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

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Message-ID: <20201016172635.GB102311@blackbook>
Date:   Fri, 16 Oct 2020 19:26:35 +0200
From:   Michal Koutný <mkoutny@...e.com>
To:     Richard Palethorpe <rpalethorpe@...e.de>
Cc:     Roman Gushchin <guro@...com>, ltp@...ts.linux.it,
        Johannes Weiner <hannes@...xchg.org>,
        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
Subject: Re: [RFC PATCH] mm: memcg/slab: Stop reparented obj_cgroups from
 charging root

On Fri, Oct 16, 2020 at 04:05:21PM +0100, Richard Palethorpe <rpalethorpe@...e.de> wrote:
> I'm don't know if that could happen without reparenting. I suppose if
> use_hierarchy=1 then actually this patch will result in root being
> overcharged, so perhaps it should also check for use_hierarchy?
Right, you'd need to distinguish whether the uncharged objcg was
originally (not)charged in the root memcg or it was only reparented to
it. (I originally considered only the genuine root objcgs.)

In this light, homogenous charing to root memcg looks really simpler but
I wonder what other surprises it brings about.

Michal

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