linux-kernel - Re: [PATCH] mm: allow exiting processes to exceed the memory.max limit

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Message-ID: <c6cd075de18a277116a8908de6e0e4841a2dcae8.camel@surriel.com>
Date: Wed, 11 Dec 2024 11:28:19 -0500
From: Rik van Riel <riel@...riel.com>
To: Michal Hocko <mhocko@...e.com>
Cc: Johannes Weiner <hannes@...xchg.org>, kernel-team@...a.com, 
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, Roman Gushchin	
 <roman.gushchin@...ux.dev>, Shakeel Butt <shakeel.butt@...ux.dev>, Muchun
 Song	 <muchun.song@...ux.dev>, Andrew Morton <akpm@...ux-foundation.org>, 
	cgroups@...r.kernel.org
Subject: Re: [PATCH] mm: allow exiting processes to exceed the memory.max
 limit

On Mon, 2024-12-09 at 19:08 +0100, Michal Hocko wrote:
> On Mon 09-12-24 12:42:33, Rik van Riel wrote:
> > It is possible for programs to get stuck in exit, when their
> > memcg is at or above the memory.max limit, and things like
> > the do_futex() call from mm_release() need to page memory in.
> > 
> > This can hang forever, but it really doesn't have to.
> 
> Are you sure this is really happening?

The stuck is happening, albeit not stuck forever, but exit
taking hours before finally completing.

However, the fix may be to just allow the exiting task
to bypass "zswap no writeback" settings and write some
of the memory of its own cgroup to swap to get out of
the livelock:

https://lkml.org/lkml/2024/12/11/10102

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