tree 0a23b42a8d275d3499fac2b90ded76276c64c1c1
parent be283b2e674a09457d4563729015adb637ce7cc1
author Josef Bacik <jbacik@fusionio.com> 1362684124 -0500
committer Josef Bacik <jbacik@fusionio.com> 1367870058 -0400

Btrfs: add a incompatible format change for smaller metadata extent refs

We currently store the first key of the tree block inside the reference for the
tree block in the extent tree.  This takes up quite a bit of space.  Make a new
key type for metadata which holds the level as the offset and completely removes
storing the btrfs_tree_block_info inside the extent ref.  This reduces the size
from 51 bytes to 33 bytes per extent reference for each tree block.  In practice
this results in a 30-35% decrease in the size of our extent tree, which means we
COW less and can keep more of the extent tree in memory which makes our heavy
metadata operations go much faster.  This is not an automatic format change, you
must enable it at mkfs time or with btrfstune.  This patch deals with having
metadata stored as either the old format or the new format so it is easy to
convert.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fusionio.com>