tree 1e9b1c83266a9a7b5e55bca309150f2eb8541ff3
parent 9dd03ff0990a839c44ae7ed6fcd1ea3d289d2578
author Darrick J. Wong <djwong@kernel.org> 1641507205 -0800
committer Darrick J. Wong <djwong@kernel.org> 1650341052 -0700

xfs: speed up write operations by using non-overlapped lookups when possible

Reverse mapping on a reflink-capable filesystem has some pretty high
overhead when performing file operations.  This is because the rmap
records for logically and physically adjacent extents might not be
adjacent in the rmap index due to data block sharing.  As a result, we
use expensive overlapped-interval btree search, which walks every record
that overlaps with the supplied key in the hopes of finding the record.

However, profiling data shows that when the index contains a record that
is an exact match for a query key, the non-overlapped btree search
function can find the record much faster than the overlapped version.
Try the non-overlapped lookup first when we're trying to find the left
neighbor rmap record for a given file mapping, which makes unwritten
extent conversion and remap operations run faster if data block sharing
is minimal in this part of the filesystem.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>