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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> Reviewed-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Christoph Hellwig <hch@lst.de>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.