linux-kernel - Re: [PATCH v3] mm: memcg/slab: Stop reparented obj

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Date:   Tue, 20 Oct 2020 19:24:02 +0200
From:   Michal Koutný <mkoutny@...e.com>
To:     Richard Palethorpe <rpalethorpe@...e.de>
Cc:     Shakeel Butt <shakeelb@...gle.com>, Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        LTP List <ltp@...ts.linux.it>, Roman Gushchin <guro@...com>,
        Johannes Weiner <hannes@...xchg.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Lameter <cl@...ux.com>,
        Michal Hocko <mhocko@...nel.org>, Tejun Heo <tj@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH v3] mm: memcg/slab: Stop reparented obj_cgroups from
 charging root

Hi.

On Tue, Oct 20, 2020 at 06:52:08AM +0100, Richard Palethorpe <rpalethorpe@...e.de> wrote:
> I don't think that is relevant as we get the memcg from objcg->memcg
> which is set during reparenting. I suppose however, we can determine if
> the objcg was reparented by inspecting memcg->objcg.
+1

> If we just check use_hierarchy then objects directly charged to the
> memcg where use_hierarchy=0 will not be uncharged. However, maybe it is
> better to check if it was reparented and if use_hierarchy=0.
I think (I had to make a table) the yielded condition would be:

if ((memcg->use_hierarchy && reparented) || (!mem_cgroup_is_root(memcg) && !reparented))
	 __memcg_kmem_uncharge(memcg, nr_pages);

(I admit it's not very readable.)


Michal

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