From 78d4295b1eeed4d857f11333caac8b4894ac4412 Mon Sep 17 00:00:00 2001 From: Ethan Lien Date: Thu, 17 May 2018 14:58:29 +0800 Subject: [PATCH] btrfs: lift some btrfs_cross_ref_exist checks in nocow path 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 Reviewed-by: David Sterba [ update comments ] Signed-off-by: David Sterba --- fs/btrfs/inode.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index 5d370bbdf82659..27293ff7174df1 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -1370,6 +1370,13 @@ 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; + /* + * Do the same check as in btrfs_cross_ref_exist but + * without the unnecessary search. + */ + 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)) @@ -7322,6 +7329,14 @@ noinline int can_nocow_extent(struct inode *inode, u64 offset, u64 *len, btrfs_file_extent_other_encoding(leaf, fi)) goto out; + /* + * Do the same check as in btrfs_cross_ref_exist but without the + * unnecessary search. + */ + 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) {