15:02:10 +0800

In the zone_reclaimable_pages() function, if the page counts for
NR_ZONE_INACTIVE_FILE, NR_ZONE_ACTIVE_FILE, NR_ZONE_INACTIVE_ANON, and
NR_ZONE_ACTIVE_ANON are all zero, the function returns the number of free
pages as the result.

In this case, when should_reclaim_retry() calculates reclaimable pages, it
will inadvertently double-count the free pages in its accounting.

static inline bool
should_reclaim_retry(gfp_t gfp_mask, unsigned order,
                     struct alloc_context *ac, int alloc_flags,
                     bool did_some_progress, int *no_progress_loops)
{
        ...
                available = reclaimable = zone_reclaimable_pages(zone);
                available += zone_page_state_snapshot(zone, NR_FREE_PAGES);

Link: https://lkml.kernel.org/r/20250812070210.1624218-1-liuqiqi@kylinos.cn
Signed-off-by: liuqiqi <liuqiqi@kylinos.cn>
Cc: David Hildenbrand <david@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/vmscan.c |   11 ++---------
 1 file changed, 2 insertions(+), 9 deletions(-)

--- a/mm/vmscan.c~mm-fix-duplicate-accounting-of-free-pages-in-should_reclaim_retry
+++ a/mm/vmscan.c
@@ -398,14 +398,7 @@ unsigned long zone_reclaimable_pages(str
 	if (can_reclaim_anon_pages(NULL, zone_to_nid(zone), NULL))
 		nr += zone_page_state_snapshot(zone, NR_ZONE_INACTIVE_ANON) +
 			zone_page_state_snapshot(zone, NR_ZONE_ACTIVE_ANON);
-	/*
-	 * If there are no reclaimable file-backed or anonymous pages,
-	 * ensure zones with sufficient free pages are not skipped.
-	 * This prevents zones like DMA32 from being ignored in reclaim
-	 * scenarios where they can still help alleviate memory pressure.
-	 */
-	if (nr == 0)
-		nr = zone_page_state_snapshot(zone, NR_FREE_PAGES);
+
 	return nr;
 }
 
@@ -6495,7 +6488,7 @@ static bool allow_direct_reclaim(pg_data
 		return true;
 
 	for_each_managed_zone_pgdat(zone, pgdat, i, ZONE_NORMAL) {
-		if (!zone_reclaimable_pages(zone))
+		if (!zone_reclaimable_pages(zone) && zone_page_state_snapshot(zone, NR_FREE_PAGES))
 			continue;
 
 		pfmemalloc_reserve += min_wmark_pages(zone);
_

Patches currently in -mm which might be from liuqiqi@kylinos.cn are

mm-fix-duplicate-accounting-of-free-pages-in-should_reclaim_retry.patch