[PATCH 0/3] btrfs: More intelligent degraded chunk allocator

Qu Wenruo
2019-11-07T06:27:17Z

This patchset will make btrfs degraded mount more intelligent and
provide more consistent profile keeping function.

One of the most problematic aspect of degraded mount is, btrfs may
create unwanted profiles.

# mkfs.btrfs -f /dev/test/scratch[12] -m raid1 -d raid1
# wipefs -fa /dev/test/scratch2
# mount -o degraded /dev/test/scratch1 /mnt/btrfs
# fallocate -l 1G /mnt/btrfs/foobar
# btrfs ins dump-tree -t chunk /dev/test/scratch1
item 7 key (FIRST_CHUNK_TREE CHUNK_ITEM 1674575872) itemoff 15511 itemsize 80
length 536870912 owner 2 stripe_len 65536 type DATA
New data chunk will fallback to SINGLE or DUP.

The cause is pretty simple, when mounted degraded, missing devices can't
be used for chunk allocation.
Thus btrfs has to fall back to SINGLE profile.

This patchset will make btrfs to consider missing devices as last resort if
current rw devices can't fulfil the profile request.

This should provide a good balance between considering all missing
device as RW and completely ruling out missing devices (current mainline
behavior).

Qu Wenruo (3):
btrfs: volumes: Refactor device holes gathering into a separate
function
btrfs: volumes: Add btrfs_fs_devices::missing_list to collect missing
devices
btrfs: volumes: Allocate degraded chunks if rw devices can't fullfil a
chunk

fs/btrfs/block-group.c | 10 ++-
fs/btrfs/volumes.c | 170 ++++++++++++++++++++++++++---------------
fs/btrfs/volumes.h | 6 ++
3 files changed, 121 insertions(+), 65 deletions(-)

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2.24.0