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   1 From 4f78252da887ee7e9d1875dd6e07d9baa936c04f Mon Sep 17 00:00:00 2001
   2 From: Kemeng Shi <shikemeng@huaweicloud.com>
   3 Date: Thu, 22 May 2025 20:25:51 +0800
   4 Subject: mm: swap: move nr_swap_pages counter decrement from folio_alloc_swap() to swap_range_alloc()
   5
   6 From: Kemeng Shi <shikemeng@huaweicloud.com>
   7
   8 commit 4f78252da887ee7e9d1875dd6e07d9baa936c04f upstream.
   9
  10 Patch series "Some randome fixes and cleanups to swapfile".
  11
  12 Patch 0-3 are some random fixes.  Patch 4 is a cleanup.  More details can
  13 be found in respective patches.
  14
  15
  16 This patch (of 4):
  17
  18 When folio_alloc_swap() encounters a failure in either
  19 mem_cgroup_try_charge_swap() or add_to_swap_cache(), nr_swap_pages counter
  20 is not decremented for allocated entry.  However, the following
  21 put_swap_folio() will increase nr_swap_pages counter unpairly and lead to
  22 an imbalance.
  23
  24 Move nr_swap_pages decrement from folio_alloc_swap() to swap_range_alloc()
  25 to pair the nr_swap_pages counting.
  26
  27 Link: https://lkml.kernel.org/r/20250522122554.12209-1-shikemeng@huaweicloud.com
  28 Link: https://lkml.kernel.org/r/20250522122554.12209-2-shikemeng@huaweicloud.com
  29 Fixes: 0ff67f990bd4 ("mm, swap: remove swap slot cache")
  30 Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
  31 Reviewed-by: Kairui Song <kasong@tencent.com>
  32 Reviewed-by: Baoquan He <bhe@redhat.com>
  33 Cc: Johannes Weiner <hannes@cmpxchg.org>
  34 Cc: <stable@vger.kernel.org>
  35 Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
  36 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  37 ---
  38  mm/swapfile.c |    2 +-
  39  1 file changed, 1 insertion(+), 1 deletion(-)
  40
  41 --- a/mm/swapfile.c
  42 +++ b/mm/swapfile.c
  43 @@ -1115,6 +1115,7 @@ static void swap_range_alloc(struct swap
  44                 if (vm_swap_full())
  45                         schedule_work(&si->reclaim_work);
  46         }
  47 +       atomic_long_sub(nr_entries, &nr_swap_pages);
  48  }
  49
  50  static void swap_range_free(struct swap_info_struct *si, unsigned long offset,
  51 @@ -1313,7 +1314,6 @@ int folio_alloc_swap(struct folio *folio
  52         if (add_to_swap_cache(folio, entry, gfp | __GFP_NOMEMALLOC, NULL))
  53                 goto out_free;
  54
  55 -       atomic_long_sub(size, &nr_swap_pages);
  56         return 0;
  57
  58  out_free: