posix_fallocate

["Krzysztof Błaszkowski" <kb@sysmikro.com.pl>]

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.


Regards,
Krzysztof Blaszkowski

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