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Subject: Re: Interest in DOC and YAFFS? --> YAFFS bootloading
From: Russ Dill <Russ.Dill@asu.edu>
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> > > A question, though.  I've been doing compression tests with cramfs.
> > > I'm finding that gzip -9 of an ext2 filesystem produces smaller images
> > > than mkcramfs.  Have you ever compared the two?
> > 
> > cramfs is meant to be lean, fast, and low on ram consumption, if you
> > compress the whole thing at once, you have to load the whole thing into
> > ram to read any of it, so cramfs compresses PAGE_CACHE (4096) sized
> > pages at a time
> 
> That's what isn't clear.  I made two filesystems with the same
> contents.  One cramfs and the other ext2.  The ext2 filesystem
> compressed was smaller than the cramfs.  My understanding is that both
> must be uncompressed into a ramfs to be used.  If this is correct,
> then the only comparable consideration is the size of the compressed
> data.

no, a cramfs does not need to be loaded into a ramfs, only the pages
that are needed are loaded from the cramfs, and if memory is in a pinch,
fs pages can be dropped. If you gzip a 4M file at once, vs gzip 4096
byte pieces of it at a time, the former will end up smaller. (deflate
uses repetition of information, and runs of things).

of course, it depends which you want, greatly optimized memory usage
(cramfs), or a slightly smaller image.