Re: [iPAQ] Battery Life, Flash Writing, etc...

Compression is a Real Big Thing.

In many ways, the flash size is more of a constraint than RAM.

This is not to say /usr should not be put on a diet: we have alot we
can and should do here.

I just note that people are attempting to put 100 pounds into the 10
pound bag we have: making that bag size effectively closer to 20 pounds
will make alot more people happy. We note that the people keeping the
Skiff systems buisest seem to be those with the most code to cram into
the bag (e.g. the Helix folks).

Note we don't need compression on the fly: in fact, in operation, we believe
PDA's are most likely to be storing already compressed data into flash
(e.g. JPEG's from cameras, audio streams, etc.), so just being able to
read executables and shared libraries from compressed form (paging out
of compressed data) will go a long way: we don't want compression enabled
by default (we believe that applications should give a hint to the file
system whether it would be useful or not). Since doing compression twice
eats batteries, we really want to avoid double compression scenarios.

So to start, a static operation performed to compress files up front is
just fine, in our opinion. The real pain of cramfs is always having to
do it, and reflash the whole file system. My experience on Itsy was that life
got SOO much easier once we had a flash file system running, and we could
just update individual files (even if uncompressed).

Without compression, we'll still be using cramfs indefinately, IMHO.
                                        - Jim

--
Jim Gettys
Technology and Corporate Development
Compaq Computer Corporation
jg@pa.dec.com