Re: [PATCH v3 1/2] mm: introduce process_mrelease system call

From: Shakeel Butt <shakeelb@google.com>
To: Michal Hocko <mhocko@suse.com>
Cc: Suren Baghdasaryan <surenb@google.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	David Rientjes <rientjes@google.com>,
	Matthew Wilcox <willy@infradead.org>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Roman Gushchin <guro@fb.com>, Rik van Riel <riel@surriel.com>,
	Minchan Kim <minchan@kernel.org>,
	Christian Brauner <christian@brauner.io>,
	Christoph Hellwig <hch@infradead.org>,
	Oleg Nesterov <oleg@redhat.com>,
	David Hildenbrand <david@redhat.com>,
	Jann Horn <jannh@google.com>, Andy Lutomirski <luto@kernel.org>,
	Christian Brauner <christian.brauner@ubuntu.com>,
	Florian Weimer <fweimer@redhat.com>,
	Jan Engelhardt <jengelh@inai.de>,
	Tim Murray <timmurray@google.com>,
	Linux API <linux-api@vger.kernel.org>,
	Linux MM <linux-mm@kvack.org>,
	LKML <linux-kernel@vger.kernel.org>,
	kernel-team <kernel-team@android.com>
Subject: Re: [PATCH v3 1/2] mm: introduce process_mrelease system call
Date: Mon, 26 Jul 2021 06:43:50 -0700	[thread overview]
Message-ID: <CALvZod4M6mF3VvAdade3n5fE1E0LQp+CeJHWLc+pHmZqqAhepg@mail.gmail.com> (raw)
In-Reply-To: <YP5jyLeYsN3JtdX8@dhcp22.suse.cz>

On Mon, Jul 26, 2021 at 12:27 AM Michal Hocko <mhocko@suse.com> wrote:
>
[...]
>
> Is process_mrelease on all of them really necessary? I thought that the
> primary reason for the call is to guarantee a forward progress in cases
> where the userspace OOM victim cannot die on SIGKILL. That should be
> more an exception than a normal case, no?
>

I am thinking of using this API in this way: On user-defined OOM
condition, kill a job/cgroup and unconditionally reap all of its
processes. Keep monitoring the situation and if it does not improve go
for another kill and reap.

I can add additional logic in between kill and reap to see if reap is
necessary but unconditionally reaping is more simple.

>
> > An alternative would be to have a cgroup specific interface for
> > reaping similar to cgroup.kill.
>
> Could you elaborate?
>

I mentioned this in [1] where I was thinking if it makes sense to
overload cgroup.kill to also add the SIGKILLed processes in
oom_reaper_list. The downside would be that there will be one thread
doing the reaping and the syscall approach allows userspace to reap in
multiple threads. I think for now, I would go with whatever Suren is
proposing and we can always add more stuff if need arises.

[1] https://lore.kernel.org/containers/CALvZod4jsb6bFzTOS4ZRAJGAzBru0oWanAhezToprjACfGm+ew@mail.gmail.com/