linux-kernel - Re: [PATCH v1] mm/vmscan: Add retry logic for cgroups with memory.low in kswapd

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Message-ID: <aPE84XfToVH4eAbs@tiehlicka>
Date: Thu, 16 Oct 2025 20:43:45 +0200
From: Michal Hocko <mhocko@...e.com>
To: Jiayuan Chen <jiayuan.chen@...ux.dev>
Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	Axel Rasmussen <axelrasmussen@...gle.com>,
	Yuanchu Xie <yuanchu@...gle.com>, Wei Xu <weixugc@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>,
	David Hildenbrand <david@...hat.com>,
	Qi Zheng <zhengqi.arch@...edance.com>,
	Shakeel Butt <shakeel.butt@...ux.dev>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] mm/vmscan: Add retry logic for cgroups with
 memory.low in kswapd

On Thu 16-10-25 15:10:31, Jiayuan Chen wrote:
[...]
> The issue we encountered is that since the watermark_boost parameter is enabled by
> default, it causes kswapd to be woken up even when memory watermarks are still relatively
> high. Due to rapid consecutive wake-ups, kswapd_failures eventually reaches MAX_RECLAIM_RETRIES,
> causing kswapd to stop running, which ultimately triggers direct memory reclaim.
>
> I believe we should choose another approach that avoids breaking the memory.low semantics.
> Specifically, in cases where kswapd is woken up due to watermark_boost, we should bypass the
> logic that increments kswapd_failures.

yes, this seems like unintended side effect of the implementation. Seems
like a rare problem as low limits would have to be configured very close
to kswapd watermarks. My assumption has always been that low limits are
not getting very close to watermarks because that makes any reclaim very
hard and configuration rather unstable but you might have a very good
reason to configure the memory protection that way. It would definitely
help to describe your specific setup with rationale so that we can look
into that closer.
-- 
Michal Hocko
SUSE Labs