UBI/UBIFS: dealing with MLC's paired pages

[Artem Bityutskiy]

On Fri, 2015-10-30 at 13:30 +0100, Boris Brezillon wrote:
> You're right, but it makes a big difference when all your writes are
> taking longer because you need to run the GC to retrieve a free LEB,
> and
> this is probably what's gonna happen when your FS raises ~1/2 its
> maximum size. Doing it in background (collecting a few valid nodes on
> each GC step and letting user operations take place between each of
> these step) should help mitigating this problem.

It makes difference, yes. However, again, the worst case scenario is
that whenever I need to write, I have do GC, because I am "punished" by
previous writes. The worst case scenario is twice as slow write.

Guaranteed twice as fast wear is the other implication.

Increased power consumption is another one. Not every embedded system
will find the "you have to do a lot of job in background" UBIFS feature
attractive.

Anyway, could you spend a bit more time trying to provide convincing
arguments that doing "skip on demand" is hard, or does not gain
anything. You expressed this opinion, but so far it did not look 100%
convincing.

Thanks!