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

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: 68a1436bde00 ("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>

0 files changed, 0 insertions, 0 deletions