linux-kernel - Re: [PATCH] readahead:add blk_run_backing

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Date:	Wed, 20 May 2009 10:52:58 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Hisashi Hifumi <hifumi.hisashi@....ntt.co.jp>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>, Jens Axboe <jens.axboe@...cle.com>
Subject: Re: [PATCH] readahead:add blk_run_backing_dev

On Wed, May 20, 2009 at 09:43:18AM +0800, Hisashi Hifumi wrote:
> 
> At 10:07 09/05/20, KOSAKI Motohiro wrote:
> >(cc to Wu and linux-mm)
> >
> >> Hi.
> >> 
> >> I wrote a patch that adds blk_run_backing_dev on page_cache_async_readahead
> >> so readahead I/O is unpluged to improve throughput.
> >> 
> >> Following is the test result with dd.
> >> 
> >> #dd if=testdir/testfile of=/dev/null bs=16384
> >> 
> >> -2.6.30-rc6
> >> 1048576+0 records in
> >> 1048576+0 records out
> >> 17179869184 bytes (17 GB) copied, 224.182 seconds, 76.6 MB/s
> >> 
> >> -2.6.30-rc6-patched
> >> 1048576+0 records in
> >> 1048576+0 records out
> >> 17179869184 bytes (17 GB) copied, 206.465 seconds, 83.2 MB/s
> >> 
> >> Sequential read performance on a big file was improved.
> >> Please merge my patch.
> >
> >I guess the improvement depend on readahead window size.
> >Have you mesure random access workload?
> 
> I tried with iozone. But there was no difference.

It does not impact random IO because the patch only modified the
*async* readahead path, and random IO is obviously *sync* ones.
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