Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
References: <20190310203403.27915-1-sultan@kerneltoast.com>
 <20190311174320.GC5721@dhcp22.suse.cz> <20190311175800.GA5522@sultan-box.localdomain>
 <CAJuCfpHTjXejo+u--3MLZZj7kWQVbptyya4yp1GLE3hB=BBX7w@mail.gmail.com>
 <20190311204626.GA3119@sultan-box.localdomain> <CAJuCfpGpBxofTT-ANEEY+dFCSdwkQswox3s8Uk9Eq0BnK9i0iA@mail.gmail.com>
 <20190312080532.GE5721@dhcp22.suse.cz>
In-Reply-To: <20190312080532.GE5721@dhcp22.suse.cz>
From:   Suren Baghdasaryan <surenb@google.com>
Date:   Tue, 12 Mar 2019 07:36:58 -0700
Message-ID: <CAJuCfpFToMiU8pyjA5QDduG0V8-UZSq1EesstFRUC6_YvbDDQA@mail.gmail.com>
Subject: Re: [RFC] simple_lmk: Introduce Simple Low Memory Killer for Android
To:     Michal Hocko <mhocko@kernel.org>
Cc:     Sultan Alsawaf <sultan@kerneltoast.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        =?UTF-8?B?QXJ2ZSBIasO4bm5ldsOlZw==?= <arve@android.com>,
        Todd Kjos <tkjos@android.com>,
        Martijn Coenen <maco@android.com>,
        Joel Fernandes <joel@joelfernandes.org>,
        Christian Brauner <christian@brauner.io>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        LKML <linux-kernel@vger.kernel.org>, devel@driverdev.osuosl.org,
        linux-mm <linux-mm@kvack.org>, Tim Murray <timmurray@google.com>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue, Mar 12, 2019 at 1:05 AM Michal Hocko <mhocko@kernel.org> wrote:
>
> On Mon 11-03-19 15:15:35, Suren Baghdasaryan wrote:
> > On Mon, Mar 11, 2019 at 1:46 PM Sultan Alsawaf <sultan@kerneltoast.com> wrote:
> > >
> > > On Mon, Mar 11, 2019 at 01:10:36PM -0700, Suren Baghdasaryan wrote:
> > > > The idea seems interesting although I need to think about this a bit
> > > > more. Killing processes based on failed page allocation might backfire
> > > > during transient spikes in memory usage.
> > >
> > > This issue could be alleviated if tasks could be killed and have their pages
> > > reaped faster. Currently, Linux takes a _very_ long time to free a task's memory
> > > after an initial privileged SIGKILL is sent to a task, even with the task's
> > > priority being set to the highest possible (so unwanted scheduler preemption
> > > starving dying tasks of CPU time is not the issue at play here). I've
> > > frequently measured the difference in time between when a SIGKILL is sent for a
> > > task and when free_task() is called for that task to be hundreds of
> > > milliseconds, which is incredibly long. AFAIK, this is a problem that LMKD
> > > suffers from as well, and perhaps any OOM killer implementation in Linux, since
> > > you cannot evaluate effect you've had on memory pressure by killing a process
> > > for at least several tens of milliseconds.
> >
> > Yeah, killing speed is a well-known problem which we are considering
> > in LMKD. For example the recent LMKD change to assign process being
> > killed to a cpuset cgroup containing big cores cuts the kill time
> > considerably. This is not ideal and we are thinking about better ways
> > to expedite the cleanup process.
>
> If you design is relies on the speed of killing then it is fundamentally
> flawed AFAICT. You cannot assume anything about how quickly a task dies.
> It might be blocked in an uninterruptible sleep or performin an
> operation which takes some time. Sure, oom_reaper might help here but
> still.

That's what I was considering. This is not a silver bullet but
increased speed would not hurt.

> The only way to control the OOM behavior pro-actively is to throttle
> allocation speed. We have memcg high limit for that purpose. Along with
> PSI, I can imagine a reasonably working user space early oom
> notifications and reasonable acting upon that.

That makes sense and we are working in this direction.

> --
> Michal Hocko
> SUSE Labs

Thanks,
Suren.