linux-kernel - Re: [PATCH 1/4] numa: introduce per-cgroup numa balancing locality, statistic

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Message-ID: <20190712075815.GN3402@hirez.programming.kicks-ass.net>
Date:   Fri, 12 Jul 2019 09:58:15 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     王贇 <yun.wang@...ux.alibaba.com>
Cc:     hannes@...xchg.org, mhocko@...nel.org, vdavydov.dev@...il.com,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, mcgrof@...nel.org, keescook@...omium.org,
        linux-fsdevel@...r.kernel.org, cgroups@...r.kernel.org,
        Mel Gorman <mgorman@...e.de>, riel@...riel.com
Subject: Re: [PATCH 1/4] numa: introduce per-cgroup numa balancing locality,
 statistic

On Fri, Jul 12, 2019 at 11:43:17AM +0800, 王贇 wrote:
> 
> 
> On 2019/7/11 下午9:47, Peter Zijlstra wrote:
> [snip]
> >> +	rcu_read_lock();
> >> +	memcg = mem_cgroup_from_task(p);
> >> +	if (idx != -1)
> >> +		this_cpu_inc(memcg->stat_numa->locality[idx]);
> > 
> > I thought cgroups were supposed to be hierarchical. That is, if we have:
> > 
> >           R
> > 	 / \
> > 	 A
> > 	/\
> > 	  B
> > 	  \
> > 	   t1
> > 
> > Then our task t1 should be accounted to B (as you do), but also to A and
> > R.
> 
> I get the point but not quite sure about this...
> 
> Not like pages there are no hierarchical limitation on locality, also tasks

You can use cpusets to affect that.

> running in a particular group have no influence to others, not to mention the
> extra overhead, does it really meaningful to account the stuff hierarchically?

AFAIU it's a requirement of cgroups to be hierarchical. All our other
cgroup accounting is like that.