Re: [PATCH 0/4] btrfs: Make balance cancelling response faster

Zygo Blaxell
2019-12-05T02:58:34Z

[-- Attachment #1: Type: text/plain, Size: 2098 bytes --]

On Tue, Dec 03, 2019 at 02:42:50PM +0800, Qu Wenruo wrote:
> [PROBLEM]
> There are quite some users reporting that 'btrfs balance cancel' slow to
> cancel current running balance, or even doesn't work for certain dead
> balance loop.
>
> With the following script showing how long it takes to fully stop a
> balance:
> #!/bin/bash
> dev=/dev/test/test
> mnt=/mnt/btrfs
>
> umount $mnt &> /dev/null
> umount $dev &> /dev/null
>
> mkfs.btrfs -f $dev
> mount $dev -o nospace_cache $mnt
>
> dd if=/dev/zero bs=1M of=$mnt/large &
> dd_pid=$!
>
> sleep 3
> kill -KILL $dd_pid
> sync
>
> btrfs balance start --bg --full $mnt &
> sleep 1
>
> echo "cancel request" >> /dev/kmsg
> time btrfs balance cancel $mnt
> umount $mnt
>
> It takes around 7~10s to cancel the running balance in my test
> environment.
>
> [CAUSE]
> Btrfs uses btrfs_fs_info::balance_cancel_req to record how many cancel
> request are queued.
> However that cancelling request is only checked after relocating a block
> group.
>
> That behavior is far from optimal to provide a faster cancelling.
>
> [FIX]
> This patchset will add more cancelling check points, to make cancelling
> faster.

Nice! I look forward to using this in the future!

Does this cover device delete/resize as well? I think there needs to be
a check added for fatal signals for those to work, as they don't respond
to balance cancel.

> And also, introduce a new error injection points to cover these newly
> introduced and future check points.
>
> Qu Wenruo (4):
> btrfs: relocation: Introduce error injection points for cancelling
> balance
> btrfs: relocation: Check cancel request after each data page read
> btrfs: relocation: Check cancel request after each extent found
> btrfs: relocation: Work around dead relocation stage loop
>
> fs/btrfs/ctree.h | 1 +
> fs/btrfs/relocation.c | 23 +++++++++++++++++++++++
> fs/btrfs/volumes.c | 2 +-
> 3 files changed, 25 insertions(+), 1 deletion(-)
>
> --
> 2.24.0
>

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 195 bytes --]