| Message ID | 20180517065829.24906-1-ethanlien@synology.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Thu, May 17, 2018 at 02:58:29PM +0800, Ethan Lien wrote: > 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> > --- > > V2: > Add comment and performance test. Thanks, I maybe edit the comments further as do not feel like I understand why the shortcut can be safely taken just from reading it, but the code looks ok otherwise. I'll add the patch to for-next. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index d241285a0d2a..177630337108 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -1373,6 +1373,13 @@ static noinline int run_delalloc_nocow(struct inode *inode, btrfs_file_extent_encryption(leaf, fi) || btrfs_file_extent_other_encoding(leaf, fi)) goto out_check; + /* + * We can skip the checking of generation of + * extent item in btrfs_cross_ref_exist(). + */ + if (btrfs_file_extent_generation(leaf, fi) <= + btrfs_root_last_snapshot(&root->root_item)) + goto out_check; if (extent_type == BTRFS_FILE_EXTENT_REG && !force) goto out_check; if (btrfs_extent_readonly(fs_info, disk_bytenr)) @@ -7368,6 +7375,14 @@ noinline int can_nocow_extent(struct inode *inode, u64 offset, u64 *len, btrfs_file_extent_other_encoding(leaf, fi)) goto out; + /* + * We can skip the checking of generation of + * extent item in btrfs_cross_ref_exist(). + */ + if (btrfs_file_extent_generation(leaf, fi) <= + btrfs_root_last_snapshot(&root->root_item)) + goto out; + backref_offset = btrfs_file_extent_offset(leaf, fi); if (orig_start) {
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> --- V2: Add comment and performance test. fs/btrfs/inode.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+)