linux-kernel - Re: [PATCH v2] memcg: introduce non-blocking limit setting option

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Message-ID: <aAa58xJFJ3du6OlY@google.com>
Date: Mon, 21 Apr 2025 21:34:43 +0000
From: Roman Gushchin <roman.gushchin@...ux.dev>
To: Shakeel Butt <shakeel.butt@...ux.dev>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...nel.org>,
	Muchun Song <muchun.song@...ux.dev>,
	Yosry Ahmed <yosry.ahmed@...ux.dev>, Tejun Heo <tj@...nel.org>,
	Michal Koutný <mkoutny@...e.com>,
	Greg Thelen <gthelen@...gle.com>, linux-mm@...ck.org,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
	Meta kernel team <kernel-team@...a.com>
Subject: Re: [PATCH v2] memcg: introduce non-blocking limit setting option

On Sat, Apr 19, 2025 at 11:35:45AM -0700, Shakeel Butt wrote:
> Setting the max and high limits can trigger synchronous reclaim and/or
> oom-kill if the usage is higher than the given limit. This behavior is
> fine for newly created cgroups but it can cause issues for the node
> controller while setting limits for existing cgroups.
> 
> In our production multi-tenant and overcommitted environment, we are
> seeing priority inversion when the node controller dynamically adjusts
> the limits of running jobs of different priorities. Based on the system
> situation, the node controller may reduce the limits of lower priority
> jobs and increase the limits of higher priority jobs. However we are
> seeing node controller getting stuck for long period of time while
> reclaiming from lower priority jobs while setting their limits and also
> spends a lot of its own CPU.
> 
> One of the workaround we are trying is to fork a new process which sets
> the limit of the lower priority job along with setting an alarm to get
> itself killed if it get stuck in the reclaim for lower priority job.
> However we are finding it very unreliable and costly. Either we need a
> good enough time buffer for the alarm to be delivered after setting
> limit and potentialy spend a lot of CPU in the reclaim or be unreliable
> in setting the limit for much shorter but cheaper (less reclaim) alarms.
> 
> Let's introduce new limit setting option which does not trigger
> reclaim and/or oom-kill and let the processes in the target cgroup to
> trigger reclaim and/or throttling and/or oom-kill in their next charge
> request. This will make the node controller on multi-tenant
> overcommitted environment much more reliable.
> 
> Signed-off-by: Shakeel Butt <shakeel.butt@...ux.dev>
> ---
> Changes since v1:
> - Instead of new interfaces use O_NONBLOCK flag (Greg, Roman & Tejun)
> 
>  Documentation/admin-guide/cgroup-v2.rst | 14 ++++++++++++++
>  mm/memcontrol.c                         | 10 ++++++++--
>  2 files changed, 22 insertions(+), 2 deletions(-)

Acked-by: Roman Gushchin <roman.gushchin@...ux.dev>

Re stable backports: can you, please, share some details about the problem
users are facing? Which kernel are they using?

Thanks!