From: Daniel Colascione <dancol@google.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: Suren Baghdasaryan <surenb@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
Michal Hocko <mhocko@suse.com>,
David Rientjes <rientjes@google.com>,
yuzhoujian@didichuxing.com,
Souptick Joarder <jrdr.linux@gmail.com>,
Roman Gushchin <guro@fb.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
"Eric W. Biederman" <ebiederm@xmission.com>,
Shakeel Butt <shakeelb@google.com>,
Christian Brauner <christian@brauner.io>,
Minchan Kim <minchan@kernel.org>,
Tim Murray <timmurray@google.com>,
Joel Fernandes <joel@joelfernandes.org>,
Jann Horn <jannh@google.com>, linux-mm <linux-mm@kvack.org>,
lsf-pc@lists.linux-foundation.org,
LKML <linux-kernel@vger.kernel.org>,
kernel-team <kernel-team@android.com>
Subject: Re: [RFC 2/2] signal: extend pidfd_send_signal() to allow expedited process killing
Date: Thu, 11 Apr 2019 10:47:50 -0700 [thread overview]
Message-ID: <CAKOZuet8-en+tMYu_QqVCxmkak44T7MnmRgfJBot0+P_A+Qzkw@mail.gmail.com> (raw)
In-Reply-To: <20190411173649.GF22763@bombadil.infradead.org>
On Thu, Apr 11, 2019 at 10:36 AM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Thu, Apr 11, 2019 at 10:33:32AM -0700, Daniel Colascione wrote:
> > On Thu, Apr 11, 2019 at 10:09 AM Suren Baghdasaryan <surenb@google.com> wrote:
> > > On Thu, Apr 11, 2019 at 8:33 AM Matthew Wilcox <willy@infradead.org> wrote:
> > > >
> > > > On Wed, Apr 10, 2019 at 06:43:53PM -0700, Suren Baghdasaryan wrote:
> > > > > Add new SS_EXPEDITE flag to be used when sending SIGKILL via
> > > > > pidfd_send_signal() syscall to allow expedited memory reclaim of the
> > > > > victim process. The usage of this flag is currently limited to SIGKILL
> > > > > signal and only to privileged users.
> > > >
> > > > What is the downside of doing expedited memory reclaim? ie why not do it
> > > > every time a process is going to die?
> > >
> > > I think with an implementation that does not use/abuse oom-reaper
> > > thread this could be done for any kill. As I mentioned oom-reaper is a
> > > limited resource which has access to memory reserves and should not be
> > > abused in the way I do in this reference implementation.
> > > While there might be downsides that I don't know of, I'm not sure it's
> > > required to hurry every kill's memory reclaim. I think there are cases
> > > when resource deallocation is critical, for example when we kill to
> > > relieve resource shortage and there are kills when reclaim speed is
> > > not essential. It would be great if we can identify urgent cases
> > > without userspace hints, so I'm open to suggestions that do not
> > > involve additional flags.
> >
> > I was imagining a PI-ish approach where we'd reap in case an RT
> > process was waiting on the death of some other process. I'd still
> > prefer the API I proposed in the other message because it gets the
> > kernel out of the business of deciding what the right signal is. I'm a
> > huge believer in "mechanism, not policy".
>
> It's not a question of the kernel deciding what the right signal is.
> The kernel knows whether a signal is fatal to a particular process or not.
> The question is whether the killing process should do the work of reaping
> the dying process's resources sometimes, always or never. Currently,
> that is never (the process reaps its own resources); Suren is suggesting
> sometimes, and I'm asking "Why not always?"
FWIW, Suren's initial proposal is that the oom_reaper kthread do the
reaping, not the process sending the kill. Are you suggesting that
sending SIGKILL should spend a while in signal delivery reaping pages
before returning? I thought about just doing it this way, but I didn't
like the idea: it'd slow down mass-killing programs like killall(1).
Programs expect sending SIGKILL to be a fast operation that returns
immediately.
next prev parent reply other threads:[~2019-04-11 17:48 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-11 1:43 [RFC 0/2] opportunistic memory reclaim of a killed process Suren Baghdasaryan
2019-04-11 1:43 ` [RFC 1/2] mm: oom: expose expedite_reclaim to use oom_reaper outside of oom_kill.c Suren Baghdasaryan
2019-04-25 21:12 ` Tetsuo Handa
2019-04-25 21:56 ` Suren Baghdasaryan
2019-04-11 1:43 ` [RFC 2/2] signal: extend pidfd_send_signal() to allow expedited process killing Suren Baghdasaryan
2019-04-11 10:30 ` Christian Brauner
2019-04-11 10:34 ` Christian Brauner
2019-04-11 15:18 ` Suren Baghdasaryan
2019-04-11 15:23 ` Suren Baghdasaryan
2019-04-11 16:25 ` Daniel Colascione
2019-04-11 15:33 ` Matthew Wilcox
2019-04-11 17:05 ` Johannes Weiner
2019-04-11 17:09 ` Suren Baghdasaryan
2019-04-11 17:33 ` Daniel Colascione
2019-04-11 17:36 ` Matthew Wilcox
2019-04-11 17:47 ` Daniel Colascione [this message]
2019-04-12 6:49 ` Michal Hocko
2019-04-12 14:15 ` Suren Baghdasaryan
2019-04-12 14:20 ` Daniel Colascione
2019-04-12 21:03 ` Matthew Wilcox
2019-04-11 17:52 ` Suren Baghdasaryan
2019-04-11 21:45 ` Roman Gushchin
2019-04-11 21:59 ` Suren Baghdasaryan
2019-04-12 6:53 ` Michal Hocko
2019-04-12 14:10 ` Suren Baghdasaryan
2019-04-12 14:14 ` Daniel Colascione
2019-04-12 15:30 ` Daniel Colascione
2019-04-25 16:09 ` Suren Baghdasaryan
2019-04-11 10:51 ` [RFC 0/2] opportunistic memory reclaim of a killed process Michal Hocko
2019-04-11 16:18 ` Joel Fernandes
2019-04-11 18:12 ` Michal Hocko
2019-04-11 19:14 ` Joel Fernandes
2019-04-11 20:11 ` Michal Hocko
2019-04-11 21:11 ` Joel Fernandes
2019-04-11 16:20 ` Sandeep Patil
2019-04-11 16:47 ` Suren Baghdasaryan
2019-04-11 18:19 ` Michal Hocko
2019-04-11 19:56 ` Suren Baghdasaryan
2019-04-11 20:17 ` Michal Hocko
2019-04-11 17:19 ` Johannes Weiner
2019-04-11 11:51 ` [Lsf-pc] " Rik van Riel
2019-04-11 12:16 ` Michal Hocko
2019-04-11 16:54 ` Suren Baghdasaryan
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