btrfs: call btrfs_check_rw_degradable only if there is a missing device

commit 5c78a5e7aa835c4f08a7c90fe02d19f95a776f29 upstream.

In open_ctree() in btrfs_check_rw_degradable() [1], we check each block
group individually if at least the minimum number of devices is available
for that profile. If all the devices are available, then we don't have to
check degradable.

[1]
open_ctree()
::
3559 if (!sb_rdonly(sb) && !btrfs_check_rw_degradable(fs_info, NULL)) {

Also before calling btrfs_check_rw_degradable() in open_ctee() at the
line number shown below [2] we call btrfs_read_chunk_tree() and down to
add_missing_dev() to record number of missing devices.

[2]
open_ctree()
::
3454         ret = btrfs_read_chunk_tree(fs_info);

btrfs_read_chunk_tree()
  read_one_chunk() / read_one_dev()
    add_missing_dev()

So, check if there is any missing device before btrfs_check_rw_degradable()
in open_ctree().

Also, with this the mount command could save ~16ms.[3] in the most
common case, that is no device is missing.

[3]
 1) * 16934.96 us | btrfs_check_rw_degradable [btrfs]();

CC: stable@vger.kernel.org # 4.19+
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 355ea88d5c5f72113924e3bb891c89dcbe9d342b..6965ed081346281fdc950e985c7012d4dcd32408 100644 (file)
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -3556,7 +3556,8 @@ int __cold open_ctree(struct super_block *sb, struct btrfs_fs_devices *fs_device
                goto fail_sysfs;
        }
 
-       if (!sb_rdonly(sb) && !btrfs_check_rw_degradable(fs_info, NULL)) {
+       if (!sb_rdonly(sb) && fs_info->fs_devices->missing_devices &&
+           !btrfs_check_rw_degradable(fs_info, NULL)) {
                btrfs_warn(fs_info,
                "writable mount is not allowed due to too many missing devices");
                goto fail_sysfs;