linux-kernel - Re: [PATCH] mm/zswap: add writethrough option

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Date:	Mon, 13 Jan 2014 12:03:05 -0500
From:	Dan Streetman <ddstreet@...e.org>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Seth Jennings <sjennings@...iantweb.net>
Cc:	Linux-MM <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Bob Liu <bob.liu@...cle.com>, Minchan Kim <minchan@...nel.org>,
	Weijie Yang <weijie.yang@...sung.com>,
	Shirish Pargaonkar <spargaonkar@...e.com>,
	Mel Gorman <mgorman@...e.de>
Subject: Re: [PATCH] mm/zswap: add writethrough option

Ping to see if this patch can get picked up.

On Fri, Jan 3, 2014 at 10:11 AM, Seth Jennings <sjennings@...iantweb.net> wrote:
> On Thu, Dec 19, 2013 at 08:23:27AM -0500, 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 the
>> need for an additional free page (to store the uncompressed page).
>>
>> This optionally changes zswap to writethrough cache by enabling
>> frontswap_writethrough() before registering, so that any
>> successful page store will also be written to swap disk.  The
>> default remains writeback.  To enable writethrough, the param
>> zswap.writethrough=1 must be used at boot.
>>
>> Whether writeback or writethrough will provide better performance
>> depends on many factors including disk I/O speed/throughput,
>> CPU speed(s), system load, etc.  In most cases it is likely
>> that writeback has better performance than writethrough before
>> zswap is full, but after zswap fills up writethrough has
>> better performance than writeback.
>>
>> Signed-off-by: Dan Streetman <ddstreet@...e.org>
>
> Hey Dan, sorry for the delay on this.  Vacation and busyness.
>
> This looks like a good option for those that don't mind having
> the write overhead to ensure that things don't really bog down
> if the compress pool overflows, while maintaining the read fault
> speedup by decompressing from the pool.
>
> Acked-by: Seth Jennings <sjennings@...iantweb.net>
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