Re: xfs_repair segfaults with ag_stride option

From: Eric Sandeen <sandeen@sandeen.net>
To: Tom Crane <T.Crane@rhul.ac.uk>
Cc: Christoph Hellwig <hch@infradead.org>, xfs@oss.sgi.com
Subject: Re: xfs_repair segfaults with ag_stride option
Date: Mon, 06 Feb 2012 07:21:32 -0600	[thread overview]
Message-ID: <4F2FD3DC.3030301@sandeen.net> (raw)
In-Reply-To: <4F2FB72B.9010209@rhul.ac.uk>

On 2/6/12 5:19 AM, Tom Crane wrote:
> Eric Sandeen wrote:

...

>> Newer tools are fine to use on older filesystems, there should be no
>>   
> 
> Good!
> 
>> issue there.
>>
>> running fsr can cause an awful lot of IO, and a lot of file reorganization.
>> (meaning, they will get moved to new locations on disk, etc).
>>
>> How bad is it, really?  How did you arrive at the 40% number?  Unless
>>   
> 
> xfs_db -c frag -r <block device>

which does:

                answer = (double)(extcount_actual - extcount_ideal) * 100.0 /
                         (double)extcount_actual;

If you work it out, if every file was split into only 2 extents, you'd have
"50%" - and really, that's not bad.  40% is even less bad.

> Some users on our compute farm with large jobs (lots of I/O) find they take longer than with some of our other scratch arrays hosted on other machines.  We also typically find many nfsd tasks in an uninterruptible wait state (sync_page), waiting for data to be copied in from the FS.

So fragmentation may not be the problem... 

-Eric

>> you see perf problems which you know you can attribute to fragmentation,
>> I might not worry about it.
>>
>> You can also check the fragmentation of individual files with the
>> xfs_bmap tool.
>>
>> -Eric
>>   
> 
> Thanks for your advice.
> Cheers
> Tom.
> 
>>  
>>> Tom.
>>>
>>> Christoph Hellwig wrote:
>>>    
>>>> Hi Tom,
>>>>
>>>> On Wed, Feb 01, 2012 at 01:36:12PM +0000, Tom Crane wrote:
>>>>  
>>>>      
>>>>> Dear XFS Support,
>>>>>    I am attempting to use xfs_repair to fix a damaged FS but always
>>>>> get a segfault if and only if -o ag_stride is specified. I have
>>>>> tried ag_stride=2,8,16 & 32.  The FS is approx 60T. I can't find
>>>>> reports of this particular problem on the mailing list archive.
>>>>> Further details are;
>>>>>
>>>>> xfs_repair version 3.1.7, recently downloaded via git repository.
>>>>> uname -a
>>>>> Linux store3 2.6.18-274.17.1.el5 #1 SMP Wed Jan 11 11:10:32 CET 2012
>>>>> x86_64 x86_64 x86_64 GNU/Linux
>>>>>             
>>>> Thanks for the detailed bug report.
>>>>
>>>> Can you please try the attached patch?
>>>>
>>>>         
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>>>     
>>
>>   
> 

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