du result is smaller than xfs_quota report

[Dave Chinner]

On Wed, Oct 21, 2015 at 04:09:20PM +0800, YeYin wrote:
> Hi, Dave,
> Thank you very much. I got some results:
> # xfs_db -xr  /dev/sda4                        
> xfs_db> convert agno 1 agino 78272 ino
> 0x800131c0 (2147561920)
> xfs_db> inode 2147561920
> xfs_db> p
> core.magic = 0x494e
> core.mode = 0100600
> core.version = 2
> core.format = 2 (extents)
> core.nlinkv2 = 0
....
> However, I want to ask how this situation to happen?

Either O_TMPFILE files that are still open, or files that have been
unlinked but still have an open file descriptor referencing them.
They won't be unlinked until the last reference goes away.

> # tail -f /data/test.data &
> [1] 27598
> # unlink /data/test.data 
> 
> 
> # xfs_db -xr -c 'inode 29409295' -c p /dev/sda4
> core.magic = 0x494e
> core.mode = 0100644
> core.version = 2
> core.format = 2 (extents)
> core.nlinkv2 = 1

Inode hasn't been written back to disk yet. That happens
asynchronously, usually based on time, sometimes sooner due to log
space demands, sometimes longer due to repeated modifications.

Cheers,

Dave.
-- 
Dave Chinner
david at fromorbit.com