linux-kernel - Re: [PATCH] memcg: hugetlbfs basic usage accounting

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Message-ID: <20171115121508.GA2501@cmpxchg.org>
Date:   Wed, 15 Nov 2017 07:15:08 -0500
From:   Johannes Weiner <hannes@...xchg.org>
To:     Roman Gushchin <guro@...com>
Cc:     linux-mm@...ck.org, Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Tejun Heo <tj@...nel.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Dave Hansen <dave.hansen@...el.com>, kernel-team@...com,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] memcg: hugetlbfs basic usage accounting

On Tue, Nov 14, 2017 at 05:24:29PM +0000, Roman Gushchin wrote:
> This patch implements basic accounting of memory consumption
> by hugetlbfs pages for cgroup v2 memory controller.
> 
> Cgroup v2 memory controller lacks any visibility into the
> hugetlbfs memory consumption. Cgroup v1 implemented a separate
> hugetlbfs controller, which provided such stats, and also
> provided some control abilities. Although porting of the
> hugetlbfs controller to cgroup v2 is arguable a good idea and
> is outside of scope of this patch, it's very useful to have
> basic stats provided by memory.stat.
> 
> As hugetlbfs memory can easily represent a big portion of total
> memory, it's important to understand who (which memcg/container)
> is using it.

I'm not really buying this argument.

Hugetlb setups tend to be static configurations that require intimate
coordination between booting the kernel with a hugetlb reservation and
precisely setting up the application(s).

In the few cases where you need introspection, you can check the the
HugetlbPages entry in /proc/<pid>/status. The minor convenience
provided by adding an aggregate cgroup counter IMO doesn't outweigh
the weirdness of listing a type of resource in memory.stat that isn't
otherwise acknowledged or controllable as memory.