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btrfs: remove unnecessary leaf free space checks when pushing items
When trying to push items from a leaf into its left and right neighbours,
we lock the left or right leaf, check if it has the required minimum free
space, COW the leaf and then check again if it has the minimum required
free space. This second check is pointless:
1) Most and foremost because it's not needed. We have a write lock on the
leaf and on its parent node, so no one can come in and change either
the pre-COW or post-COW version of the leaf for the whole duration of
the push_leaf_left() and push_leaf_right() calls;
2) The call to btrfs_leaf_free_space() is not trivial, it has a fair
amount of arithmetic operations and access to fields in the leaf's
header and items, so it's not very cheap.
So remove the duplicated free space checks.
This change if part of a patchset that is comprised of the following
patches:
1/6 btrfs: remove unnecessary leaf free space checks when pushing items
2/6 btrfs: avoid unnecessary COW of leaves when deleting items from a leaf
3/6 btrfs: avoid unnecessary computation when deleting items from a leaf
4/6 btrfs: remove constraint on number of visited leaves when replacing extents
5/6 btrfs: remove useless path release in the fast fsync path
6/6 btrfs: prepare extents to be logged before locking a log tree path
The last patch in the series has some performance test result in its
changelog.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>