linux-kernel - Re: [patch 0/6] mm: memcg: statistics implementation cleanups

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Message-ID: <20120515110302.GH1406@cmpxchg.org>
Date:	Tue, 15 May 2012 13:03:02 +0200
From:	Johannes Weiner <hannes@...xchg.org>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...e.cz>, cgroups@...r.kernel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 0/6] mm: memcg: statistics implementation cleanups

On Tue, May 15, 2012 at 09:19:33AM +0900, KAMEZAWA Hiroyuki wrote:
> (2012/05/15 3:00), Johannes Weiner wrote:
> 
> > Before piling more things (reclaim stats) on top of the current mess,
> > I thought it'd be better to clean up a bit.
> > 
> > The biggest change is printing statistics directly from live counters,
> > it has always been annoying to declare a new counter in two separate
> > enums and corresponding name string arrays.  After this series we are
> > down to one of each.
> > 
> >  mm/memcontrol.c |  223 +++++++++++++++++------------------------------
> >  1 file changed, 82 insertions(+), 141 deletions(-)
> 
> to all 1-6. Thank you.
> 
> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>

Thanks!

> One excuse for my old implementation of mem_cgroup_get_total_stat(),
> which is fixed in patch 6, is that I thought it's better to touch all counters
> in a cachineline at once and avoiding long distance for-each loop.
> 
> What number of performance difference with some big hierarchy(100+children) tree ?
> (But I agree your code is cleaner. I'm just curious.)

I set up a parental group with hierarchy enabled, then created 512
children and did a 4-job kernel bench in one of them.  Every 0.1
seconds, I read the stats of the parent, which requires reading each
stat/event/lru item from 512 groups before moving to the next one:

                        512stats-vanilla        512stats-patched
Walltime (s)            62.61 (  +0.00%)        62.88 (  +0.43%)
Walltime (stddev)        0.17 (  +0.00%)         0.14 (  -3.17%)

That should be acceptable, I think.
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