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mm/vmscan: fix anon-only reclaim evicting file pages when swappiness=max

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Patch series "mm/vmscan: fix swappiness=max and clean up per-node
proactive reclaim", v4.

Fixes and one cleanup.

Patch 1 fixes "swappiness=max": the anon-only test in get_scan_count() sat
after the "cannot reclaim anon" check, so when no anon was reclaimable the
request fell back to SCAN_FILE and evicted page cache instead.

Patch 2 fixes reclaim_store() collapsing every error into -EAGAIN, so
callers can no longer tell an invalid argument from a busy interface;
propagate the real error code, matching the memcg path.

Patch 3 drops the now-unused gfp_mask parameter from __node_reclaim().

Patch 4 fixes the same "swappiness=max" issue for MGLRU.


This patch (of 4):

As Qi mentioned [1], when swappiness=max (SWAPPINESS_ANON_ONLY) is set,
the reclaim logic is expected to reclaim anonymous pages exclusively. 
However, due to the current ordering of checks in get_scan_count(), file
pages may still be evicted if can_reclaim_anon_pages() returns false,
which contradicts the semantics of SWAPPINESS_ANON_ONLY.

Reproducer in a cgroup holding 64M of file cache, with no swap configured:

  Before (file cache is wrongly evicted):
    # cat memory.stat
    anon 196608
    file 67178496
    pgscan_proactive 0
    # echo "64M swappiness=max" > memory.reclaim
    # cat memory.stat
    anon 208896
    file 4096                 <- page cache evicted
    pgsteal_proactive 16400
    pgscan_proactive 16400

  After (file cache is left intact):
    # cat memory.stat
    anon 200704
    file 67178496
    pgscan_proactive 0
    # echo "64M swappiness=max" > memory.reclaim
    -bash: echo: write error: Resource temporarily unavailable
    # cat memory.stat
    anon 208896
    file 67178496             <- page cache untouched
    pgsteal_proactive 0
    pgscan_proactive 0

Fix this by bailing out early when SWAPPINESS_ANON_ONLY is set and no
anonymous pages are reclaimable, before falling back to file reclaim.

Link: https://lore.kernel.org/20260724033435.2573323-1-ridong.chen@linux.dev
Link: https://lore.kernel.org/20260724033435.2573323-2-ridong.chen@linux.dev
Link: https://lore.kernel.org/cgroups/7ddf3eee-5fe2-45f7-8614-c8936a039e04@linux.dev/ [1]
Fixes: 68a1436bde ("mm: add swappiness=max arg to memory.reclaim for only anon reclaim")
Signed-off-by: Ridong Chen <chenridong@xiaomi.com>
Suggested-by: Qi Zheng <qi.zheng@linux.dev>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Muchun Song <muchun.song@linux.dev>
Reviewed-by: Qi Zheng <qi.zheng@linux.dev>
Reviewed-by: Barry Song <baohua@kernel.org>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Kairui Song <kasong@tencent.com>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Wei Xu <weixugc@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Cc: Zhongkun He <hezhongkun.hzk@bytedance.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Ridong Chen
2026-07-24 11:34:32 +08:00
committed by Andrew Morton
parent e474ac24a7
commit e26f7a91de
1 changed files with 17 additions and 7 deletions
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24
mm/vmscan.c
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@@ -2494,6 +2494,23 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
enum scan_balance scan_balance;
enum lru_list lru;
/*
* Proactive reclaim initiated by userspace for anonymous memory only.
* SWAPPINESS_ANON_ONLY is set only on the proactive reclaim path, so
* warn if it shows up elsewhere. When anon cannot be reclaimed (e.g.
* no swap), bail out instead of falling back to evicting file pages,
* which would violate the anon-only semantics.
*/
if (swappiness == SWAPPINESS_ANON_ONLY) {
WARN_ON_ONCE(!sc->proactive);
if (!can_reclaim_anon_pages(memcg, pgdat->node_id, sc)) {
memset(nr, 0, sizeof(*nr) * NR_LRU_LISTS);
return;
}
scan_balance = SCAN_ANON;
goto out;
}
/* If we have no swap space, do not bother scanning anon folios. */
if (!sc->may_swap || !can_reclaim_anon_pages(memcg, pgdat->node_id, sc)) {
scan_balance = SCAN_FILE;
@@ -2512,13 +2529,6 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
goto out;
}
/* Proactive reclaim initiated by userspace for anonymous memory only */
if (swappiness == SWAPPINESS_ANON_ONLY) {
WARN_ON_ONCE(!sc->proactive);
scan_balance = SCAN_ANON;
goto out;
}
/*
* Do not apply any pressure balancing cleverness when the
* system is close to OOM, scan both anon and file equally