In nocow path, we check if the extent is snapshotted in
btrfs_cross_ref_exist(). We can do the similar check earlier and avoid
unnecessary search into extent tree.
A fio test on a Intel D-1531, 16GB RAM, SSD RAID-5 machine as follows:
[global]
group_reporting
time_based
thread=1
ioengine=libaio
bs=4k
iodepth=32
size=64G
runtime=180
numjobs=8
rw=randwrite
[file1]
filename=/mnt/nocow/testfile
IOPS result: unpatched patched
1 fio round: 46670 46958
snapshot
2 fio round: 51826 54498
3 fio round: 59767 61289
After snapshot, the first fio get about 5% performance gain. As we
continually write to the same file, all writes will resume to nocow mode
and eventually we have no performance gain.
Signed-off-by: Ethan Lien <ethanlien@synology.com>
Reviewed-by: David Sterba <dsterba@suse.com>
[ update comments ]
Signed-off-by: David Sterba <dsterba@suse.com>
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