Cached NAND reads and UBIFS

[Richard Weinberger]

Am 14.07.2016 um 10:33 schrieb Boris Brezillon:
>>> Now we're not sure what do do, should we implement bulk reading in the TNC
>>> code or improve NAND read caching?  
>>
>> Seems like we should improve the caching, either in a layer above, or
>> just in the NAND layer.
> 
> I think we all agree on that one :).

Today I found some time to implement a PoC of a single page cache directly
in UBI.
IMHO UBI is the right layer for that. NAND is too low and UBIFS too high
level.
With a few lines of case I was able to speedup UBIFS TNC lookups a lot,
in fact it gave me the same speed up as caching in the NAND layer does.

As next step I'll tidy the code, add a debugfs interface to expose cache hit/miss
counters such that we can experiment with different workloads and users ontop
of UBIFS. /me thinks of squashfs+ubiblock which is also rather common these days.

Maybe caching more than one page helps too.

Thanks,
//richard