Re: Some JFFS3 feedback

Artem B. Bityutskiy
2005-11-16T14:03:51Z

Hello Charles,

Charles Manning wrote:
> I briefly read the JFFS3 doc, and will read it more. It has some very
> interesting ideas in it.
thanks for your feedback.

> About 9 years back, I did some flash file system patent research and IIRC one
> of the patents covered something very similar to the Wandering Tree approach
> to addressing the write-in-place problem, so there might be some IP issues
> with this. I shall have a scratch around to see if I can find it (though
> finding something in a 20+ year old paper mountain is a challenge).
Hmm, it is interesting. We would be very appreciated if you provide some
information.

> I will be interested to see how you tackle the dreaded garbage collection.
> IMHO, GC is something that needs to be considered sooner rather than later
> because it is key to sustained write performance.
Absolutely. Me and my workmate in OktetLabs are thinking on this. At the
moment we're considering 2 approaches. It seems there are no fundamental
problems, but it needs more thinking, analisys and evaluation. We're
even going to create a user-level prototype to see how well (and fast)
will GC work. Only after I have a clear picture in my mind I'm able to
put it clearly in the paper.

But we anyway are not going to start implementation befor we've designed GC.

> I know that it is hard to change a name, but JFFS3 is really not much like
> JFFS2 or JFFS in design, so keeping a similar name really gets confusing
> later on (I get enough problems with yaffs and yaffs2 and they share 90% of
> the code). I would suggest a name change to avoid confusion down the track.
Hmm, frankly, I think we may consider JFFS3 as an JFFS2's descendant.
Yes, the code is probably going to be completely different. But try to
glance to JFFS3 like this: it is just JFFS2 + on-flash indexing. JFFS2
keeps indexing in RAM, we are going to keep it on Flash. Glance at
figure 5 here:
http://www.linux-mtd.infradead.org/tech/JFFS3design/node8.html.

But if there are some other good names and people are really bothered by
the JFFS3 name - we might rename it as well.

--
Best Regards,
Artem B. Bityutskiy,
St.-Petersburg, Russia.