linux-kernel - Re: [PATCH 0/2] memcg: add pagetable comsumption to memory.stat

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Message-ID: <CALvZod4qiFuiByjh0+fwRoVw_EYVzqADNsiThf42-zDiXyYvpg@mail.gmail.com>
Date:   Mon, 30 Nov 2020 13:01:18 -0800
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Roman Gushchin <guro@...com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/2] memcg: add pagetable comsumption to memory.stat

On Mon, Nov 30, 2020 at 12:34 PM Roman Gushchin <guro@...com> wrote:
>
> On Wed, Nov 25, 2020 at 04:56:01PM -0800, Shakeel Butt wrote:
> > Many workloads consumes significant amount of memory in pagetables. This
> > patch series exposes the pagetable comsumption for each memory cgroup.
>
> Hi Shakeel!
>
> The code looks good to me. However I'm not sure I understand what's the
> use case for the new statistics? Can you, please, elaborate a bit more here?
>
> From a very first glance, the size of pagetables should be _roughly_ equal
> to the size_of(pte)/PAGE_SIZE*(size of a cgroup) and should not exceed 1%
> of the cgroup size. So for all but very large cgroups the value will be
> in the noise of per-cpu counters. Perhaps I'm missing some important cases?
>

I think this is in general a good metric to have but one specific
use-case we have is the user space network driver which mmaps the
memory of the applications for zero copy data transfers. This driver
can consume a large amount of memory in page tables. So, this metric
becomes really useful here.

Shakeel