[Cluster-devel] Recording extents in GFS2

[Bob Peterson <rpeterso@redhat.com>]

----- Original Message -----
> On Thu, Feb 25, 2021 at 7:48 PM Bob Peterson <rpeterso@redhat.com> wrote:
> 
> > ----- Original Message -----
> > > >> once we change the journal format, in addition to recording block
> > numbers
> > > >> as extents, there are some additional issues we should address at the
> > same
> > > >> time:
> >
> > One thing I've always thought we should improve upon was the way we manage
> > our bitmaps. Right now, if you allocate or free a block, unless it's on the
> > first block of the rgrp, we need to write two blocks: (1) One for the
> > bitmap
> > that needs to change and, (2) Another for the rgrp to adjust its allocated
> > and
> > free numbers. The rgrplvb code will make this faster, but it would be nice
> > if
> > we would somehow keep "version 2" bitmaps such that each keeps its own
> > statistics.
> >
> > That way we only need to journal and write the affected bitmap, and not
> > necessarily its rgrp block as well. I could see us keep separate glocks
> > for each bitmap, for example, and allowing multiple nodes to work on the
> > same portion of the file system, but on unique bitmaps.
> >
> 
> On the other hand, we currently only need to look at the first block of
> each resource group to figure out if a resource group is suitable for an
> allocation. If we move that information into the bitmap blocks, we'll have
> to look at each of those blocks instead. That's not going to improve our
> performance.
> 
> Andreas
> 
The LVBs will shield us from that, but they won't shield us from having
to rewrite 2 blocks instead of 1.

Bob