From: Shakeel Butt <shakeel.butt@linux.dev>
To: Ridong <ridong.chen@linux.dev>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Kairui Song <kasong@tencent.com>, Qi Zheng <qi.zheng@linux.dev>,
Barry Song <baohua@kernel.org>,
Axel Rasmussen <axelrasmussen@google.com>,
Yuanchu Xie <yuanchu@google.com>, Wei Xu <weixugc@google.com>,
David Hildenbrand <david@kernel.org>,
Michal Hocko <mhocko@kernel.org>,
Lorenzo Stoakes <ljs@kernel.org>,
Zhongkun He <hezhongkun.hzk@bytedance.com>,
Muchun Song <muchun.song@linux.dev>,
Davidlohr Bueso <dave@stgolabs.net>,
Roman Gushchin <roman.gushchin@linux.dev>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Ridong Chen <chenridong@xiaomi.com>
Subject: Re: [PATCH 1/3] mm/vmscan: fix anon-only reclaim evicting file pages when swappiness=max
Date: Fri, 17 Jul 2026 09:37:29 -0700 [thread overview]
Message-ID: <alpaJU7_NMgz5ie4@linux.dev> (raw)
In-Reply-To: <20260717113300.214717-2-ridong.chen@linux.dev>
On Fri, Jul 17, 2026 at 07:32:58PM +0800, Ridong wrote:
> From: Ridong Chen <chenridong@xiaomi.com>
>
> 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.
>
> [1] https://lore.kernel.org/cgroups/7ddf3eee-5fe2-45f7-8614-c8936a039e04@linux.dev/
>
> Fixes: 68a1436bde00 ("mm: add swappiness=max arg to memory.reclaim for only anon reclaim")
> Suggested-by: Qi Zheng <qi.zheng@linux.dev>
> Signed-off-by: Ridong Chen <chenridong@xiaomi.com>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
next parent reply other threads:[~2026-07-17 16:37 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20260717113300.214717-1-ridong.chen@linux.dev>
[not found] ` <20260717113300.214717-2-ridong.chen@linux.dev>
2026-07-17 16:37 ` Shakeel Butt [this message]
[not found] ` <20260717113300.214717-3-ridong.chen@linux.dev>
2026-07-17 16:38 ` [PATCH 2/3] mm: vmscan: propagate real error code from per-node proactive reclaim Shakeel Butt
[not found] ` <20260717113300.214717-4-ridong.chen@linux.dev>
2026-07-17 16:39 ` [PATCH 3/3] mm: vmscan: drop unused gfp_mask parameter from __node_reclaim() Shakeel Butt
2026-07-17 19:53 ` [PATCH 0/3] mm/vmscan: fix swappiness=max and clean up per-node proactive reclaim Andrew Morton
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