posix_fallocate

[Eric Sandeen]

Krzysztof Błaszkowski wrote:
> 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.

It'd be great if you could test a more recent kernel.

sysrq-t would give us all the backtraces, except I suppose not for the
running process...

I can try to scrape up >16T to test on at some point ...

-Eric