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Re: garbage collect



On Sun, 25 Jun 2000, Jason Gunthorpe wrote:
> > Yes. In our products we have one read-only filesystem and one r-w system,
> > so we dont get the problem you describe below.
> 
> Oh, I see.. Since there isn't currently any way to partition MTD devices I
> guess you are using multiple physical devices?

We don't use the MTD system - we have our own flash device with
partitioning. Written before we knew about mtd.

> > Yeah, you dont even need to store the mapping in the flash either because
> > the scan does not care if it scans in weird order. 
> 
> Wow, excellent.

However you'd need to make sure the write-node function knows about sector
alignment, so it breaks nodes that span non-consecutive sectors. Same
procedure as when writing to the flash-end.

> Your ciruclar log can give really good leveling because with a formula
> like the above you will be able to swap 'read only' data into high erase
> count blocks!

We have a guy working with JFFS diagnosis tools right now - among others
a way to graphically see the access and GC patterns. When it's in a
useable state I guess we'll include that in the jffs distro as well.

Finn (who is the main JFFS coder) is out of country right now so the
sector spreading has to wait some weeks, unless someone else can do it. I
don't think it would be very hard, provided that the node-breakup is done
in a fashion that can learn to understand sector alignment instead of
partition alignment.

-Bjorn