linux-kernel - Re: [PATCH] fs/direct-io.c: Calcuate fs_count correctly in get_more

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Date:	Tue, 20 Sep 2011 10:13:27 +0800
From:	Tao Ma <tm@....ma>
To:	Andrew Morton <akpm@...gle.com>
CC:	linux-kernel@...r.kernel.org, Theodore Ts'o <tytso@....edu>,
	Christoph Hellwig <hch@....de>,
	Al Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] fs/direct-io.c: Calcuate fs_count correctly in get_more_blocks.

On 09/20/2011 06:31 AM, Andrew Morton wrote:
> On Mon, 19 Sep 2011 16:25:39 +0800
> Tao Ma <tm@....ma> wrote:
> 
>> In get_more_blocks, we use dio_count to calcuate fs_count and do some
>> tricky things to increase fs_count if dio_count isn't aligned. But
>> actually it still has some cornor case that can't be coverd. See the
>> following example:
>> ./dio_write foo -s 1024 -w 4096(direct write 4096 bytes at offset 1024).
>> The same goes if the offset isn't aligned to fs_blocksize.
>>
>> In this case, the old calculation counts fs_count to be 1, but actually
>> we will write into 2 different blocks(if fs_blocksize=4096). The old code
>> just works, since it will call get_block twice(and may have to allocate
>> and create extent twice for file systems like ext4). So we'd better call
>> get_block just once with the proper fs_count.
> 
> Has this been carefully tested with more than just ext4?  If so, which?
ext4 only by xfstests, fs_mark, postmark, ffsb, dbench and sysbench. But
I can try xfs later. I will update you with the test result.

Thanks
Tao
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