Re: UBIFS: How to reserve space to be used right before power cut

[Helmut Raiger <helmut.raiger@hale.at>]

On 06/17/2013 11:02 AM, Helmut Raiger wrote:
> I digged the UBI sources and still have the feeling this won't work:
>
> 1) There seems to be no way to (long term) protect a PEB from being
> moved by the wear leveling sub-system (even scrubbing on bit-flips,
> which may be induced by read-disturbances (reads on nearby pages)).
>
> 2) Temporary protection of a PEB is not really time specific, but depends
> on global PEB erase action (i.e. anything UBIFS does on the same device),
> which is something I can't control.
>
> My impression is, that UBI simply does not support this sort of
> application well. Unmoveable blocks will have a low erase count
> (below average), which is exactly what the WL should avoid.
>
> However I've never timed such a move operation:
> a) move content to a new unused PEB
> b) schedule original PEB for erasure
> It might fit into my timing requirements, but will probably be heavily
> influenced by system load and priorities.
>
> Helmut

Just an update to 'enlight the world'. We are moving to YAFFS2, it has a
deterministic garbage collector which makes it a lot easier to implement
the requested behaviour.
It seems we can even take it off the shelf, currently we are perfomance
testing the write timing.

Helmut


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