[Cluster-devel] Recording extents in GFS2

[Abhijith Das <adas@redhat.com>]

Hi all,

With a recent set of patches, we nearly eliminated the per_node statfs
change files by recording that info in the journal. The files and some
recovery code remain only for backward compatibility. Similarly, I'd
like to get rid of the per_node quota change files and record that
info in the journal as well.

I've been talking to Andreas and Bob a bit about this and I'm
investigating how we can record extents as we allocate and deallocate
blocks instead of writing whole blocks. I'm looking into how XFS does
this.

We could have a new journal block type that adds a list of extents to
inodes with alloc/dealloc info. We could add in quota (uid/gid) info
to this as well. If we can do this right, the representation of
alloc/dealloc becomes compact and consequently we use journal space
more efficiently. We can hopefully avoid cases where we need to zero
out blocks during allocation as well.

I'm sending this out to start a discussion and to get ideas/comments/pointers.

Cheers!
--Abhi