linux-kernel - Re: [RFC] simple_lmk: Introduce Simple Low Memory Killer for Android

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Message-ID: <20190311214651.GA882@sultan-box.localdomain>
Date:   Mon, 11 Mar 2019 14:46:51 -0700
From:   Sultan Alsawaf <sultan@...neltoast.com>
To:     Joel Fernandes <joel@...lfernandes.org>
Cc:     Suren Baghdasaryan <surenb@...gle.com>,
        Michal Hocko <mhocko@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arve Hjønnevåg <arve@...roid.com>,
        Todd Kjos <tkjos@...roid.com>,
        Martijn Coenen <maco@...roid.com>,
        Christian Brauner <christian@...uner.io>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>, devel@...verdev.osuosl.org,
        linux-mm <linux-mm@...ck.org>, Tim Murray <timmurray@...gle.com>
Subject: Re: [RFC] simple_lmk: Introduce Simple Low Memory Killer for Android

On Mon, Mar 11, 2019 at 05:11:25PM -0400, Joel Fernandes wrote:
> But the point is that a transient temporary memory spike should not be a
> signal to kill _any_ process.  The reaction to kill shouldn't be so
> spontaneous that unwanted tasks are killed because the system went into
> panic mode. It should be averaged out which I believe is what PSI does.

In my patch from the first email, I implemented the decision to kill a process
at the same time that the existing kernel OOM killer decides to kill a process.
If the kernel's OOM killer were susceptible to killing processes due to
transient memory spikes, then I think there would have been several complaints
about this behavior regardless of which userspace or architecture is in use.
I think the existing OOM killer has this done right.

The decision to kill a process occurs after the page allocator has tried _very_
hard to satisfy a page allocation via alternative means, such as utilizing
compaction, flushing file-backed pages to disk via kswapd, and direct reclaim.
Once all of those means have failed, it is quite reasonable to kill a process to
free memory. Trying to wait out the memory starvation at this point would be
futile.

Thanks,
Sultan