[ext2fs][patch] reallocblks

[Pedro F. Giffuni]

--- On Tue, 3/15/11, gnehzuil <gnehzuil at gmail.com> wrote:
...
> Hi there,
> 
> I have implemented reallocblks in ext2fs. I added some
> structures in m_ext2fs to record cluster summary information
> due to group descriptor has not a structure to record these
> data in disk. So I implemented it in memory. The
> implementation is almost the same to in ffs.
> 
> I have done some simple benchmarks with dbench. This patch
> can improve the performance a little.
>

I should mention here that this approach (used by FFS) has
shown to be a little better than the reservation window
preallocation in performance and is specially important
to control fragmentation and filesystem aging: an area
that hasn't been worked on very much on other filesystems
(notably ext2/3/4).

This is loosely related to, and reduces the need for, some
other "features" planned in ext4 like delayed allocation,
online defragmentation, preallocation and to some extent
tailmerging.

For more discussion on this topic from a non-BSD
perspective, check out:

http://www-stud.rbi.informatik.uni-frankfurt.de/~loizides/reiserfs/

I am really glad to see this feature in our ext2
implementation. so thanks Zheng for doing the hard work,
and Google for sponsoring him.

cheers,

Pedro.