linux-kernel - Re: [PATCH] ext4: fix suboptimal seek

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Message-ID: <87a937d32d.fsf@openvz.org>
Date:	Mon, 01 Dec 2014 14:25:46 +0300
From:	Dmitry Monakhov <dmonakhov@...nvz.org>
To:	Theodore Ts'o <tytso@....edu>
Cc:	linux-kernel@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: fix suboptimal seek_{data,hole} extents traversial

Theodore Ts'o <tytso@....edu> writes:

> On Fri, Nov 28, 2014 at 06:02:02PM +0300, Dmitry Monakhov wrote:
>> FYI: inline_data feature is fatally broken
>
> Thanks for finding the bugs!
>
>> 2) ext4_inline_data_fiemap(0 ignores start and len arguments from ext4_filemap()
>>    which obviously result in endless loop for anyone who want to use
>>    fiemap for inline files (which my patch try to do)
>
> Would this have been triggered using filefrag?  I just checked and
> noticed we don't have a filefrag test in xfstests; of course it would
> be impossible to test other than the filefrag -v command successfully
> completed, but maybe it might be worth adding such a test.
This works only because filefrag use big buffer. If one want to call
fiemap with start != 0 it will loop. So we definitely need a regression
test for fiemap. I'll do it.

BTW bug can be spotted even in case of filefrag -v:
#### Create small file with inlined data 
# echo test > /mnt/f1
#### Now boost it's i_size  
# truncate --size 4096000 /mnt/f1
# filefrag -v /mnt/f1
Filesystem cylinder groups approximately 39
File size of /mnt/f1 is 4096000 (1000 blocks of 4096 bytes)
 ext:     logical_offset:        physical_offset: length:   expected:
 flags:
    0:        0.. 4095999:    2762792..   6858791: 4096000:last,not_aligned,inline,eof
    /mnt/f1: 1 extent found
###According to fiemap we are inlined 4Mb data. :)

At this moment I'm testing my patches, I'll send it today.
>
> 	       	     	      	       	      	   - Ted

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