linux-kernel - Re: [RFC]: userspace memory reaping

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Message-ID: <CAJuCfpELVYSNsjnXvg7pXQiwMBYpffcy5aNqj84t70-qN1XYiQ@mail.gmail.com>
Date:   Tue, 3 Nov 2020 13:40:41 -0800
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Michal Hocko <mhocko@...e.com>, linux-api@...r.kernel.org,
        linux-mm <linux-mm@...ck.org>,
        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>,
        Christian Brauner <christian@...uner.io>,
        Oleg Nesterov <oleg@...hat.com>,
        Tim Murray <timmurray@...gle.com>,
        kernel-team <kernel-team@...roid.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Mel Gorman <mgorman@...hsingularity.net>
Subject: Re: [RFC]: userspace memory reaping

On Tue, Nov 3, 2020 at 1:32 PM Minchan Kim <minchan@...nel.org> wrote:
>
> On Tue, Nov 03, 2020 at 10:35:50AM +0100, Michal Hocko wrote:
> > On Mon 02-11-20 12:29:24, Suren Baghdasaryan wrote:
> > [...]
> > > To follow up on this. Should I post an RFC implementing SIGKILL_SYNC
> > > which in addition to sending a kill signal would also reap the
> > > victim's mm in the context of the caller? Maybe having some code will
> > > get the discussion moving forward?
> >
> > Yeah, having a code, even preliminary, might help here. This definitely
> > needs a good to go from process management people as that proper is land
> > full of surprises...
>
> Just to remind a idea I suggested to reuse existing concept
>
>     fd = pidfd_open(victim process)
>     fdatasync(fd);
>     close(fd);
>

Yep, I just posted a comment about that. I think though your above
sequence is missing a pidfd_send_signal(fd, SIGKILL) before the
fdatasync(fd)...
Not sure if fdatasync(pidfd) or fsync(pidfd) would be more appropriate
for this but will use one and we can discuss details in the RFC with
the code.
Thanks!