Re: [RFC] Advanced XIP File System

[Jan Engelhardt]

> What is it?:
> - Borrows much from CRAMFS with Linear XIP patches

Apropos borrowing: borrow the compression from Squashfs.

> I've heard people say, "XIP is stupid.  Why on earth would I use
> expensive slow flash instead of cheap fast RAM?"
> [...]  If I
> take libfoo.so which is about 2MiB and throw it in JFFS2, it
> compresses to about 1MiB in flash.  If I store libfoo.so as an XIP
> file (uncompressed) in XIP CRAMFS or AXFS it takes up 2MiB of flash. That is
> 1MiB extra flash for XIP.  But the JFFS2 version would need
> 2MiB of RAM to store that library when used while the XIP system uses
> 0MiB. That means XIP uses +1MiB of flash and -2MiB of RAM for
> libfoo.so.  So for any extra flash used for XIP, it can save twice
> that amount of RAM.  The end result can be lower cost systems on the
> small end.  The secret is to choose what to make XIP and what to
> compress on flash.

If 2 MB of RAM are cheaper [as you say] than 1 MB of Flash, where's the 
advantage when XIP uses more flash?


Jan Engelhardt
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