fallocate bug?

[Zhu Han]

On Tue, May 8, 2012 at 7:59 AM, Dave Chinner <david at fromorbit.com> wrote:

> On Mon, May 07, 2012 at 08:44:17PM +0800, Zhu Han wrote:
> > Seems like xfs of CentOS 6.X occupies much more storage space than
> desired
> > if fallocate is used against the file. Here is the step to reproduce it:
>
> You test case is not doing what you think it is doing.
>

Thanks for pointing it out.



>
> > By the way, is it normal when the file is moved around after the
> > preallocated region is filled with data?
> >
> > $ uname -r
> > 2.6.32-220.7.1.el6.x86_64
> >
> > $fallocate -n --offset 0 -l 1G file    ---->Write a little more data than
> > the preallocated size
> >
> > $ xfs_bmap -p -vv file
> > file:
> >  EXT: FILE-OFFSET      BLOCK-RANGE            AG AG-OFFSET
> > TOTAL FLAGS
> >    0: [0..2097151]:    2593408088..2595505239 21 (29420144..31517295)
> > 2097152 10000
> >
> > $ dd if=/dev/zero of=/tmp/file bs=1M count=1026 conv=fsync
>
> That does a truncate first, removing all the preallocated space. Use
> conv=notrunc to avoid this. Hence the space allocated by this
> new write is different to the space allocated by the above
> preallocation. The file has not been moved, the filesystem just did
> what you asked it to do.
>
> >
> > $ xfs_bmap -p -vv file
> > file:
> >  EXT: FILE-OFFSET      BLOCK-RANGE            AG AG-OFFSET
> > TOTAL FLAGS
> >    0: [0..4194303]:    2709184016..2713378319 22 (23101408..27295711)
> > 4194304 00000
>
> And so now you've triggered the speculative delayed allocation
> beyond EOF, which is normal behaviour. Hence there are currently
> unused blocks beyond EOF which will get removed either when the next
> close(fd) occurs on the file or the inode is removed from the cache.
>

Close(fd) should be invoked before dd quits. But why the extra blocks
beyond EOF are not freed?

The only way I found to remove the extra blocks is truncate the file to its
real size.


>
> Cheers,
>
> Dave.
> --
> Dave Chinner
> david at fromorbit.com
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://oss.sgi.com/pipermail/xfs/attachments/20120508/84acd8e3/attachment.htm>