linux-kernel - Re: [PATCH 2/2] huge-memory: Use fast mm counters for transparent huge pages

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Message-ID: <4F829575.4020704@jp.fujitsu.com>
Date:	Mon, 09 Apr 2012 16:53:25 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	linux-kernel@...r.kernel.org, tim.c.chen@...ux.intel.com,
	linux-mm@...ck.org, Andi Kleen <ak@...ux.intel.com>,
	aarcange@...hat.com
Subject: Re: [PATCH 2/2] huge-memory: Use fast mm counters for transparent
 huge pages

(2012/03/31 23:09), Andi Kleen wrote:

> From: Andi Kleen <ak@...ux.intel.com>
> 
> We found that the mm struct anon page counter cache line is much hotter
> with transparent huge pages compared to small pages.
> 
> Small pages use a special fast counter mechanism in task_struct, but huge pages
> didn't.  The huge pages are larger than the normal 64 entry threshold for the
> fast counter, so it cannot be directly used. Use a new special counter for huge
> pages to handle them efficiently.
> 
> Any users just calculate the correct total.
> 
> The only special case is transferring the large page count to small pages
> when splitting. I put it somewhat arbitarily into the tricky split
> sequence. Some review on this part is appreciated.
> 
> [An alternative would be to not do that, but that could lead to
> negative counters. These should still give the correct result]
> 
> Contains a fix for a problem found by Andrea in review.
> 
> Cc: aarcange@...hat.com
> Signed-off-by: Andi Kleen <ak@...ux.intel.com>


Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>


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