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Date:   Tue, 20 Oct 2020 14:18:22 -0400
From:   Johannes Weiner <hannes@cmpxchg.org>
To:     Roman Gushchin <guro@fb.com>
Cc:     Michal =?iso-8859-1?Q?Koutn=FD?= <mkoutny@suse.com>,
        Richard Palethorpe <rpalethorpe@suse.com>, ltp@lists.linux.it,
        Andrew Morton <akpm@linux-foundation.org>,
        Shakeel Butt <shakeelb@google.com>,
        Christoph Lameter <cl@linux.com>,
        Michal Hocko <mhocko@kernel.org>, Tejun Heo <tj@kernel.org>,
        Vlastimil Babka <vbabka@suse.cz>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Michal Hocko <mhocko@suse.com>
Subject: Re: [RFC PATCH] mm: memcg/slab: Stop reparented obj_cgroups from
 charging root
Message-ID: <20201020181822.GA397401@cmpxchg.org>
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 <20201016145308.GA312010@cmpxchg.org>
 <20201016171502.GA102311@blackbook>
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 <20201020162714.GC46039@blackbook>
 <20201020170717.GA153102@carbon.DHCP.thefacebook.com>
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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.