8d2a83a97f
Before deciding if we can do a NOCOW write into a range, one of the things we have to do is check if there are checksum items for that range. We do that through the btrfs_lookup_csums_list() function, which searches for checksums and adds them to a list supplied by the caller. But all we need is to check if there is any checksum, we don't need to look for all of them and collect them into a list, which requires more search time in the checksums tree, allocating memory for checksums items to add to the list, copy checksums from a leaf into those list items, then free that memory, etc. This is all unnecessary overhead, wasting mostly CPU time, and perhaps some occasional IO if we need to read from disk any extent buffers. So change btrfs_lookup_csums_list() to allow to return immediately in case it finds any checksum, without the need to add it to a list and read it from a leaf. This is accomplished by allowing a NULL list parameter and making the function return 1 if it found any checksum, 0 if it didn't found any, and a negative value in case of an error. The following test with fio was used to measure performance: $ cat test.sh #!/bin/bash DEV=/dev/nullb0 MNT=/mnt/nullb0 cat <<EOF > /tmp/fio-job.ini [global] name=fio-rand-write filename=$MNT/fio-rand-write rw=randwrite bssplit=4k/20:8k/20:16k/20:32k/20:64k/20 direct=1 numjobs=16 fallocate=posix time_based runtime=300 [file1] size=8G ioengine=io_uring iodepth=16 EOF umount $MNT &> /dev/null mkfs.btrfs -f $DEV mount -o ssd $DEV $MNT fio /tmp/fio-job.ini umount $MNT The test was run on a release kernel (Debian's default kernel config). The results before this patch: WRITE: bw=139MiB/s (146MB/s), 8204KiB/s-9504KiB/s (8401kB/s-9732kB/s), io=17.0GiB (18.3GB), run=125317-125344msec The results after this patch: WRITE: bw=153MiB/s (160MB/s), 9241KiB/s-10.0MiB/s (9463kB/s-10.5MB/s), io=17.0GiB (18.3GB), run=114054-114071msec Reviewed-by: Qu Wenruo <wqu@suse.com> Signed-off-by: Filipe Manana <fdmanana@suse.com> 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 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.