linux-kernel - [PATCH 1/4] mm: swap: move nr_swap_pages counter decrement from folio_alloc_swap() to swap_range

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Message-Id: <20250522122554.12209-2-shikemeng@huaweicloud.com>
Date: Thu, 22 May 2025 20:25:51 +0800
From: Kemeng Shi <shikemeng@...weicloud.com>
To: akpm@...ux-foundation.org
Cc: kasong@...cent.com,
	bhe@...hat.com,
	hannes@...xchg.org,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 1/4] mm: swap: move nr_swap_pages counter decrement from folio_alloc_swap() to swap_range_alloc()

When folio_alloc_swap() encounters a failure in either
mem_cgroup_try_charge_swap() or add_to_swap_cache(), nr_swap_pages counter
is not decremented for allocated entry. However, the following
put_swap_folio() will increase nr_swap_pages counter unpairly and lead to
an imbalance.

Move nr_swap_pages decrement from folio_alloc_swap() to swap_range_alloc()
to pair the nr_swap_pages counting.

Fixes: 0ff67f990bd45 ("mm, swap: remove swap slot cache")
Signed-off-by: Kemeng Shi <shikemeng@...weicloud.com>
---
 mm/swapfile.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 026090bf3efe..75b69213c2e7 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1115,6 +1115,7 @@ static void swap_range_alloc(struct swap_info_struct *si,
 		if (vm_swap_full())
 			schedule_work(&si->reclaim_work);
 	}
+	atomic_long_sub(nr_entries, &nr_swap_pages);
 }
 
 static void swap_range_free(struct swap_info_struct *si, unsigned long offset,
@@ -1313,7 +1314,6 @@ int folio_alloc_swap(struct folio *folio, gfp_t gfp)
 	if (add_to_swap_cache(folio, entry, gfp | __GFP_NOMEMALLOC, NULL))
 		goto out_free;
 
-	atomic_long_sub(size, &nr_swap_pages);
 	return 0;
 
 out_free:
-- 
2.30.0