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Date:   Tue, 29 Jan 2019 15:43:06 +0100
From:   Michal Hocko <mhocko@kernel.org>
To:     Tejun Heo <tj@kernel.org>
Cc:     Johannes Weiner <hannes@cmpxchg.org>,
        Chris Down <chris@chrisdown.name>,
        Andrew Morton <akpm@linux-foundation.org>,
        Roman Gushchin <guro@fb.com>, Dennis Zhou <dennis@kernel.org>,
        linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
        linux-mm@kvack.org, kernel-team@fb.com
Subject: Re: [PATCH 2/2] mm: Consider subtrees in memory.events
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On Mon 28-01-19 09:49:05, Tejun Heo wrote:
> Hello, Michal.
> 
> On Mon, Jan 28, 2019 at 06:05:26PM +0100, Michal Hocko wrote:
> > Yeah, that is quite clear. But it also assumes that the hierarchy is
> > pretty stable but cgroups might go away at any time. I am not saying
> > that the aggregated events are not useful I am just saying that it is
> > quite non-trivial to use and catch all potential corner cases. Maybe I
> 
> It really isn't complicated and doesn't require stable subtree.
> 
> > am overcomplicating it but one thing is quite clear to me. The existing
> > semantic is really useful to watch for the reclaim behavior at the
> > current level of the tree. You really do not have to care what is
> > happening in the subtree when it is clear that the workload itself
> > is underprovisioned etc. Considering that such a semantic already
> > existis, somebody might depend on it and we likely want also aggregated
> > semantic then I really do not see why to risk regressions rather than
> > add a new memory.hierarchy_events and have both.
> 
> The problem then is that most other things are hierarchical including
> some fields in .events files, so if we try to add local stats and
> events, there's no good way to add them.

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?
-- 
Michal Hocko
SUSE Labs