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443c8e2a83
Since commitc40a3d38af("Btrfs: Compute and look up csums based on sectorsized blocks") we do a kmap_atomic() on the contents of a bvec. The code beforec40a3d38afhad the kmap region just around the checksumming too. kmap_atomic() in turn does a preempt_disable() and pagefault_disable(), so we shouldn't map the data for too long. Reduce the time the bvec's page is mapped to when we actually need it. Performance wise it doesn't seem to make a huge difference with a 2 vcpu VM on a /dev/zram device: vanilla patched delta write 17.4MiB/s 17.8MiB/s +0.4MiB/s (+2%) read 40.6MiB/s 41.5MiB/s +0.9MiB/s (+2%) The following fio job profile was used in the comparision: [global] ioengine=libaio direct=1 sync=1 norandommap time_based runtime=10m size=100m group_reporting numjobs=2 [test] filename=/mnt/test/fio rw=randrw rwmixread=70 Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de> Reviewed-by: David Sterba <dsterba@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
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.