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Date:   Tue, 18 Aug 2020 12:26:16 +0200
From:   peterz@infradead.org
To:     Chris Down <chris@chrisdown.name>
Cc:     Michal Hocko <mhocko@suse.com>, Waiman Long <longman@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Ingo Molnar <mingo@kernel.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, cgroups@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [RFC PATCH 0/8] memcg: Enable fine-grained per process memory
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On Tue, Aug 18, 2020 at 11:17:56AM +0100, Chris Down wrote:

> I'd ask that you understand a bit more about the tradeoffs and intentions of
> the patch before rushing in to declare its failure, considering it works
> just fine :-)
> 
> Clamping the maximal time allows the application to take some action to
> remediate the situation, while still being slowed down significantly. 2
> seconds per allocation batch is still absolutely plenty for any use case
> I've come across. If you have evidence it isn't, then present that instead
> of vague notions of "wrongness".

There is no feedback from the freeing rate, therefore it cannot be
correct in maintaining a maximum amount of pages.

0.5 pages / sec is still non-zero, and if the free rate is 0, you'll
crawl across whatever limit was set without any bounds. This is math
101.

It's true that I haven't been paying attention to mm in a while, but I
was one of the original authors of the I/O dirty balancing, I do think I
understand how these things work.