linux-kernel - Re: [PATCH v3 1/2] mm: introduce process

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Date:   Mon, 2 Aug 2021 13:08:32 -0700
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     Michal Hocko <mhocko@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Rientjes <rientjes@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Roman Gushchin <guro@...com>, Rik van Riel <riel@...riel.com>,
        Minchan Kim <minchan@...nel.org>,
        Christian Brauner <christian@...uner.io>,
        Christoph Hellwig <hch@...radead.org>,
        Oleg Nesterov <oleg@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        Jann Horn <jannh@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Florian Weimer <fweimer@...hat.com>,
        Jan Engelhardt <jengelh@...i.de>,
        Tim Murray <timmurray@...gle.com>,
        Linux API <linux-api@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kernel-team <kernel-team@...roid.com>
Subject: Re: [PATCH v3 1/2] mm: introduce process_mrelease system call

On Mon, Aug 2, 2021 at 1:05 PM Shakeel Butt <shakeelb@...gle.com> wrote:
>
> On Mon, Aug 2, 2021 at 12:54 PM Suren Baghdasaryan <surenb@...gle.com> wrote:
> >
> > On Mon, Jul 26, 2021 at 6:44 AM Shakeel Butt <shakeelb@...gle.com> wrote:
> > >
> > > On Mon, Jul 26, 2021 at 12:27 AM Michal Hocko <mhocko@...e.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/
> >
> > Hi Folks,
> > So far I don't think there was any request for further changes.
> > Anything else you would want me to address or are we in a good shape
> > wrt this feature?
> > If so, would people who had a chance to review this patchset be
> > willing to endorse it with their Reviewed-by or Acked-by?
>
> I think with Michal's suggestion to use a killable mmap lock, at least
> I am good with the patch.

Ah, yes. Thanks for pointing this out! I'll replace mmap_read_lock()
with mmap_read_lock_killable(). Will post an updated version later
today.