fallocate bug?

[Zhu Han]

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:

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

$ 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

$ du -h --apparent-size file
1.1G    file

$du -h file
2.0G

best regards,
韩竹(Zhu Han)
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