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From: Matthew Wilcox <willy@infradead.org>
To: Daniel Colascione <dancol@google.com>
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 10:36:49 -0700	[thread overview]
Message-ID: <20190411173649.GF22763@bombadil.infradead.org> (raw)
In-Reply-To: <CAKOZuetFU4tXE27bxA86zzDfNSCbw83p8fPxfkQ_d_Em0C04Sg@mail.gmail.com>

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?"

  reply	other threads:[~2019-04-11 17:37 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 [this message]
2019-04-11 17:47           ` Daniel Colascione
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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