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Subject: What do the "wait_current_trans" messages mean I see on my raspberry pi?
From: Clemens Eisserer <linuxhippy@gmail.com>
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Hi,

Over the weekend I tried to copy one external usb drive (on ext4) to
another one formatted with btrfs.
Now I came back, and 48h later only ~300GB were copied and I found
messages like the following on syslog:

May 16 18:33:13 raspberrypi kernel: [ 8161.213142] btrfs-endio-wri D
c0420f24     0  3593      2 0x00000000
May 16 18:33:13 raspberrypi kernel: [ 8161.213735] [<c0420f24>]
(__schedule+0x288/0x568) from [<bf24f488>]
(wait_current_trans+0xcc/0x13c [btrfs])
May 16 18:33:13 raspberrypi kernel: [ 8161.214357] [<bf24f488>]
(wait_current_trans+0xcc/0x13c [btrfs]) from [<bf250e68>]
(start_transaction+0x2d8/0x43c [btrfs])
May 16 18:33:13 raspberrypi kernel: [ 8161.214956] [<bf250e68>]
(start_transaction+0x2d8/0x43c [btrfs]) from [<bf2510c0>]
(btrfs_join_transaction+0x20/0x2c [btrfs])
May 16 18:33:13 raspberrypi kernel: [ 8161.215562] [<bf2510c0>]
(btrfs_join_transaction+0x20/0x2c [btrfs]) from [<bf25a334>]
(btrfs_finish_ordered_io+0x2c4/0x5b0 [btrfs])
May 16 18:33:13 raspberrypi kernel: [ 8161.216233] [<bf25a334>]
(btrfs_finish_ordered_io+0x2c4/0x5b0 [btrfs]) from [<bf28473c>]
(worker_loop+0x150/0x674 [btrfs])
May 16 18:33:13 raspberrypi kernel: [ 8161.216631] [<bf28473c>]
(worker_loop+0x150/0x674 [btrfs]) from [<c003a120>]
(kthread+0xa4/0xb0)
May 16 18:33:13 raspberrypi kernel: [ 8161.218363] [<c003a120>]
(kthread+0xa4/0xb0) from [<c000e218>] (ret_from_fork+0x14/0x3c)

More of them are available at: http://pastebin.com/th9tuSas

Any idea what they mean? Are they related to the slow speed I observed?

Thank you in advance, Clemens