[PATCH 0/3] Btrfs: save free space cache to the disk V2

[Josef Bacik <josef@redhat.com>]

V1->V2
- This includes my previous fix for the Incompat flags that I posted earlier
- Fix kunmap() to use the page and not the vaddr, I messed this up when going
from kmap_atomic to kmap

This patch series introduces the ability for btrfs to store the free space cache
ondisk to make the caching of a block group much quicker.  Previously we had to
search the entire extent-tree to look for gaps everytime we wanted to allocate
in a block group.  This approach instead dumps all of the free space cache to
disk for every dirtied block group each time we commit the transaction.  This is
a disk format change, but in order to use the feature you will have to mount
with -o space_cache, and then from then on you won't be able to use old kernels
with your filesystem.  You can pull these patches from my git tree

git://git.kernel.org/pub/scm/linux/kernel/git/josef/btrfs-work.git

and they should pull right onto Chris's btrfs-unstable tree.  Please test this
as it's a big change and I can only test so much.  That being said this has been
run through xfstests thoroughly and I've been running it on a VM with btrfs as
root.  Thanks,

Josef