linux-kernel - Re: [PATCH] mm/memcontrol: add memory.peak in cgroup root

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Date:   Thu, 23 Feb 2023 14:00:06 -0800
From:   Roman Gushchin <roman.gushchin@...ux.dev>
To:     Matthew Chae <Matthew.Chae@...s.com>
Cc:     Michal Koutný <mkoutny@...e.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        kernel <kernel@...s.com>,
        Christopher Wong <Christopher.Wong@...s.com>,
        Muchun Song <muchun.song@...ux.dev>,
        "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm/memcontrol: add memory.peak in cgroup root

On Thu, Feb 23, 2023 at 07:00:57PM +0000, Matthew Chae wrote:
> Hi Roman,
> 
> I'd like to get the peak memory usage recorded overall time, rather than at a certain time.
> Plus, I expect that the systematical way might have better performance compared to userspace sampling.

I'm not necessarily saying to do this in userspace, you can try add a new system-wide counter
(new /proc/vmstat entry). Obviously, it might be easier to do this in userspace.
My point is to do it on system level rather than cgroup level and record a bottom of free
memory rather than the peak of used memory.

> If I understand correctly, recording the bottom of available free memory might not be helpful for this.
> Am I missing something?

Why?