Re: The value displayed by 'ls -s' command is strange.

[Chris Mason <chris.mason@oracle.com>]

Excerpts from Tsutomu Itoh's message of 2010-12-07 02:59:52 -0500:
> Hi,
> 
> I think that the disk allocation size of each file becomes a monotone increase
> when the file is made.
> But, it sometimes return to 0.  Is it correct?

Well, there's a window during the processing of delayed allocation where
we don't have the bytes recorded as delalloc and we don't have the bytes
recorded in the inode yet.  That's why they are showing up as zero.

We don't call inode_add_bytes() until after we insert the extent, but we
drop the delalloc byte count on the file before the IO is done.

Fixing it will be a little tricky because all the extent accounting
assumes the inode_add_bytes happens at extent insertion time.

-chris

> 
> 
> The result of the test at 2.6.37-rc4 is shown below. 
> (see inode no. 291)
> 
>     # df -T /test14
>     Filesystem    Type   1K-blocks      Used Available Use% Mounted on
>     /dev/sdd14   btrfs     4162560      8736   3709440   1% /test14
>     # dd if=/dev/zero of=/test14/dir/as001.26603 bs=1M count=100
>     # dd if=/dev/zero of=/test14/dir/as002.26603 bs=1M count=200
>     # dd if=/dev/zero of=/test14/dir/sy001.26603 bs=1M count=300 oflag=direct
>     # dd if=/dev/zero of=/test14/dir/as003.26603 bs=1M count=400
>     # ls -lis /test14/dir
>     total 406528
>     288      0 -rw-r--r-- 1 root root 104857600 Dec  7 15:07 as001.26603
>     289      0 -rw-r--r-- 1 root root 209715200 Dec  7 15:07 as002.26603
>  -> 291  99328 -rw-r--r-- 1 root root 419430400 Dec  7 15:08 as003.26603
>     290 307200 -rw-r--r-- 1 root root 314572800 Dec  7 15:08 sy001.26603
>     # sleep 3
>     # ls -lis /test14/dir
>     total 406528
>     288      0 -rw-r--r-- 1 root root 104857600 Dec  7 15:07 as001.26603
>     289      0 -rw-r--r-- 1 root root 209715200 Dec  7 15:07 as002.26603
>  -> 291  99328 -rw-r--r-- 1 root root 419430400 Dec  7 15:08 as003.26603
>     290 307200 -rw-r--r-- 1 root root 314572800 Dec  7 15:08 sy001.26603
>     # sleep 3
>     # ls -lis /test14/dir
>     total 307200
>     288      0 -rw-r--r-- 1 root root 104857600 Dec  7 15:07 as001.26603
>     289      0 -rw-r--r-- 1 root root 209715200 Dec  7 15:07 as002.26603
>  -> 291      0 -rw-r--r-- 1 root root 419430400 Dec  7 15:08 as003.26603
>     290 307200 -rw-r--r-- 1 root root 314572800 Dec  7 15:08 sy001.26603
>     # sleep 3
>     # ls -lis /test14/dir
>     total 409600
>     288 102400 -rw-r--r-- 1 root root 104857600 Dec  7 15:07 as001.26603
>     289      0 -rw-r--r-- 1 root root 209715200 Dec  7 15:07 as002.26603
>  -> 291      0 -rw-r--r-- 1 root root 419430400 Dec  7 15:08 as003.26603
>     290 307200 -rw-r--r-- 1 root root 314572800 Dec  7 15:08 sy001.26603
>     # sync
>     # ls -lis /test14/dir
>     total 1024000
>     288 102400 -rw-r--r-- 1 root root 104857600 Dec  7 15:07 as001.26603
>     289 204800 -rw-r--r-- 1 root root 209715200 Dec  7 15:07 as002.26603
>  -> 291 409600 -rw-r--r-- 1 root root 419430400 Dec  7 15:08 as003.26603
>     290 307200 -rw-r--r-- 1 root root 314572800 Dec  7 15:08 sy001.26603
> 
> The trace result of btrfs_getattr() is shown below. 
> 
>  Dec  7 15:08:03 luna kernel: ino:291 blocks:198656 i_blocks:0 i_bytes:0 delalloc_bytes:101711872
>  Dec  7 15:08:06 luna kernel: ino:291 blocks:198656 i_blocks:0 i_bytes:0 delalloc_bytes:101711872
>  Dec  7 15:08:09 luna kernel: ino:291 blocks:0 i_blocks:0 i_bytes:0 delalloc_bytes:0
>  Dec  7 15:08:12 luna kernel: ino:291 blocks:0 i_blocks:0 i_bytes:0 delalloc_bytes:0
>  Dec  7 15:08:18 luna kernel: ino:291 blocks:819200 i_blocks:819200 i_bytes:0 delalloc_bytes:0
> 
> 
> Regards,
> Itoh
>