linux-kernel - Re: [PATCH v2] mm/zswap: change zswap to writethrough cache

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Date:	Thu, 21 Nov 2013 08:42:53 +0800
From:	Bob Liu <bob.liu@...cle.com>
To:	Dan Streetman <ddstreet@...e.org>
CC:	Seth Jennings <sjennings@...iantweb.net>, linux-mm@...ck.org,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Minchan Kim <minchan@...nel.org>,
	Weijie Yang <weijie.yang@...sung.com>
Subject: Re: [PATCH v2] mm/zswap: change zswap to writethrough cache

Hi Dan,

On 11/21/2013 03:49 AM, Dan Streetman wrote:
> Currently, zswap is writeback cache; stored pages are not sent
> to swap disk, and when zswap wants to evict old pages it must
> first write them back to swap cache/disk manually.  This avoids
> swap out disk I/O up front, but only moves that disk I/O to
> the writeback case (for pages that are evicted), and adds the
> overhead of having to uncompress the evicted pages, and adds the
> need for an additional free page (to store the uncompressed page)
> at a time of likely high memory pressure.  Additionally, being
> writeback adds complexity to zswap by having to perform the
> writeback on page eviction.
> 

Good work!

> This changes zswap to writethrough cache by enabling
> frontswap_writethrough() before registering, so that any
> successful page store will also be written to swap disk.  All the
> writeback code is removed since it is no longer needed, and the
> only operation during a page eviction is now to remove the entry
> from the tree and free it.
> 

Could you do some testing using eg. SPECjbb? And compare the result with
original zswap.

Thanks,
-Bob
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