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 <20240111192807.GA424308@cmpxchg.org>
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From: Shakeel Butt <shakeelb@google.com>
Date: Fri, 12 Jan 2024 11:04:06 -0800
Message-ID: <CALvZod6eb2uPPW+y=CnB_KumOW-MJjqJK=zOqfzwwJ-JX9eP0g@mail.gmail.com>
Subject: Re: [PATCH] mm: memcontrol: don't throttle dying tasks on memory.high
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>, Andrew Morton <akpm@linux-foundation.org>, 
	Michal Hocko <mhocko@kernel.org>, Muchun Song <muchun.song@linux.dev>, Tejun Heo <tj@kernel.org>, 
	Dan Schatzberg <schatzberg.dan@gmail.com>, cgroups@vger.kernel.org, linux-mm@kvack.org, 
	linux-kernel@vger.kernel.org
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On Thu, Jan 11, 2024 at 11:28=E2=80=AFAM Johannes Weiner <hannes@cmpxchg.or=
g> wrote:
>
[...]
>
> From 6124a13cb073f5ff06b9c1309505bc937d65d6e5 Mon Sep 17 00:00:00 2001
> From: Johannes Weiner <hannes@cmpxchg.org>
> Date: Thu, 11 Jan 2024 07:18:47 -0500
> Subject: [PATCH] mm: memcontrol: don't throttle dying tasks on memory.hig=
h
>
> While investigating hosts with high cgroup memory pressures, Tejun
> found culprit zombie tasks that had were holding on to a lot of
> memory, had SIGKILL pending, but were stuck in memory.high reclaim.
>
> In the past, we used to always force-charge allocations from tasks
> that were exiting in order to accelerate them dying and freeing up
> their rss. This changed for memory.max in a4ebf1b6ca1e ("memcg:
> prohibit unconditional exceeding the limit of dying tasks"); it noted
> that this can cause (userspace inducable) containment failures, so it
> added a mandatory reclaim and OOM kill cycle before forcing charges.
> At the time, memory.high enforcement was handled in the userspace
> return path, which isn't reached by dying tasks, and so memory.high
> was still never enforced by dying tasks.
>
> When c9afe31ec443 ("memcg: synchronously enforce memory.high for large
> overcharges") added synchronous reclaim for memory.high, it added
> unconditional memory.high enforcement for dying tasks as well. The
> callstack shows that this path is where the zombie is stuck in.
>
> We need to accelerate dying tasks getting past memory.high, but we
> cannot do it quite the same way as we do for memory.max: memory.max is
> enforced strictly, and tasks aren't allowed to move past it without
> FIRST reclaiming and OOM killing if necessary. This ensures very small
> levels of excess. With memory.high, though, enforcement happens lazily
> after the charge, and OOM killing is never triggered. A lot of
> concurrent threads could have pushed, or could actively be pushing,
> the cgroup into excess. The dying task will enter reclaim on every
> allocation attempt, with little hope of restoring balance.
>
> To fix this, skip synchronous memory.high enforcement on dying tasks
> altogether again. Update memory.high path documentation while at it.
>
> Fixes: c9afe31ec443 ("memcg: synchronously enforce memory.high for large =
overcharges")
> Reported-by: Tejun Heo <tj@kernel.org>
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

Acked-by: Shakeel Butt <shakeelb@google.com>

I am wondering if you have seen or suspected a similar issue but for
remote memcg charging. For example pageout on a global reclaim which
has to allocate buffers for some other memcg.