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

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Message-ID: <20201016171502.GA102311@blackbook>
Date:   Fri, 16 Oct 2020 19:15:02 +0200
From:   Michal Koutný <mkoutny@...e.com>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Richard Palethorpe <rpalethorpe@...e.com>,
        Roman Gushchin <guro@...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
Subject: Re: [RFC PATCH] mm: memcg/slab: Stop reparented obj_cgroups from
 charging root

On Fri, Oct 16, 2020 at 10:53:08AM -0400, Johannes Weiner <hannes@...xchg.org> wrote:
> The central try_charge() function charges recursively all the way up
> to and including the root.
Except for use_hiearchy=0 (which is the case here as Richard
wrote). The reparenting is hence somewhat incompatible with
new_parent.use_hiearchy=0 :-/

> We should clean this up one way or another: either charge the root or
> don't, but do it consistently.
I agree this'd be good to unify. One upside of excluding root memcg from
charging is that users are spared from the charging overhead when memcg
tree is not created.  (Actually, I thought that was the reason for this
exception.)

Michal

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