On 5/2/06, Jared Hulbert <[email protected]> wrote:
> Nice, this is the first time I heard of anyone using filemap_xip on MTD.
Actually we don't use the MTD. Well, we may use it to provide the
physical address of the volume, thats not really _using_ it.
Can you explain a bit more? If you aren't going to use the MTD, why
rely on it at all?
>> - Design allows for tighter packing of data and higher performance
>> than XIP cramfs
>
> why? by how much?
Data packing:
1) When mkcramfs is writing files to the image it mixes compress and
XIP files. XIP files are page aligned. Compressed files are not. I
think it was about 3.3% wasted I measured on an actual production
linux phone.
2) Choosing page by page to XIP or compress means you can save space,
but it depends on what is more precious, RAM or Flash, given real
designs (ie - you don't buy 36MiB of RAM you get 32MiB or 64MiB)
Performance:
1) The way we are storing the metadata should make for quicker access.
2) Being able to store specific pages of RO data from an otherwise XIP
file such that they end up in RAM has speed thing up for us a great
deal in the lab.
Have you done comparisons vs. squashfs at all? It does better at both
performance and compression that cramfs, so I'm curious.
josh
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