mkfs.jffs2 min erase block size: 4 vs 8 KiB

[Mike Frysinger]

On Fri, Jun 24, 2011 at 15:20, Artem Bityutskiy wrote:
> On Fri, 2011-06-24 at 13:10 -0400, Mike Frysinger wrote:
>> On Fri, Jun 24, 2011 at 08:07, Artem Bityutskiy wrote:
>> > For SPI flashes the way out is to emulate larger eraseblock sizes on MTD
>> > level. I'd recommend at least 32 KiB.
>>
>> sorry, but emulate how ?
>
> Well, I was thinking about teaching MTD to merge real PEBs and report
> larger EB size up to JFFS2. Probably this could be done via an MTD
> module parameter and/or an ioctl.
>
>>   just tell jffs2 to use an eraseblock size of
>> 32KiB when creating the fs ?
>
> Yes, the other way is to teach JFFS2 to merge PEBs and work with
> multiple of PEBs. In fact in the past it could do this, but that was
> removed because of some issues, do not remember what.
>
> The only complication I see is bad blocks. When you merge PEBs and one
> of them is bad, then the good PEBs which are in this merge should be
> treated as bad as well. But this should not be very difficult to do.
>
> On the one hand, teaching JFFS2 deal with small PEBs seems to make more
> sense, on the other hand, doing this on driver level has an advantage -
> you do not have to modify the file-system and you automatically make UBI
> benefit from this - UBI scan time goes down when eraseblocks become
> larger.

this is way above my familiarity with the code base.  i'll just post
patches to update the docs.
-mike