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When using a zoned realtime device, tightly packing of data blocks belonging to multiple closed files into the same realtime group (RTG) is very efficient at improving write performance. This is especially true with SMR HDDs as this can reduce, and even suppress, disk head seeks. However, such tight packing does not make sense for large files that require at least a full RTG. If tight packing placement is applied for such files, the VM writeback thread switching between inodes result in the large files to be fragmented, thus increasing the garbage collection penalty later when the RTG needs to be reclaimed. This problem can be avoided with a simple heuristic: if the size of the inode being written back is at least equal to the RTG size, do not use tight-packing. Modify xfs_zoned_pack_tight() to always return false in this case. With this change, a multi-writer workload writing files of 256 MB on a file system backed by an SMR HDD with 256 MB zone size as a realtime device sees all files occupying exactly one RTG (i.e. one device zone), thus completely removing the heavy fragmentation observed without this change. Signed-off-by: Damien Le Moal <dlemoal@kernel.org> Reviewed-by: Darrick J. Wong <djwong@kernel.org> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Carlos Maiolino <cem@kernel.org>
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 reStructuredText 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.