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

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Message-ID: <20130819165948.GA5703@variantweb.net>
Date:	Mon, 19 Aug 2013 11:59:48 -0500
From:	Seth Jennings <sjenning@...ux.vnet.ibm.com>
To:	Bob Liu <lliubbo@...il.com>
Cc:	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,
	Bob Liu <bob.liu@...cle.com>
Subject: Re: [PATCH 3/4] mm: zswap: add supporting for zsmalloc

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.

Seth

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