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

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Date:	Wed, 20 May 2009 10:43:18 +0900
From:	Hisashi Hifumi <hifumi.hisashi@....ntt.co.jp>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-mm <linux-mm@...ck.org>,
	Wu Fengguang <fengguang.wu@...el.com>
Subject: Re: [PATCH] readahead:add blk_run_backing_dev


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.

>
>> 
>> Thanks.
>> 
>> Signed-off-by: Hisashi Hifumi <hifumi.hisashi@....ntt.co.jp>
>> 
>> diff -Nrup linux-2.6.30-rc6.org/mm/readahead.c 
>linux-2.6.30-rc6.unplug/mm/readahead.c
>> --- linux-2.6.30-rc6.org/mm/readahead.c	2009-05-18 10:46:15.000000000 +0900
>> +++ linux-2.6.30-rc6.unplug/mm/readahead.c	2009-05-18 13:00:42.000000000 +0900
>> @@ -490,5 +490,7 @@ page_cache_async_readahead(struct addres
>>  
>>  	/* do read-ahead */
>>  	ondemand_readahead(mapping, ra, filp, true, offset, req_size);
>> +
>> +	blk_run_backing_dev(mapping->backing_dev_info, NULL);
>>  }
>>  EXPORT_SYMBOL_GPL(page_cache_async_readahead);
>> 
>> --
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