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Re: Anyone using mtd on NAND flash?



On Wed, 13 Sep 2000, David Woodhouse wrote:
> We're already intending to stop JFFS from treating the flash as a single 
> linear device, and start keeping a list of erase blocks in various 
> conditions (full,dirty,empty,etc.). It wouldn't be difficult to handle bad 
> blocks once that's done.

Speaking of that, is there anyone who's actually looking at it yet ? :) 

We've had some emails about what metric to use to decide when a block
should be reused (based on wear-leveling, aging of data etc) but no actual
code suggestions.. 

It would be good to have because it means we can use JFFS for partitions
with a lot of RO-data without having that RO data rotated around the flash
each GC.

The consequence of that is that at least RO decompression of nodes would
be possible, thus making JFFS usable for what cramfs in 2.4 does now - a
really big step forward.

List Of Things To Do to make this work (might not be complete):

   * Node-writing in JFFS should never cross a sector/block boundary (just
     as it does not wrap around a node at the end of the flash today)

   * When we read the end of a block, instead of automatically picking the
     next block, we ask a new function "get_next_usable_block()" or
     whatever, which does the lookup using the reuse-metric etc...

   * The GC should make the join/split choices according to the stuff I
     wrote in a mail a month ago, to make certain no lockups can occur.

Finn are you looking at any of this ? 

-Bjorn