linux-kernel - Re: [patch] mm, memcg: avoid unnecessary function call when memcg is disabled

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Date:	Wed, 21 Nov 2012 10:02:34 +0900
From:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	David Rientjes <rientjes@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>, Hugh Dickins <hughd@...gle.com>,
	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [patch] mm, memcg: avoid unnecessary function call when memcg
 is disabled

(2012/11/21 6:49), Andrew Morton wrote:
> On Mon, 19 Nov 2012 17:44:34 -0800 (PST)
> David Rientjes <rientjes@...gle.com> wrote:
>
>> While profiling numa/core v16 with cgroup_disable=memory on the command
>> line, I noticed mem_cgroup_count_vm_event() still showed up as high as
>> 0.60% in perftop.
>>
>> This occurs because the function is called extremely often even when memcg
>> is disabled.
>>
>> To fix this, inline the check for mem_cgroup_disabled() so we avoid the
>> unnecessary function call if memcg is disabled.
>>
>> ...
>>
>> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
>> --- a/include/linux/memcontrol.h
>> +++ b/include/linux/memcontrol.h
>> @@ -181,7 +181,14 @@ unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
>>   						gfp_t gfp_mask,
>>   						unsigned long *total_scanned);
>>
>> -void mem_cgroup_count_vm_event(struct mm_struct *mm, enum vm_event_item idx);
>> +void __mem_cgroup_count_vm_event(struct mm_struct *mm, enum vm_event_item idx);
>> +static inline void mem_cgroup_count_vm_event(struct mm_struct *mm,
>> +					     enum vm_event_item idx)
>> +{
>> +	if (mem_cgroup_disabled() || !mm)
>> +		return;
>> +	__mem_cgroup_count_vm_event(mm, idx);
>> +}
>
> Does the !mm case occur frequently enough to justify inlining it, or
> should that test remain out-of-line?
>
I think this should be out-of-line.

Thanks,
-Kame

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