[Ocfs2-tools-devel] [PATCH 0/4] defrag.ocfs2

[tristan]

Hi goldwyn,

Per my understanding,

pass1 disclaim the unused inode block groups back to global bitmap, the 
intention here is to leave more contiguous space in gb, and pass3 
therefore can perfrom a better defragmentation, right?

One question, why not also disclaim the unused extent block groups?

pass2 is packing the dirents from one extent to another, the sliding 
windows method looks awesome:)


pass3 is trying to fill the holes in bg by latter extents which fits best.

Am I understanding these in a wrong way?

And goldwyn,

I'm also wondering if you've got some interesting benchmark data during 
your lab testing to show the power of patch persuasively;)

Per my testing, I'm sorry to say that I even found a negative effect 
brought by your patches:(

==============================================
Fs without defrag
==============================================
Blocksize: 4096 bytes
Clustersize: 4096 bytes
Total clusters: 7325632
Free clusters: 6811198 (93.0%)

Min. free extent: 2044 KB
Max. free extent: 129020 KB
Avg. free extent: 120552 KB

Chunksize: 1048576 bytes (256 clusters)
Total chunks: 28616
Free chunks: 26381 (92.2%)

HISTOGRAM OF FREE EXTENT SIZES:
Extent Size Range : Free extents Free Clusters Percent
1M... 2M- : 1 511 0.01%
2M... 4M- : 2 1668 0.02%
4M... 8M- : 9 13815 0.20%
8M... 16M- : 2 7614 0.11%
32M... 64M- : 2 32254 0.47%
64M... 128M- : 210 6755336 99.18%


==============================================
Fs after defrag
==============================================
Blocksize: 4096 bytes
Clustersize: 4096 bytes
Total clusters: 7325632
Free clusters: 6811198 (93.0%)

Min. free extent: 4 KB
Max. free extent: 129020 KB
Avg. free extent: 101280 KB

Chunksize: 1048576 bytes (256 clusters)
Total chunks: 28616
Free chunks: 26379 (92.2%)

HISTOGRAM OF FREE EXTENT SIZES:
Extent Size Range : Free extents Free Clusters Percent
4K... 8K- : 1 1 0.00%
8K... 16K- : 3 8 0.00%
16K... 32K- : 9 50 0.00%
32K... 64K- : 5 48 0.00%
64K... 128K- : 6 135 0.00%
128K... 256K- : 6 294 0.00%
256K... 512K- : 8 725 0.01%
512K... 1024K- : 2 292 0.00%
1M... 2M- : 2 846 0.01%
2M... 4M- : 3 2414 0.04%
4M... 8M- : 8 11752 0.17%
8M... 16M- : 2 7443 0.11%
16M... 32M- : 1 7022 0.10%
32M... 64M- : 4 52979 0.78%
64M... 128M- : 209 6727189 98.77%


Disk layout reported by 'o2info' show us that the fs was even more 
fragmented after being defraged.


Anyway, I'll take much closer look on your 3 patches in detail.


Regards,
Tristan.

Goldwyn Rodrigues wrote:
> These patches adds a new tool to defrag ocfs2 filesystem.
> There are 3 passes - 
> Pass 1: Clears unused inode groups
> Pass 2: Defrags the directories, coalescing the directory entries
> Pass 3: Defrags the filesystem as a whole
>
> I haven't done defraging of files (merging of file extents) as yet.
> Algorithms and limitations are in patch headers of the pass they introduce.
>
> Disclaimer: Don't blame me if it eats your data ;)
>
> Comments/Suggestions welcome.
>
>