jffs zlib tuning

[Benjamin M. Schwartz]

On Mon, 2008-01-07 at 13:08 -0500, Bernardo Innocenti wrote:
> Note that we compress 4KB blocks in jffs2.  With small block sizes,
> algorithms with better compression tend to loose most of their
> advantage.
> 
> We can't say much until we benchmark lzo vs gzip with small
> files.

Nonetheless, I decided to benchmark the compressors on
http://xs-dev.laptop.org/~cscott/olpc/streams/joyride/build1513/devel_jffs2/xo-1-olpc-stream-joyride-build-1513-20080105_1602-devel_jffs2-tree.tar.bz2

Results:
Uncompressed             732M
LZO -1 (fast)            345M
LZO -9 (slow)            298M
Gzip (defaults)          269M
Bzip2 (as downloaded)    236M

Note that fast vs. slow refers to compression speed.  Decompression is
the same speed in either case.

These tests were run on the whole tar-file.  As noted by Bernie, the
differences would likely be smaller on 4KB blocks.

--Ben