Re: Defragmentation Not Working with Directory as Argument

On Monday, January 24, 2011 19:11:07 Mitch Harder wrote:

Defragmentation is not working when a directory is supplied as the
argument.  When a file name is supplied as the argument,
defragmentation works well.
=20
This can be demonstrated as follows:
=20
# mount /dev/sdb2 /mnt/btrfs
# cd /mnt/btrfs/
# cp /usr/src/linux/fs/btrfs/zlib.c  .    (any suitable file will do,
small text files seemed appropriate)
# cp zlib.c fragmented-zlib.c
# btrfs fi sync /mnt/btrfs
# cat zlib.c >> fragmented-zlib.c
# btrfs fi sync /mnt/btrfs
# filefrag zlib.c fragmented-zlib.c
zlib.c: 1 extent found
fragmented-zlib.c: 2 extents found
# btrfs filesystem defragment /mnt/btrfs/
# btrfs fi sync /mnt/btrfs
# filefrag zlib.c fragmented-zlib.c
zlib.c: 1 extent found
fragmented-zlib.c: 2 extents found
=20
Now, supply a filename as the argument
=20
# btrfs filesystem defragment /mnt/btrfs/fragmented-zlib.c
# btrfs fi sync /mnt/btrfs
# filefrag zlib.c fragmented-zlib.c
zlib.c: 1 extent found
fragmented-zlib.c: 1 extent found
=20
I've also tested defragmentation on my normal btrfs filesystems, and
have seen the same results.  I've never seen a file defragmented when
using a directory as the argument.

That's because this defragments only directory metadata.

Also, I was wondering if one of the Btrfs developers could clarify th=

e

intended scope of defragmentation when a directory is supplied as the
argument.

I submited apropriate patches few days back to update man and help mess=
ages

I have seen comments on the mailing list indicating that only the
directory supplied is intended to be defragmented, and defragmentatio=

n

will not recurse to subdirectories below.

that's true

However, if I look at the code, and read the documentation for the
older btrfsctl command (which seems to be the basis for the current
btrfs command), it seems like the intention is to recursively
defragment the entire tree below the directory supplied in the
argument.

Then it looks like the userspace part of implementation changed, don't =
know=20
why though.

Regards,
--=20
Hubert Kario
QBS - Quality Business Software
02-656 Warszawa, ul. Ksawer=F3w 30/85
tel. +48 (22) 646-61-51, 646-74-24
www.qbs.com.pl
--
To unsubscribe from this list: send the line "unsubscribe linux-btrfs" =
in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html