Hi all,
This patches set was born after some discussion between me, Zygo and Josef.
Some details can be found in https://github.com/btrfs/btrfs-todo/issues/19.
Some further information about a real use case can be found in
https://lore.kernel.org/linux-btrfs/20210116002533.ge31...@hungrycats.org/
The idea behind this patches set, is to dedicate some disks (the fastest one)
to the metadata chunk. My initial idea was a "soft" hint. However Zygo
asked an option for a "strong" hint (== mandatory). The result is that
each disk can be "tagged" by one of the following flags:
- BTRFS_DEV_ALLOCATION_METADATA_ONLY
- BTRFS_DEV_ALLOCATION_PREFERRED_METADATA
- BTRFS_DEV_ALLOCATION_PREFERRED_DATA
- BTRFS_DEV_ALLOCATION_DATA_ONLY
When the chunk allocator search a disks to allocate a chunk, scans the disks
in an order decided by these tags. For metadata, the order is:
*_METADATA_ONLY
*_PREFERRED_METADATA
*_PREFERRED_DATA
The *_DATA_ONLY are not eligible from metadata chunk allocation.
For the data chunk, the order is reversed, and the *_METADATA_ONLY are
excluded.
The exact sort logic is to sort first for the "tag", and then for the space
available. If there is no space available, the next "tag" disks set are
selected.
To set these tags, a new property called "allocation_hint" was created.
There is a dedicated btrfs-prog patches set [[PATCH V5] btrfs-progs:
allocation_hint disk property].
$ sudo mount /dev/loop0 /mnt/test-btrfs/
$ for i in /dev/loop[0-9]; do sudo ./btrfs prop get $i allocation_hint; done
devid=1, path=/dev/loop0: allocation_hint=PREFERRED_METADATA
devid=2, path=/dev/loop1: allocation_hint=PREFERRED_METADATA
devid=3, path=/dev/loop2: allocation_hint=PREFERRED_DATA
devid=4, path=/dev/loop3: allocation_hint=PREFERRED_DATA
devid=5, path=/dev/loop4: allocation_hint=PREFERRED_DATA
devid=6, path=/dev/loop5: allocation_hint=DATA_ONLY
devid=7, path=/dev/loop6: allocation_hint=METADATA_ONLY
devid=8, path=/dev/loop7: allocation_hint=METADATA_ONLY
$ sudo ./btrfs fi us /mnt/test-btrfs/
Overall:
Device size: 2.75GiB
Device allocated: 1.34GiB
Device unallocated: 1.41GiB
Device missing: 0.00B
Used: 400.89MiB
Free (estimated): 1.04GiB (min: 1.04GiB)
Data ratio: 2.00
Metadata ratio: 1.00
Global reserve: 3.25MiB (used: 0.00B)
Multiple profiles: no
Data,RAID1: Size:542.00MiB, Used:200.25MiB (36.95%)
/dev/loop0 288.00MiB
/dev/loop1 288.00MiB
/dev/loop2 127.00MiB
/dev/loop3 127.00MiB
/dev/loop4 127.00MiB
/dev/loop5 127.00MiB
Metadata,single: Size:256.00MiB, Used:384.00KiB (0.15%)
/dev/loop1 256.00MiB
System,single: Size:32.00MiB, Used:16.00KiB (0.05%)
/dev/loop0 32.00MiB
Unallocated:
/dev/loop0 704.00MiB
/dev/loop1 480.00MiB
/dev/loop2 1.00MiB
/dev/loop3 1.00MiB
/dev/loop4 1.00MiB
/dev/loop5 1.00MiB
/dev/loop6 128.00MiB
/dev/loop7 128.00MiB
# change the tag of some disks
$ sudo ./btrfs prop set /dev/loop0 allocation_hint DATA_ONLY
$ sudo ./btrfs prop set /dev/loop1 allocation_hint DATA_ONLY
$ sudo ./btrfs prop set /dev/loop5 allocation_hint METADATA_ONLY
$ for i in /dev/loop[0-9]; do sudo ./btrfs prop get $i allocation_hint; done
devid=1, path=/dev/loop0: allocation_hint=DATA_ONLY
devid=2, path=/dev/loop1: allocation_hint=DATA_ONLY
devid=3, path=/dev/loop2: allocation_hint=PREFERRED_DATA
devid=4, path=/dev/loop3: allocation_hint=PREFERRED_DATA
devid=5, path=/dev/loop4: allocation_hint=PREFERRED_DATA
devid=6, path=/dev/loop5: allocation_hint=METADATA_ONLY
devid=7, path=/dev/loop6: allocation_hint=METADATA_ONLY
devid=8, path=/dev/loop7: allocation_hint=METADATA_ONLY
$ sudo btrfs bal start --full-balance /mnt/test-btrfs/
$ sudo ./btrfs fi us /mnt/test-btrfs/
Overall:
Device size: 2.75GiB
Device allocated: 735.00MiB
Device unallocated: 2.03GiB
Device missing: 0.00B
Used: 400.72MiB
Free (estimated): 1.10GiB (min: 1.10GiB)
Data ratio: 2.00
Metadata ratio: 1.00
Global reserve: 3.25MiB (used: 0.00B)
Multiple profiles: no
Data,RAID1: Size:288.00MiB, Used:200.19MiB (69.51%)
/dev/loop0 288.00MiB
/dev/loop1 288.00MiB
Metadata,single: Size:127.00MiB, Used:336.00KiB (0.26%)
/dev/loop5 127.00MiB
System,single: Size:32.00MiB, Used:16.00KiB (0.05%)
/dev/loop7 32.00MiB
Unallocated:
/dev/loop0 736.00MiB
/dev/loop1 736.00MiB
/dev/loop2 128.00MiB
/dev/loop3 128.00MiB
/dev/loop4 128.00MiB
/dev/loop5 1.00MiB
/dev/loop6 128.00MiB
/dev/loop7 96.00MiB
#As you can see all the metadata were placed on the disk loop5/loop7 even if
#the most empty one are loop0 and loop1.
TODO:
- more tests
- the tool which show the space available should consider the tagging (
the disks tagged by _METADATA_ONLY should be excluded from the data
availability)
Comments are welcome
BR
G.Baroncelli
--
gpg @keyserver.linux.it: Goffredo Baroncelli <kreijackATinwind.it>
Key fingerprint BBF5 1610 0B64 DAC6 5F7D 17B2 0EDA 9B37 8B82 E0B5
Revision:
V7:
- make more room in the struct btrfs_ioctl_dev_properties up to 1K
- leave in btrfs_tree.h only the costants
- removed the mount option (sic)
- correct an 'use before check' in the while loop (signaled
by Zygo)
- add a 2nd sort to be sure that the device_info array is in the
expected order
V6:
- add further values to the hints: add the possibility to
exclude a disk for a chunk type
btrfs: add ioctl BTRFS_IOC_DEV_PROPERTIES.
btrfs: add flags to give an hint to the chunk allocator
btrfs: export dev_item.type in
/sys/fs/btrfs/<uuid>/devinfo/<devid>/type
btrfs: add allocator_hint mode
fs/btrfs/ioctl.c | 68 ++++++++++++++++++++++++++
fs/btrfs/sysfs.c | 11 +++++
fs/btrfs/volumes.c | 86 ++++++++++++++++++++++++++++++++-
fs/btrfs/volumes.h | 3 ++
include/uapi/linux/btrfs.h | 39 +++++++++++++++
include/uapi/linux/btrfs_tree.h | 14 ++++++
6 files changed, 219 insertions(+), 2 deletions(-)
