linux-kernel - Re: [RFC PATCH 1/8] memcg: Enable fine-grained control of over memory.high action

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Message-ID: <d55bc1b8-da20-0366-8a54-d7dc6e2cc21d@redhat.com>
Date:   Tue, 18 Aug 2020 15:12:22 -0400
From:   Waiman Long <longman@...hat.com>
To:     Chris Down <chris@...isdown.name>,
        Shakeel Butt <shakeelb@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Jonathan Corbet <corbet@....net>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        LKML <linux-kernel@...r.kernel.org>, linux-doc@...r.kernel.org,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Cgroups <cgroups@...r.kernel.org>, Linux MM <linux-mm@...ck.org>
Subject: Re: [RFC PATCH 1/8] memcg: Enable fine-grained control of over
 memory.high action

On 8/17/20 12:56 PM, Chris Down wrote:
> Shakeel Butt writes:
>>> Sometimes, memory reclaim may not be able to recover memory in a rate
>>> that can catch up to the physical memory allocation rate especially
>>> when rotating disks are used for swapping or writing dirty pages. In
>>> this case, the physical memory consumption will keep on increasing.
>>
>> Isn't this the real underlying issue? Why not make the guarantees of
>> memory.high more strict instead of adding more interfaces and
>> complexity?
>
> Oh, thanks Shakeel for bringing this up. I missed this in the original 
> changelog and I'm surprised that it's mentioned, since we do have 
> protections against that.
>
> Waiman, we already added artificial throttling if memory reclaim is 
> not sufficiently achieved in 0e4b01df8659 ("mm, memcg: throttle 
> allocators when failing reclaim over memory.high"), which has been 
> present since v5.4. This should significantly inhibit physical memory 
> consumption from increasing. What problems are you having with that? :-)
>
Oh, I think I overlooked your patch. You are right. There are already 
throttling in place. So I need to re-examine my patch to see if it is 
still necessary or reduce the scope of the patch.

Thanks,
Longman