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mm/vmscan: avoid pointless large folio splits without swap

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When swap is disabled, exhausted, or unavailable due to memcg swap limits,
splitting a large anonymous folio cannot make swapout progress.  The
fallback only destroys the large folio and inflates split statistics.

Use -E2BIG from folio_alloc_swap() as the explicit signal that splitting
the folio might allow swapout of smaller pieces.  For other allocation
failures, keep the existing activation path and avoid the split.

This preserves the split fallback for fragmented or partially available
swap, while avoiding it when there is no backing space for any part of the
folio.

Link: https://lore.kernel.org/20260830042920.2280454-4-xueyuan.chen21@gmail.com
Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>
Signed-off-by: Xueyuan Chen <xueyuan.chen21@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reported-by: Nanzhe Zhao <zhaonanzhe@xiaomi.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Baoquan He <baoquan.he@linux.dev>
Cc: Chris Li <chrisl@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kairui Song <ryncsn@gmail.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Youngjun Park <youngjun.park@lge.com>
This commit is contained in:
Barry Song (Xiaomi) 2026-08-30 12:29:19 +08:00 committed by Andrew Morton
parent c50c376e1f
commit 696444530a
1 changed files with 6 additions and 1 deletions
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7
mm/vmscan.c
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@ -1259,6 +1259,8 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
*/
if (folio_test_anon(folio) && folio_test_swapbacked(folio) &&
!folio_test_swapcache(folio)) {
int ret;
if (!(sc->gfp_mask & __GFP_IO))
goto keep_locked;
if (folio_maybe_dma_pinned(folio))
@ -1277,11 +1279,14 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
split_folio_to_list(folio, folio_list))
goto activate_locked;
}
if (folio_alloc_swap(folio)) {
ret = folio_alloc_swap(folio);
if (ret) {
int __maybe_unused order = folio_order(folio);
if (!folio_test_large(folio))
goto activate_locked_split;
if (ret != -E2BIG)
goto activate_locked;
/* Fallback to swap normal pages */
if (split_folio_to_list(folio, folio_list))
goto activate_locked;