Approximately 16 hours ago I've run a script that deleted >~100 snapshots and started quota rescan on a large USB-connected btrfs volume (5.4 of 22 TB occupied now). Quota rescan only completed just now, with 100% load from [btrfs-transacti] throughout this period, which is probably ~ok depending on your view on things.

What worries me is innocent process using _another_, SATA-connected btrfs volume that hung right after I started my script and took >30 minutes to be sigkilled. There's nothing interesting in the kernel log, and attempts to attach strace to the process output nothing, but I of course suspect that it freezed on disk operation.

I wonder:
1) Can there be a contention for CPU or some mutexes between kernel btrfs threads belonging to different volumes? 2) If yes, can anything be done about it other than mounting volumes from (different) VMs?


$ uname -a; btrfs --version
Linux host 4.4.0-66-generic #87-Ubuntu SMP Fri Mar 3 15:29:05 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux
btrfs-progs v4.4

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With Best Regards,
Marat Khalili

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