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

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Date:   Tue, 3 Nov 2020 13:28:51 -0800
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     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>,
        Minchan Kim <minchan@...nel.org>,
        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 1:35 AM Michal Hocko <mhocko@...e.com> 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...

Hmm. Adding a new SIGKILL_SYNC seems to require quite a surgery...
That will cause a change to SIGRTMIN which is used by glib and also
would affect RTSIG_MAX which I think is also used by the userspace.
I'm not sure such a change would be acceptable...

IIUC, Minchan's alternative suggestion was to do mm reaping from
inside fsync() in cases like these:

pidfd_send_signal(pidfd, SIGKILL); // send SIGKILL as usual
fsync(pidfd); // causes mm reaping in the context of the caller

I can prototype this approach quite easily and quickly and post an RFC
to energize the discussion. Any objections?

> --
> Michal Hocko
> SUSE Labs