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

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Message-ID: <20190311175800.GA5522@sultan-box.localdomain>
Date:   Mon, 11 Mar 2019 10:58:00 -0700
From:   Sultan Alsawaf <sultan@...neltoast.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arve Hjønnevåg <arve@...roid.com>,
        Todd Kjos <tkjos@...roid.com>,
        Martijn Coenen <maco@...roid.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Christian Brauner <christian@...uner.io>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, devel@...verdev.osuosl.org,
        linux-mm@...ck.org, Suren Baghdasaryan <surenb@...gle.com>,
        Tim Murray <timmurray@...gle.com>
Subject: Re: [RFC] simple_lmk: Introduce Simple Low Memory Killer for Android

On Mon, Mar 11, 2019 at 06:43:20PM +0100, Michal Hocko wrote:
> I am sorry but we are not going to maintain two different OOM
> implementations in the kernel. From a quick look the implementation is
> quite a hack which is not really suitable for anything but a very
> specific usecase. E.g. reusing a freed page for a waiting allocation
> sounds like an interesting idea but it doesn't really work for many
> reasons. E.g. any NUMA affinity is broken, zone protection doesn't work
> either. Not to mention how the code hooks into the allocator hot paths.
> This is simply no no.
> 
> Last but not least people have worked really hard to provide means (PSI)
> to do what you need in the userspace.

Hi Michal,

Thanks for the feedback. I had no doubt that this would be vehemently rejected
on the mailing list, but I wanted feedback/opinions on it and thus sent it as anRFC. At best I thought perhaps the mechanisms I've employed might serve as
inspiration for LMKD improvements in Android, since this hacky OOM killer I've
devised does work quite well for the very specific usecase it is set out to
address. The NUMA affinity and zone protection bits are helpful insights too.

I'll take a look at PSI which Joel mentioned as well.

Thanks,
Sultan Alsawaf