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Date:	Fri, 16 Oct 2009 07:17:40 +0000 (GMT)
From:	Holger Kiehl <Holger.Kiehl@....de>
To:	linux-raid <linux-raid@...r.kernel.org>
cc:	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Raid reconstructing and process hanging in D state

Hello

I have a SW Raid6 over 8 disk with a plain 2.6.31.4 kernel. When the
raid is reconstructed I get a lot of process hanging for a long time
in D-state. In fact /var/log/messages shows the following errors:

    Oct 16 04:09:01 hermes kernel: md: data-check of RAID array md3
    Oct 16 04:09:01 hermes kernel: md: minimum _guaranteed_  speed: 1000 KB/sec/disk.
    Oct 16 04:09:01 hermes kernel: md: data-check of RAID array md1
    Oct 16 04:09:01 hermes kernel: md: minimum _guaranteed_  speed: 1000 KB/sec/disk.
    Oct 16 04:09:01 hermes kernel: md: using maximum available idle IO bandwidth (but not more than 200000 KB/sec) for data-check.
    Oct 16 04:09:01 hermes kernel: md: using maximum available idle IO bandwidth (but not more than 200000 KB/sec) for data-check.
    Oct 16 04:09:01 hermes kernel: md: using 128k window, over a total of 70613632 blocks.
    Oct 16 04:09:01 hermes kernel: md: using 128k window, over a total of 70613632 blocks.
    Oct 16 04:09:01 hermes kernel: md: delaying data-check of md0 until md3 has finished (they share one or more physical units)
    Oct 16 04:09:01 hermes kernel: md: delaying data-check of md2 until md0 has finished (they share one or more physical units)
    Oct 16 04:09:01 hermes kernel: md: delaying data-check of md0 until md3 has finished (they share one or more physical units)
    Oct 16 04:09:01 hermes kernel: md: data-check of RAID array md4
    Oct 16 04:09:01 hermes kernel: md: minimum _guaranteed_  speed: 1000 KB/sec/disk.
    Oct 16 04:09:01 hermes kernel: md: using maximum available idle IO bandwidth (but not more than 200000 KB/sec) for data-check.
    Oct 16 04:09:01 hermes kernel: md: using 128k window, over a total of 292413440 blocks.
    Oct 16 04:12:06 hermes kernel: INFO: task pdflush:409 blocked for more than 120 seconds.
    Oct 16 04:12:06 hermes kernel: "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
    Oct 16 04:12:06 hermes kernel: pdflush       D ffff8800280910e8     0   409      2 0x00000000
    Oct 16 04:12:06 hermes kernel: ffff88083ced7aa0 0000000000000046 0000000000000000 ffffea001cc87148
    Oct 16 04:12:06 hermes kernel: ffff88083ced7a80 ffffffff81107530 ffff88083c57e6f8 000000000000e0e8
    Oct 16 04:12:06 hermes kernel: ffff88083c57e6f8 0000000000011c80 0000000000011c80 00000001037141e6
    Oct 16 04:12:06 hermes kernel: Call Trace:
    Oct 16 04:12:06 hermes kernel: [<ffffffff81107530>] ? __block_write_full_page+0x200/0x2f2
    Oct 16 04:12:06 hermes kernel: [<ffffffff81182376>] start_this_handle+0x2dc/0x3b1
    Oct 16 04:12:06 hermes kernel: [<ffffffff8107fb43>] ? autoremove_wake_function+0x0/0x5a
    Oct 16 04:12:06 hermes kernel: [<ffffffff811825ee>] jbd2_journal_start+0xb2/0x101
