linux-kernel - Re: [PATCH] mm/memcg: add unlikely to mercg->move_charge_at

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Date:	Tue, 19 Jun 2012 09:02:01 +0900
From:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Wanpeng Li <liwp.linux@...il.com>
CC:	Glauber Costa <glommer@...allels.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	Balbir Singh <bsingharora@...il.com>, cgroups@...r.kernel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Gavin Shan <shangw@...ux.vnet.ibm.com>
Subject: Re: [PATCH] mm/memcg: add unlikely to mercg->move_charge_at_immigrate

(2012/06/18 22:19), Wanpeng Li wrote:
> On Mon, Jun 18, 2012 at 05:09:36PM +0400, Glauber Costa wrote:
>> On 06/18/2012 05:10 PM, Wanpeng Li wrote:
>>> From: Wanpeng Li<liwp@...ux.vnet.ibm.com>
>>>
>>> move_charge_at_immigrate feature is disabled by default. Charges
>>> are moved only when you move mm->owner and it also add additional
>>> overhead.
>>
>> How big is this overhead?
>>
>> That's hardly a fast path. And if it happens to matter, it will be
>> just bigger when you enable it, and the compiler start giving the
>> wrong hints to the code.
>
> Thank you for your quick response.
>
> Oh, Maybe I should just write comments "move_charge_at_immigrate feature
> is disabled by default. So add "unlikely", in order to compiler can optimize."
>

This doesn't affect the performance. likely/unlikely which doesn't affect
performance is never welcomed.

Thanks,
-Kame

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