Re: [PATCH 00/22 take 3] UBI: Unsorted Block Images

Thomas Gleixner
2007-03-21T11:18:24Z

On Wed, 2007-03-21 at 12:05 +0100, Jörn Engel wrote:
> On Tue, 20 March 2007 01:42:46 +0100, Thomas Gleixner wrote:
> > On Mon, 2007-03-19 at 17:32 -0500, Matt Mackall wrote:
> >
> > > > > 4. JFFS2 has its own wear-leving scheme, as do several other
> > > > > filesystems, so they probably want to bypass this piece of the stack.
> > > >
> > > > JFFS2 on top of UBI delegates the wear levelling to UBI, as JFFS2s own
> > > > wear levelling sucks.
> > >
> > > Ok, fine. How about LogFS, then?
> >
> > LogFS can easily leverage UBI's wear algorithm.
>
> Ok, now we have reached the absurd. UBI quite fundamentally cannot do
> wear leveling as good as LogFS can. Simply because UBI has zero
> knowledge of the _contents_ of its blocks. Knowing whether a block is
> 90% garbage or not makes a great difference.
>
> Also LogFS currently requires erasesizes of 2^n.

Last time I talked to you about that, you said it would be possible and
fixable. We talked about several mechanisms, which would allow a
filesystem or other users to hint such things to UBI.

Even if the LogFS wear levelling is so superior, it CAN'T do across
device wear levelling.

tglx