On 2019/12/5 上午10:58, Zygo Blaxell wrote: > 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? Shrink also takes use of balance, so I see no reason why it won't work on such use cases. > I think there needs to be > a check added for fatal signals for those to work, as they don't respond > to balance cancel. That's a good extra idea. Since we have that wrapper, it would be easier to add in the future. Thanks, Qu > >> 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 >>
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