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Re: posix_fallocate

To: xfs@xxxxxxxxxxx
Subject: Re: posix_fallocate
From: Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx>
Date: Fri, 07 May 2010 04:23:57 -0500
In-reply-to: <201005071022.37863.kb@xxxxxxxxxxxxxxx>
References: <201005071022.37863.kb@xxxxxxxxxxxxxxx>
User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.9.1.9) Gecko/20100317 Thunderbird/3.0.4
Krzysztof Błaszkowski put forth on 5/7/2010 3:22 AM:
> Hello,
> 
> I use this to preallocate large space but found an issue. Posix_fallocate 
> works right with sizes like 100G, 1T and even 10T on some boxes (on some 
> other can fail after e.g. 7T threshold) but if i tried e.g. 16T the user 
> space process would be "R"unning forever and it is not interruptible. 
> Furthermore some other not related processes like sshd, bash enter D state. 
> There is nothing in kernel log.
> 
> I made so far a few logs with ftrace facility for 1G, 100G, 1T and 10T sizes. 
> I noticed that for 1st three sizes the log is as long as abt 1.5M (2M peak) 
> while 10T generates 94M long log. I couldn't retrieve a log for 17T case 
> because "cat /sys ... /trace" enters D.
> 
> I would appreciate any help because i gave up with ftrace logs analysis. The 
> xfs_vn_fallocate is covered in abt 11k lines for a 1.5M log case while there 
> are abt 163k lines in 94M log. And all i could see is poss some relationship 
> between time spent in xfs_vn_fallocate subfunctions vs requested space.
> 
> Box details:
> 16 Hitachi 2TB drives (backplane connected), dm, 1 lvm lun of 25T size,
> kernel 2.6.31.5, more recent kernels neither xfs were not tested.

32 or 64 bit kernel?  What is the size of the XFS filesystem on the 25TB LVM
LUN against which you're running posix_fallocate?  The reason I ask is that
XFS has a 16TB per filesystem limitation on 32 bit kernels.  I can only
assume that your XFS filesystem is larger than 16TB since you're attempting
to posix_fallocate 16TB.  But, it's best to ask for confirmation rather than
assume, especially given that your problem is appearing near that magical
16TB boundary.

-- 
Stan

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