linux-kernel - Re: [PATCH] mm: Add unlikely for current

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Message-ID: <51BE6BFC.3030009@cn.fujitsu.com>
Date:	Mon, 17 Jun 2013 09:53:00 +0800
From:	Zhang Yanfei <zhangyanfei@...fujitsu.com>
To:	David Rientjes <rientjes@...gle.com>
CC:	Zhang Yanfei <zhangyanfei.yes@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux MM <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: Add unlikely for current_order test

Hi David,

On 06/17/2013 02:04 AM, David Rientjes wrote:
> On Sat, 15 Jun 2013, Zhang Yanfei wrote:
> 
>> From: Zhang Yanfei <zhangyanfei@...fujitsu.com>
>>
>> Since we have an unlikely for the "current_order >= pageblock_order / 2"
>> test above, adding an unlikely for this "current_order >= pageblock_order"
>> test seems more appropriate.
>>
> 
> I don't understand the justification at all, current_order being unlikely 
> greater than or equal to pageblock_order / 2 doesn't imply at all that 
> it's unlikely that current_order is greater than or equal to 
> pageblock_order.
> 

hmmm... I am confused. Since current_order is >= pageblock_order / 2 is unlikely,
why current_order is >= pageblock_order isn't unlikely. Or there are other
tips?

Actually, I am also a little confused about why current_order should be
unlikely greater than or equal to pageblock_order / 2. When borrowing pages
with other migrate_type, we always search from MAX_ORDER-1, which is greater
or equal to pageblock_order.

-- 
Thanks.
Zhang Yanfei
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