Re: [RFC 0/5] BTRFS hot relocation support

[Stefan Behrens <sbehrens@giantdisaster.de>]

On 05/09/2013 01:13, Zhi Yong Wu wrote:
> HI, all
>
>     I saw that bcache will be merged into kernel upstream soon, so i
> want to know if btrfs hot relocation support is still meanful, if no,
> i will not continue to work on it. can anyone let me know this?
> thanks.

Which one is better?

Please do some measurements. Select typical file system use cases, and 
publish and compare the measurement results of the two approaches.


> On Mon, May 6, 2013 at 4:53 PM,  <zwu.kernel@gmail.com> wrote:
>> From: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
>>
>>    The patchset as RFC is sent out mainly to see if it goes in the
>> correct development direction.
>>
>>    The patchset is trying to introduce hot relocation support
>> for BTRFS. In hybrid storage environment, when the data in
>> HDD disk get hot, it can be relocated to SSD disk by BTRFS
>> hot relocation support automatically; also, if SSD disk ratio
>> exceed its upper threshold, the data which get cold can be
>> looked up and relocated to HDD disk to make more space in SSD
>> disk at first, and then the data which get hot will be relocated
>> to SSD disk automatically.
>>
>>    BTRFS hot relocation mainly reserve block space from SSD disk
>> at first, load the hot data to page cache from HDD, allocate
>> block space from SSD disk, and finally write the data to SSD disk.
>>
>>    If you'd like to play with it, pls pull the patchset from
>> my git on github:
>>    https://github.com/wuzhy/kernel.git hot_reloc
>>
>> For how to use, please refer too the example below:
>>
>> root@debian-i386:~# echo 0 > /sys/block/vdc/queue/rotational
>> ^^^ Above command will hack /dev/vdc to be one SSD disk
>> root@debian-i386:~# echo 999999 > /proc/sys/fs/hot-age-interval
>> root@debian-i386:~# echo 10 > /proc/sys/fs/hot-update-interval
>> root@debian-i386:~# echo 10 > /proc/sys/fs/hot-reloc-interval
>> root@debian-i386:~# mkfs.btrfs -d single -m single -h /dev/vdb /dev/vdc -f
>>
>> WARNING! - Btrfs v0.20-rc1-254-gb0136aa-dirty IS EXPERIMENTAL
>> WARNING! - see http://btrfs.wiki.kernel.org before using
>>
>> [ 140.279011] device fsid c563a6dc-f192-41a9-9fe1-5a3aa01f5e4c devid 1 transid 16 /dev/vdb
>> [ 140.283650] device fsid c563a6dc-f192-41a9-9fe1-5a3aa01f5e4c devid 2 transid 16 /dev/vdc
>> [ 140.517089] device fsid 197d47a7-b9cd-46a8-9360-eb087b119424 devid 1 transid 3 /dev/vdb
>> [ 140.550759] device fsid 197d47a7-b9cd-46a8-9360-eb087b119424 devid 1 transid 3 /dev/vdb
>> [ 140.552473] device fsid c563a6dc-f192-41a9-9fe1-5a3aa01f5e4c devid 2 transid 16 /dev/vdc
>> adding device /dev/vdc id 2
>> [ 140.636215] device fsid 197d47a7-b9cd-46a8-9360-eb087b119424 devid 2 transid 3 /dev/vdc
>> fs created label (null) on /dev/vdb
>> nodesize 4096 leafsize 4096 sectorsize 4096 size 14.65GB
>> Btrfs v0.20-rc1-254-gb0136aa-dirty
>> root@debian-i386:~# mount -o hot_move /dev/vdb /data2
>> [ 144.855471] device fsid 197d47a7-b9cd-46a8-9360-eb087b119424 devid 1 transid 6 /dev/vdb
>> [ 144.870444] btrfs: disk space caching is enabled
>> [ 144.904214] VFS: Turning on hot data tracking
>> root@debian-i386:~# dd if=/dev/zero of=/data2/test1 bs=1M count=2048
>> 2048+0 records in
>> 2048+0 records out
>> 2147483648 bytes (2.1 GB) copied, 23.4948 s, 91.4 MB/s
>> root@debian-i386:~# df -h
>> Filesystem Size Used Avail Use% Mounted on
>> /dev/vda1 16G 13G 2.2G 86% /
>> tmpfs 4.8G 0 4.8G 0% /lib/init/rw
>> udev 10M 176K 9.9M 2% /dev
>> tmpfs 4.8G 0 4.8G 0% /dev/shm
>> /dev/vdb 15G 2.0G 13G 14% /data2
>> root@debian-i386:~# btrfs fi df /data2
>> Data: total=3.01GB, used=2.00GB
>> System: total=4.00MB, used=4.00KB
>> Metadata: total=8.00MB, used=2.19MB
>> Data_SSD: total=8.00MB, used=0.00
>> root@debian-i386:~# echo 108 > /proc/sys/fs/hot-reloc-threshold
>> ^^^ Above command will start HOT RLEOCATE, because The data temperature is currently 109
>> root@debian-i386:~# df -h
>> Filesystem Size Used Avail Use% Mounted on
>> /dev/vda1 16G 13G 2.2G 86% /
>> tmpfs 4.8G 0 4.8G 0% /lib/init/rw
>> udev 10M 176K 9.9M 2% /dev
>> tmpfs 4.8G 0 4.8G 0% /dev/shm
>> /dev/vdb 15G 2.1G 13G 14% /data2
>> root@debian-i386:~# btrfs fi df /data2
>> Data: total=3.01GB, used=6.25MB
>> System: total=4.00MB, used=4.00KB
>> Metadata: total=8.00MB, used=2.26MB
>> Data_SSD: total=2.01GB, used=2.00GB
>> root@debian-i386:~#
>>
>> Zhi Yong Wu (5):
>>    vfs: add one list_head field
>>    btrfs: add one new block group
>>    btrfs: add one hot relocation kthread
>>    procfs: add three proc interfaces
>>    btrfs: add hot relocation support
>>
>>   fs/btrfs/Makefile            |   3 +-
>>   fs/btrfs/ctree.h             |  26 +-
>>   fs/btrfs/extent-tree.c       | 107 +++++-
>>   fs/btrfs/extent_io.c         |  31 +-
>>   fs/btrfs/extent_io.h         |   4 +
>>   fs/btrfs/file.c              |  36 +-
>>   fs/btrfs/hot_relocate.c      | 802 +++++++++++++++++++++++++++++++++++++++++++
>>   fs/btrfs/hot_relocate.h      |  48 +++
>>   fs/btrfs/inode-map.c         |  13 +-
>>   fs/btrfs/inode.c             |  92 ++++-
>>   fs/btrfs/ioctl.c             |  23 +-
>>   fs/btrfs/relocation.c        |  14 +-
>>   fs/btrfs/super.c             |  30 +-
>>   fs/btrfs/volumes.c           |  28 +-
>>   fs/hot_tracking.c            |   1 +
>>   include/linux/btrfs.h        |   4 +
>>   include/linux/hot_tracking.h |   1 +
>>   kernel/sysctl.c              |  22 ++
>>   18 files changed, 1234 insertions(+), 51 deletions(-)
>>   create mode 100644 fs/btrfs/hot_relocate.c
>>   create mode 100644 fs/btrfs/hot_relocate.h