Update: It seems like btrfs-send is not completely hung. It somewhat regularly wakes up every hour to transfer a few bytes. I noticed this via a periodic 'ls -l' on the snapshot file. These are the last outputs (uniq'ed):
-rw------- 1 root root 1492797759 Sep 6 08:44 intenso_white.snapshot -rw------- 1 root root 1493087856 Sep 6 09:44 intenso_white.snapshot -rw------- 1 root root 1773825308 Sep 6 10:44 intenso_white.snapshot -rw------- 1 root root 1773976853 Sep 6 11:58 intenso_white.snapshot -rw------- 1 root root 1774122301 Sep 6 12:59 intenso_white.snapshot -rw------- 1 root root 1774274264 Sep 6 13:58 intenso_white.snapshot -rw------- 1 root root 1774435235 Sep 6 14:57 intenso_white.snapshot I also monitor the /proc/3022/task/*/stack files with 'tail -f' (I have no idea if this is useful) but there are no changes, even during the short wakeups. Am Do., 6. Sep. 2018 um 11:22 Uhr schrieb Stefan Löwen <stefan.loe...@gmail.com>: > > Hello linux-btrfs, > > I'm trying to clone a subvolume with 'btrfs send' but it always hangs > for hours. > > I tested this on multiple systems. All showed the same result: > - Manjaro (btrfs-progs v4.17.1; linux v4.18.5-1-MANJARO) > - Ubuntu 18.04 in VirtualBox (btrfs-progs v4.15.1; linux v4.15.0-33-generic) > - ArchLinux in VirtualBox (btrfs-progs v4.17.1; linux v4.18.5-arch1-1-ARCH) > All following logs are from the ArchLinux VM. > > To make sure it's not the 'btrfs receive' at fault I tried sending into > a file using the following command: > 'strace -o btrfs-send.strace btrfs send -vvv -f intenso_white.snapshot > /mnt/intenso_white/@data/.snapshots/test-snapshot' > > The 'btrfs send' process always copies around 1.2-1.4G of data, then > stops all disk IO and fully loads one cpu core. btrfs scrub found 0 > errors. Neither did btrfsck. 'btrfs device stats' is all 0. > > I would be thankful for all ideas and tips. > > Regards > Stefan > > --------------------------------------------- > > The btrfs-send.strace is attached. So is the dmesg.log during the hang. > > Stack traces of the hung process: > --- /proc/3022/task/3022/stack --- > [<0>] 0xffffffffffffffff > --- /proc/3022/task/3023/stack --- > [<0>] pipe_wait+0x6c/0xb0 > [<0>] splice_from_pipe_next.part.3+0x24/0xa0 > [<0>] __splice_from_pipe+0x43/0x180 > [<0>] splice_from_pipe+0x5d/0x90 > [<0>] default_file_splice_write+0x15/0x20 > [<0>] __se_sys_splice+0x31b/0x770 > [<0>] do_syscall_64+0x5b/0x170 > [<0>] entry_SYSCALL_64_after_hwframe+0x44/0xa9 > [<0>] 0xffffffffffffffff > > [vagrant@archlinux mnt]$ uname -a > Linux archlinux 4.18.5-arch1-1-ARCH #1 SMP PREEMPT Fri Aug 24 12:48:58 > UTC 2018 x86_64 GNU/Linux > > [vagrant@archlinux mnt]$ btrfs --version > btrfs-progs v4.17.1 > > [vagrant@archlinux mnt]$ sudo btrfs fi show /dev/sdb1 > Label: 'intenso_white' uuid: 07bf61ed-7728-4151-a784-c4b840e343ed > Total devices 1 FS bytes used 655.82GiB > devid 1 size 911.51GiB used 703.09GiB path /dev/sdb1 > > [vagrant@archlinux mnt]$ sudo btrfs fi df /mnt/intenso_white/ > Data, single: total=695.01GiB, used=653.69GiB > System, DUP: total=40.00MiB, used=96.00KiB > Metadata, DUP: total=4.00GiB, used=2.13GiB > GlobalReserve, single: total=512.00MiB, used=0.00B >
