GFS2: Use lvbs for storing rgrp information with mount option
----- Original Message -----
| Instead of reading in the resource groups when gfs2 is checking
| for free space to allocate from, gfs2 can store the necessary
| in the resource group's lvb. Also, instead of searching for unlinked
| inodes in every resource group that's checked for free space, gfs2
| store the number of unlinked but inodes in the lvb, and only check
| unlinked inodes if it will find some.
| The first time a resource group is locked, the lvb must initialized.
| Since this involves counting the unlinked inodes in the resource
| this takes a little extra time. But after that, if the resource
| is locked with GL_SKIP, the buffer head won't be read in unless it's
| actually needed.
| Enabling the resource groups lvbs is done via the rgrplvb mount
| option. If
| this option isn't set, the lvbs will still be set and updated, but
| they won't
| be verfied or used by the filesystem. To safely turn on this option,
| all of
| the nodes mounting the filesystem must be running code with this
| patch, and
| the filesystem must have been completely unmounted since they were
| Signed-off-by: Benjamin Marzinski <firstname.lastname@example.org>