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

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Message-ID: <20201130203425.GA1360286@carbon.DHCP.thefacebook.com>
Date:   Mon, 30 Nov 2020 12:34:25 -0800
From:   Roman Gushchin <guro@...com>
To:     Shakeel Butt <shakeelb@...gle.com>
CC:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/2] memcg: add pagetable comsumption to memory.stat

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?

Thanks!

> 
> Shakeel Butt (2):
>   mm: move lruvec stats update functions to vmstat.h
>   mm: memcontrol: account pagetables per node
> 
>  Documentation/admin-guide/cgroup-v2.rst |   3 +
>  arch/nds32/mm/mm-nds32.c                |   6 +-
>  drivers/base/node.c                     |   2 +-
>  fs/proc/meminfo.c                       |   2 +-
>  include/linux/memcontrol.h              | 112 ------------------------
>  include/linux/mm.h                      |  11 ++-
>  include/linux/mmzone.h                  |   2 +-
>  include/linux/vmstat.h                  | 104 ++++++++++++++++++++++
>  mm/memcontrol.c                         |  19 ++++
>  mm/page_alloc.c                         |   6 +-
>  10 files changed, 142 insertions(+), 125 deletions(-)
> 
> -- 
> 2.29.2.454.gaff20da3a2-goog
>