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

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Message-ID: <20190130193026.GA21410@cmpxchg.org>
Date:   Wed, 30 Jan 2019 14:30:26 -0500
From:   Johannes Weiner <hannes@...xchg.org>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     Tejun Heo <tj@...nel.org>, Michal Hocko <mhocko@...nel.org>,
        Chris Down <chris@...isdown.name>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <guro@...com>, Dennis Zhou <dennis@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Cgroups <cgroups@...r.kernel.org>, Linux MM <linux-mm@...ck.org>,
        kernel-team@...com
Subject: Re: [PATCH 2/2] mm: Consider subtrees in memory.events

On Wed, Jan 30, 2019 at 02:27:12PM -0500, Johannes Weiner wrote:
> On Wed, Jan 30, 2019 at 11:11:44AM -0800, Shakeel Butt wrote:
> > Hi Tejun,
> > 
> > On Wed, Jan 30, 2019 at 9:07 AM Tejun Heo <tj@...nel.org> wrote:
> > >
> > > Hello, Michal.
> > >
> > > On Wed, Jan 30, 2019 at 05:50:58PM +0100, Michal Hocko wrote:
> > > > > 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.
> > >
> > > Because the overall cost of shitty interface will be way higher in the
> > > longer term.  cgroup2 interface is far from perfect but is way better
> > > than cgroup1 especially for the memory controller.  Why do you think
> > > that is?
> > >
> > 
> > I thought you are fine with the separate interface for the hierarchical events.
> 
> Every other file in cgroup2 is hierarchical, but for recursive
> memory.events you'd need to read memory.events_tree?
> 
> Do we hate our users that much? :(

FTR, I would be okay with adding .local versions to existing files
where such a behavior could be useful. But that seems to be a separate
discussion from fixing memory.events here.