linux-kernel - Re: [PATCH] mm, memcg: Optionally disable memcg by default using Kconfig

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Date:	Tue, 19 May 2015 17:12:35 +0200
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Michal Hocko <mhocko@...e.cz>, Johannes Weiner <hannes@...xchg.org>
CC:	Mel Gorman <mgorman@...e.de>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>, cgroups@...r.kernel.org
Subject: Re: [PATCH] mm, memcg: Optionally disable memcg by default using
 Kconfig

On 05/19/2015 04:53 PM, Michal Hocko wrote:
> On Tue 19-05-15 10:18:07, Johannes Weiner wrote:
>> CC'ing Tejun and cgroups for the generic cgroup interface part
>>
>> On Tue, May 19, 2015 at 11:40:57AM +0100, Mel Gorman wrote:
> [...]
>>> /usr/src/linux-4.0-vanilla/mm/memcontrol.c                           6.6441   395842
>>>    mem_cgroup_try_charge                                                        2.950%   175781
>>
>> Ouch.  Do you have a way to get the per-instruction breakdown of this?
>> This function really isn't doing much.  I'll try to reproduce it here
>> too, I haven't seen such high costs with pft in the past.
>>
>>>    try_charge                                                                   0.150%     8928
>>>    get_mem_cgroup_from_mm                                                       0.121%     7184
>
> Indeed! try_charge + get_mem_cgroup_from_mm which I would expect to be
> the biggest consumers here are below 10% of the mem_cgroup_try_charge.

Note that they don't explain 10% of the mem_cgroup_try_charge. They 
*add* their own overhead to the overhead of mem_cgroup_try_charge 
itself. Which might be what you meant but I wasn't sure.

> Other than that the function doesn't do much else than some flags
> queries and css_put...
>
> Do you have the full trace?
> Sorry for a stupid question but do inlines
> from other header files get accounted to memcontrol.c?

Yes, perf doesn't know about them so it's accounted to function where 
the code physically is.

>
> [...]
>

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