Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20210723011436.60960-1-surenb@google.com> <CALvZod7ehaHoWRD-Pzvet5c1LQ6DYDHjs=xbJWZYEdMsgTpRgA@mail.gmail.com>
 <CAJuCfpFZeQez77CB7odfaSpi3JcLQ_Nz0WvDTsra1VPoA-j7sg@mail.gmail.com>
 <YPpfo2z8feq0vTlE@dhcp22.suse.cz> <CAJuCfpGSZwVgZ=FxhCV-uC_mzC7O-v-3k3tm-F6kOB7WM9t9tw@mail.gmail.com>
 <YPqDnqULylkkzQG5@dhcp22.suse.cz> <CALvZod4=9aEd9tUdku293uhVQ4mqsfYckCOKzqxXVTDYsmaVtQ@mail.gmail.com>
 <CAJuCfpGmpwTv92joNuVPaEJg1PigtGQn2daywHaqF4TXjuiCWQ@mail.gmail.com>
 <CALvZod7Vb2MKgCcSYtsMd8F4sFb2K7jQk3AGSECYfKvd3MNqzQ@mail.gmail.com> <YP5jyLeYsN3JtdX8@dhcp22.suse.cz>
In-Reply-To: <YP5jyLeYsN3JtdX8@dhcp22.suse.cz>
From:   Shakeel Butt <shakeelb@google.com>
Date:   Mon, 26 Jul 2021 06:43:50 -0700
Message-ID: <CALvZod4M6mF3VvAdade3n5fE1E0LQp+CeJHWLc+pHmZqqAhepg@mail.gmail.com>
Subject: Re: [PATCH v3 1/2] mm: introduce process_mrelease system call
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>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

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/