linux-kernel - Re: [PATCH RFC 1/2] Add polling support to pidfd

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Message-ID: <20190411202006.GA130334@google.com>
Date:   Thu, 11 Apr 2019 16:20:06 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Christian Brauner <christian@...uner.io>
Cc:     linux-kernel@...r.kernel.org, luto@...capital.net,
        rostedt@...dmis.org, dancol@...gle.com, jannh@...gle.com,
        surenb@...gle.com, torvalds@...ux-foundation.org,
        Alexey Dobriyan <adobriyan@...il.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Andrei Vagin <avagin@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Kees Cook <keescook@...omium.org>,
        linux-fsdevel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        Michal Hocko <mhocko@...e.com>, Nadav Amit <namit@...are.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Serge Hallyn <serge@...lyn.com>, Shuah Khan <shuah@...nel.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Taehee Yoo <ap420073@...il.com>, Tejun Heo <tj@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>, kernel-team@...roid.com,
        Tycho Andersen <tycho@...ho.ws>
Subject: Re: [PATCH RFC 1/2] Add polling support to pidfd

On Thu, Apr 11, 2019 at 10:02:32PM +0200, Christian Brauner wrote:
> On April 11, 2019 10:00:59 PM GMT+02:00, Joel Fernandes <joel@...lfernandes.org> wrote:
> >On Thu, Apr 11, 2019 at 01:50:42PM -0400, Joel Fernandes (Google)
> >wrote:
> >> pidfd are /proc/pid directory file descriptors referring to a task
> >group
> >> leader. Android low memory killer (LMK) needs pidfd polling support
> >to
> >> replace code that currently checks for existence of /proc/pid for
> >> knowing a process that is signalled to be killed has died, which is
> >both
> >> racy and slow. The pidfd poll approach is race-free, and also allows
> >the
> >> LMK to do other things (such as by polling on other fds) while
> >awaiting
> >> the process being killed to die.
> >
> >It appears to me that the "pidfd" now will be an anon inode fd, and not
> >based
> >on /proc/, based on discussions with Linus. So I'll rework the patches
> >accordingly. However that is relatively independent of this patch so
> >this
> >version can also be reviewed before I send out the reworked version.
> 
> Thank you very much, Joel.
> I'm off this week and traveling but I'll try to give it a look asap.
> 
> Christian

Sounds great to me, thanks a lot Christian.

 - Joel