On Tue, May 06, 2014 at 05:43:24PM +0100, Hugo Mills wrote:
> > >So in my case when I hit that case, I had to use dusage=0 to recover.
> > >Anything above that just didn't work.
> >
> > I suspect when using more than zero the first chunk it wanted to balance
> > wasn't empty - and it had nowhere to put it. Then when you did dusage=0, it
> > didn't need a destination for the data. That is actually an interesting
> > workaround for that case.
>
> I've actually looked into implementing a "smallest=n" filter that
> would taken only the n least-full chunks (by fraction) and balance
> those. However, it's not entirely trivial to do efficiently with the
> current filtering code.
I've prototyped something similar, to limit the number of balanced
chunks by a number. To achieve "n least-full chunks" would be an
iterative process of increasing the usage filter and limiting the number
of chunks until the desired N is reached.
N=n
F=0
while (N > 0) {
balance -dusage=F,limit=N
N -= <number of balanced chunks>
F++
}
The patch is in branch dev/balance-limit in my git repos.
We can then implement the n-least-full as a synthetic filter from
userspace.
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