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

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Message-ID: <20201020162714.GC46039@blackbook>
Date:   Tue, 20 Oct 2020 18:27:14 +0200
From:   Michal Koutný <mkoutny@...e.com>
To:     Roman Gushchin <guro@...com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        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

Hi.

On Mon, Oct 19, 2020 at 03:28:45PM -0700, Roman Gushchin <guro@...com> wrote:
> Currently the root memory cgroup is never charged directly, but
> if an ancestor cgroup is charged, the charge is propagated up to the
s/ancestor/descendant/

> The root memory cgroup doesn't show the charge to a user, neither it
> does allow to set any limits/protections.
An appealing claim, I'd like this to be true...

> Please, note, that cgroup v1 provides root level memory.usage_in_bytes.
> However, it's not based on page counters (refer to mem_cgroup_usage()).
...and it almost is. But there are still exposed kmem and tcpmem counters.


> To avoid multiple identical checks over the page counters
> code, for_each_nonroot_ancestor() macro is introduced.
If the assumptions behind this patch's idea were true, I think the
implementation would be simpler by merely (not)connecting the root
counters and keep the traversal as is.

> direct ascendants of the corresponding root memory cgroup's page
s/asc/desc/ ;-)

Michal

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