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

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Message-ID: <b027f9cc-edd2-840c-3829-176a1e298446@linux.alibaba.com>
Date:   Fri, 12 Jul 2019 11:43:17 +0800
From:   王贇 <yun.wang@...ux.alibaba.com>
To:     Peter Zijlstra <peterz@...radead.org>
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 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
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?

Regards,
Michael Wang

> 
>> +	rcu_read_unlock();
>> +}
>> +#endif