linux-kernel - Re: [PATCH 3/4] mm: zswap: add supporting for zsmalloc

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Date:	Tue, 20 Aug 2013 09:11:43 +0800
From:	Bob Liu <bob.liu@...cle.com>
To:	Seth Jennings <sjenning@...ux.vnet.ibm.com>
CC:	Bob Liu <lliubbo@...il.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, eternaleye@...il.com,
	minchan@...nel.org, mgorman@...e.de, gregkh@...uxfoundation.org,
	akpm@...ux-foundation.org, axboe@...nel.dk, ngupta@...are.org,
	semenzato@...gle.com, penberg@....fi, sonnyrao@...gle.com,
	smbarber@...gle.com, konrad.wilk@...cle.com, riel@...hat.com,
	kmpark@...radead.org
Subject: Re: [PATCH 3/4] mm: zswap: add supporting for zsmalloc


On 08/20/2013 12:59 AM, Seth Jennings wrote:
> On Sun, Aug 18, 2013 at 04:40:48PM +0800, Bob Liu wrote:
>> Make zswap can use zsmalloc as its allocater.
>> But note that zsmalloc don't reclaim any zswap pool pages mandatory, if zswap
>> pool gets full, frontswap_store will be refused unless frontswap_get happened
>> and freed some space.
>>
>> The reason of don't implement reclaiming zsmalloc pages from zswap pool is there
>> is no requiremnet currently.
>> If we want to do mandatory reclaim, we have to write those pages to real backend
>> swap devices. But most of current users of zsmalloc are from embeded world,
>> there is even no real backend swap device.
>> This action is also the same as privous zram!
>>
>> For several area, zsmalloc has unpredictable performance characteristics when
>> reclaiming a single page, then CONFIG_ZBUD are suggested.
> 
> Looking at this patch on its own, it does show how simple it could be
> for zswap to support zsmalloc.  So thanks!
> 
> However, I don't like all the ifdefs scattered everywhere.  I'd like to
> have a ops structure (e.g. struct zswap_alloc_ops) instead and just
> switch ops based on the CONFIG flag.  Or better yet, have it boot-time
> selectable instead of build-time.
> 

I don't like the ifdefs neither. But I didn't find a better way to
replace them since the data structures and API of zbud and zsmalloc are
different. I can take a try using zswap_alloc_ops.

-- 
Regards,
-Bob
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