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From:   Suren Baghdasaryan <surenb@google.com>
Date:   Tue, 12 Mar 2019 10:15:40 -0700
Message-ID: <CAJuCfpH9emgP=iaMy2_BEJ6HT3vvrvoeqTrCUXeBBD9VNR99kA@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>
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On Tue, Mar 12, 2019 at 9:58 AM Michal Hocko <mhocko@kernel.org> wrote:
>
> On Tue 12-03-19 09:37:41, Sultan Alsawaf wrote:
> > I have not had a chance to look at PSI yet, but
> > unless a PSI-enabled solution allows allocations to reach the same point as when
> > the OOM killer is invoked (which is contradictory to what it sets out to do),

LMK's job is to relieve memory pressure before we reach the boiling
point at which OOM killer has to be invoked. If we wait that long it
will definitely affect user experience. There might be usecases when
you might not care about this but on interactive systems like Android
it is important.

> > then it cannot take advantage of all of the alternative memory-reclaim means
> > employed in the slowpath, and will result in killing a process before it is
> > _really_ necessary.

I guess it's a matter of defining when is it _really_ necessary to
kill. In Android case that should be when the user starts suffering
from the delays caused by memory contention and that delay is exactly
what PSI is measuring.

> One more note. The above is true, but you can also hit one of the
> thrashing reclaim behaviors and reclaim last few pages again and again
> with the whole system really sluggish. That is what PSI is trying to
> help with.
> --
> Michal Hocko
> SUSE Labs