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

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Message-ID: <20120618131918.GA2600@kernel>
Date:	Mon, 18 Jun 2012 21:19:32 +0800
From:	Wanpeng Li <liwp.linux@...il.com>
To:	Glauber Costa <glommer@...allels.com>
Cc:	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	Balbir Singh <bsingharora@...il.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	cgroups@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Gavin Shan <shangw@...ux.vnet.ibm.com>,
	Wanpeng Li <liwp.linux@...il.com>
Subject: Re: [PATCH] mm/memcg: add unlikely to mercg->move_charge_at_immigrate

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."

Best Regards,
Wanpeng Li

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