I tested Online Defrag, and seems this feature is still
very unstable.
1)
# mkfs.ext4 -m 0 -b 1024 -O ^flex_bg /dev/sdb7
# mount -t ext4 -o nodelalloc /dev/sdb7 mnt_point
# (age /dev/sdb7 using ffsb)
...
# df
Filesystem 1K-blocks Used Available Use% Mounted on
...
/dev/sdb7 5159829 5118866 40963 100% ...
sdb7 has 40M free space left. And I ran e4defrag on a directory full
of small files (most < 1M), but all failed, and dmesg didn't tell
me the reasion.
# e4defrag mnt_point/data0/
...
[62/1562]/../mnt_point/data0/fillfile1420: 0% [ NG ]
[63/1562]/../mnt_point/data0/fillfile188: 0% [ NG ]
...
Success: [ 0/1562 ]
Failure: [ 1562/1562 ]
# df
Filesystem 1K-blocks Used Available Use% Mounted on
...
/dev/sdb7 5159829 5159807 22 100% ...
Though all failed, but now the 40M free space was occupied, why?
If delalloc is turned on, things are somewhat different, most files can
be defraged, and dmesg told me not enough free blocks for the failure
cases.
2)
I sometimes got panic after defrag a directory:
Dirty block accounting went wrong -8977
Dirty block accounting went wrong -9279
Dirty block accounting went wrong -9718
Dirty block accounting went wrong -10258
...
...
Dirty block accounting went wrong -157352
Dirty block accounting went wrong -157700
EXT4-fs error(device sdb7): ext_mb_free_metadata: Double free of blocks 985 (984 2)
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