linux-kernel - Re: [RFC PATCH] mm: memcg/slab: Stop reparented obj

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Message-ID: <20201020181822.GA397401@cmpxchg.org>
Date:   Tue, 20 Oct 2020 14:18:22 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Roman Gushchin <guro@...com>
Cc:     Michal Koutný <mkoutny@...e.com>,
        Richard Palethorpe <rpalethorpe@...e.com>, ltp@...ts.linux.it,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Christoph Lameter <cl@...ux.com>,
        Michal Hocko <mhocko@...nel.org>, Tejun Heo <tj@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Michal Hocko <mhocko@...e.com>
Subject: Re: [RFC PATCH] mm: memcg/slab: Stop reparented obj_cgroups from
 charging root

On Tue, Oct 20, 2020 at 10:07:17AM -0700, Roman Gushchin wrote:
> If we want these counter to function properly, then we should go into the opposite
> direction and remove the special handling of the root memory cgroup in many places.

I suspect this is also by far the most robust solution from a code and
maintenance POV.

I don't recall the page counter at the root level having been a
concern in recent years, even though it's widely used in production
environments. It's lockless and cache compact. It's also per-cpu
batched, which means it isn't actually part of the memcg hotpath.