linux-kernel - Re: [PATCH] memcg: make mem_cgroup_read

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Message-ID: <20150925152017.GO16497@dhcp22.suse.cz>
Date:	Fri, 25 Sep 2015 17:20:17 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	Greg Thelen <gthelen@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Cgroups <cgroups@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] memcg: make mem_cgroup_read_stat() unsigned

On Wed 23-09-15 00:21:33, Greg Thelen wrote:
> 
> Andrew Morton wrote:
> 
> > On Tue, 22 Sep 2015 17:42:13 -0700 Greg Thelen <gthelen@...gle.com> wrote:
[...]
> >> I assume it's pretty straightforward to create generic
> >> percpu_counter_array routines which memcg could use.  Possibly something
> >> like this could be made general enough could be created to satisfy
> >> vmstat, but less clear.
> >> 
> >> [1] http://www.spinics.net/lists/cgroups/msg06216.html
> >> [2] https://lkml.org/lkml/2014/9/11/1057
> >
> > That all sounds rather bogus to me.  __percpu_counter_add() doesn't
> > modify struct percpu_counter at all except for when the cpu-local
> > counter overflows the configured batch size.  And for the memcg
> > application I suspect we can set the batch size to INT_MAX...
> 
> Nod.  The memory usage will be a bit larger, but the code reuse is
> attractive.  I dusted off Vladimir's
> https://lkml.org/lkml/2014/9/11/710.  Next step is to benchmark it
> before posting.

I am definitely in favor of using generic per-cpu counters.

-- 
Michal Hocko
SUSE Labs
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