linux-kernel - Re: [PATCH 2/2] mm: Consider subtrees in memory.events

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Date:   Wed, 30 Jan 2019 17:50:58 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Tejun Heo <tj@...nel.org>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Chris Down <chris@...isdown.name>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <guro@...com>, Dennis Zhou <dennis@...nel.org>,
        linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        linux-mm@...ck.org, kernel-team@...com
Subject: Re: [PATCH 2/2] mm: Consider subtrees in memory.events

On Tue 29-01-19 06:52:40, Tejun Heo wrote:
> Hello,
> 
> On Tue, Jan 29, 2019 at 03:43:06PM +0100, Michal Hocko wrote:
> > All memcg events are represented non-hierarchical AFAICS
> > memcg_memory_event() simply accounts at the level when it happens. Or do
> > I miss something? Or are you talking about .events files for other
> > controllers?
> 
> Yeah, cgroup.events and .stat files as some of the local stats would
> be useful too, so if we don't flip memory.events we'll end up with sth
> like cgroup.events.local, memory.events.tree and memory.stats.local,
> which is gonna be hilarious.

Why cannot we simply have memory.events_tree and be done with it? Sure
the file names are not goin to be consistent which is a minus but that
ship has already sailed some time ago.

> If you aren't willing to change your mind, the only option seems to be
> introducing a mount option to gate the flip and additions of local
> files.  Most likely, userspace will enable the option by default
> everywhere, so the end result will be exactly the same but I guess
> it'll better address your concern.

How does the consumer of the API learns about the mount type?
-- 
Michal Hocko
SUSE Labs