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btrfs: call btrfs_check_rw_degradable only if there is a missing device

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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>
This commit is contained in:
Anand Jain 2021-10-19 18:43:38 +08:00 committed by David Sterba
parent e77fbf9903
commit 5c78a5e7aa
1 changed files with 2 additions and 1 deletions
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3
fs/btrfs/disk-io.c
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@ -3563,7 +3563,8 @@ 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;