From: Johannes Weiner <hannes@cmpxchg.org>
To: Ridong Chen <ridong.chen@linux.dev>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Michal Hocko <mhocko@kernel.org>,
Roman Gushchin <roman.gushchin@linux.dev>,
Shakeel Butt <shakeel.butt@linux.dev>,
Muchun Song <muchun.song@linux.dev>, Chris Li <chrisl@kernel.org>,
Kairui Song <kasong@tencent.com>,
David Hildenbrand <david@kernel.org>,
Barry Song <baohua@kernel.org>, Yuanchu Xie <yuanchu@google.com>,
linux-mm@kvack.org, cgroups@vger.kernel.org,
linux-kernel@vger.kernel.org, Ridong Chen <chenridong@xiaomi.com>
Subject: Re: [PATCH 2/2] mm: vmscan: fix node reclaim ignoring swappiness parameter
Date: Mon, 13 Jul 2026 07:28:03 -0400 [thread overview]
Message-ID: <20260713112803.GF276793@cmpxchg.org> (raw)
In-Reply-To: <20260711091157.306070-3-ridong.chen@linux.dev>
On Sat, Jul 11, 2026 at 05:11:57PM +0800, Ridong Chen wrote:
> From: Ridong Chen <chenridong@xiaomi.com>
>
> sc_swappiness() had two separate definitions depending on
> CONFIG_MEMCG. The !CONFIG_MEMCG variant simply returned
> vm_swappiness, ignoring the proactive_swappiness value passed
> through scan_control. This caused the swappiness parameter
> written to /sys/devices/system/node/nodeX/reclaim to have no
> effect when CONFIG_MEMCG is disabled.
>
> Fix this by consolidating sc_swappiness() into a single definition
> that checks sc->proactive_swappiness first, then falls back to
> mem_cgroup_swappiness() which already handles both CONFIG_MEMCG
> and !CONFIG_MEMCG.
>
> Before fix (swappiness=max ignored, mostly file pages reclaimed):
>
> # cat /proc/sys/vm/swappiness
> 60
> # cat /proc/vmstat | grep pgsteal
> pgsteal_kswapd 0
> pgsteal_direct 0
> pgsteal_khugepaged 0
> pgsteal_proactive 1840
> pgsteal_anon 25
> pgsteal_file 1815
> # echo "64M swappiness=max" > /sys/devices/system/node/node0/reclaim
> # cat /proc/vmstat | grep pgsteal
> pgsteal_kswapd 0
> pgsteal_direct 0
> pgsteal_khugepaged 0
> pgsteal_proactive 18013
> pgsteal_anon 337
> pgsteal_file 17676
>
> After fix (swappiness=max honored, anon pages reclaimed as expected):
>
> # cat /proc/vmstat | grep pgsteal
> pgsteal_kswapd 0
> pgsteal_direct 0
> pgsteal_khugepaged 0
> pgsteal_proactive 0
> pgsteal_anon 0
> pgsteal_file 0
> # echo "64M swappiness=max" > /sys/devices/system/node/node0/reclaim
> # cat /proc/vmstat | grep pgsteal
> pgsteal_kswapd 0
> pgsteal_direct 0
> pgsteal_khugepaged 0
> pgsteal_proactive 16283
> pgsteal_anon 16283
> pgsteal_file 0
>
> Fixes: 68cd9050d871 ("mm: add swappiness= arg to memory.reclaim")
> Signed-off-by: Ridong Chen <chenridong@xiaomi.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
I would put Fixes: b980077899ea ("mm: introduce per-node proactive
reclaim interface") instead. It wasn't a bug before that.
Probably warrants a stable CC for 6.16 as well since this is pretty
user-visible breakage.
next prev parent reply other threads:[~2026-07-13 11:28 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-11 9:11 [PATCH 0/2] mm: fix node reclaim swappiness handling Ridong Chen
2026-07-11 9:11 ` [PATCH 1/2] memcg: move mem_cgroup_swappiness to memcontrol.h Ridong Chen
2026-07-13 15:08 ` Barry Song
2026-07-11 9:11 ` [PATCH 2/2] mm: vmscan: fix node reclaim ignoring swappiness parameter Ridong Chen
2026-07-13 11:28 ` Johannes Weiner [this message]
2026-07-13 15:16 ` Barry Song
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