linux-kernel - Re: [PATCHv11 2/4] zbud: add to mm/

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Date:	Thu, 16 May 2013 11:30:34 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Seth Jennings <sjenning@...ux.vnet.ibm.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Nitin Gupta <ngupta@...are.org>,
	Minchan Kim <minchan@...nel.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Dan Magenheimer <dan.magenheimer@...cle.com>,
	Robert Jennings <rcj@...ux.vnet.ibm.com>,
	Jenifer Hopper <jhopper@...ibm.com>,
	Mel Gorman <mgorman@...e.de>,
	Johannes Weiner <jweiner@...hat.com>,
	Larry Woodman <lwoodman@...hat.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Dave Hansen <dave@...1.net>, Joe Perches <joe@...ches.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Cody P Schafer <cody@...ux.vnet.ibm.com>,
	Hugh Dickens <hughd@...gle.com>,
	Paul Mackerras <paulus@...ba.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, devel@...verdev.osuosl.org
Subject: Re: [PATCHv11 2/4] zbud: add to mm/

On 05/13/2013 08:40 AM, Seth Jennings wrote:
> zbud is an special purpose allocator for storing compressed pages. It is
> designed to store up to two compressed pages per physical page.  While this
> design limits storage density, it has simple and deterministic reclaim
> properties that make it preferable to a higher density approach when reclaim
> will be used.
>
> zbud works by storing compressed pages, or "zpages", together in pairs in a
> single memory page called a "zbud page".  The first buddy is "left
> justifed" at the beginning of the zbud page, and the last buddy is "right
> justified" at the end of the zbud page.  The benefit is that if either
> buddy is freed, the freed buddy space, coalesced with whatever slack space
> that existed between the buddies, results in the largest possible free region
> within the zbud page.
>
> zbud also provides an attractive lower bound on density. The ratio of zpages
> to zbud pages can not be less than 1.  This ensures that zbud can never "do
> harm" by using more pages to store zpages than the uncompressed zpages would
> have used on their own.
>
> This patch adds zbud to mm/ for later use by zswap.
>
> Signed-off-by: Seth Jennings <sjenning@...ux.vnet.ibm.com>

Acked-by: Rik van Riel <riel@...hat.com>


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