    Oct 16 04:12:06 hermes kernel: [<ffffffff81167fe5>] ext4_journal_start_sb+0x62/0xa1
    Oct 16 04:12:06 hermes kernel: [<ffffffff8115c051>] ext4_da_writepages+0x1f1/0x430
    Oct 16 04:12:06 hermes kernel: [<ffffffff810734d5>] ? lock_timer_base+0x3a/0x78
    Oct 16 04:12:06 hermes kernel: [<ffffffff810b3816>] do_writepages+0x35/0x5b
    Oct 16 04:12:06 hermes kernel: [<ffffffff810fec80>] writeback_single_inode+0x17c/0x37e
    Oct 16 04:12:06 hermes kernel: [<ffffffff810a30b4>] ? delayacct_end+0x8c/0xad
    Oct 16 04:12:06 hermes kernel: [<ffffffff810ff366>] generic_sync_sb_inodes+0x2b4/0x451
    Oct 16 04:12:06 hermes kernel: [<ffffffff810ff644>] writeback_inodes+0x95/0xfe
    Oct 16 04:12:06 hermes kernel: [<ffffffff810b3a36>] wb_kupdate+0xbb/0x142
    Oct 16 04:12:06 hermes kernel: [<ffffffff810b4917>] ? pdflush+0x0/0x22b
    Oct 16 04:12:06 hermes kernel: [<ffffffff810b4a47>] pdflush+0x130/0x22b
    Oct 16 04:12:06 hermes kernel: [<ffffffff810b397b>] ? wb_kupdate+0x0/0x142
    Oct 16 04:12:06 hermes kernel: [<ffffffff8107f71f>] kthread+0x9b/0xa3
    Oct 16 04:12:06 hermes kernel: [<ffffffff8102ccaa>] child_rip+0xa/0x20
    Oct 16 04:12:06 hermes kernel: [<ffffffff8107f684>] ? kthread+0x0/0xa3
    Oct 16 04:12:06 hermes kernel: [<ffffffff8102cca0>] ? child_rip+0x0/0x20
    Oct 16 04:12:06 hermes kernel: INFO: task kjournald2:2166 blocked for more than 120 seconds.
    Oct 16 04:12:06 hermes kernel: "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
    Oct 16 04:12:06 hermes kernel: kjournald2    D ffff8800280c50e8     0  2166      2 0x00000000
    Oct 16 04:12:06 hermes kernel: ffff8808392cdcd0 0000000000000046 0000000000000000 ffffffff81058376
    Oct 16 04:12:06 hermes kernel: 0000000000000000 ffff88083930b0a0 ffff88083a2b4a38 000000000000e0e8
    Oct 16 04:12:06 hermes kernel: ffff88083a2b4a38 0000000000011c80 0000000000011c80 0000000103713338
    Oct 16 04:12:06 hermes kernel: Call Trace:
    Oct 16 04:12:06 hermes kernel: [<ffffffff81058376>] ? __wake_up_common+0x58/0xa2
    Oct 16 04:12:06 hermes kernel: [<ffffffff811829f3>] jbd2_journal_commit_transaction+0x189/0x10e6
    Oct 16 04:12:06 hermes kernel: [<ffffffff8105aee5>] ? __dequeue_entity+0x41/0x5d
    Oct 16 04:12:06 hermes kernel: [<ffffffff8102a527>] ? __switch_to+0xce/0x2af
    Oct 16 04:12:06 hermes kernel: [<ffffffff8106118d>] ? finish_task_switch+0x6d/0x116
    Oct 16 04:12:06 hermes kernel: [<ffffffff810734d5>] ? lock_timer_base+0x3a/0x78
    Oct 16 04:12:06 hermes kernel: [<ffffffff8107fb43>] ? autoremove_wake_function+0x0/0x5a
    Oct 16 04:12:06 hermes kernel: [<ffffffff81073577>] ? try_to_del_timer_sync+0x64/0x82
    Oct 16 04:12:06 hermes kernel: [<ffffffff81187505>] kjournald2+0x10e/0x23f
    Oct 16 04:12:06 hermes kernel: [<ffffffff8107fb43>] ? autoremove_wake_function+0x0/0x5a
    Oct 16 04:12:06 hermes kernel: [<ffffffff811873f7>] ? kjournald2+0x0/0x23f
    Oct 16 04:12:06 hermes kernel: [<ffffffff8107f71f>] kthread+0x9b/0xa3
    Oct 16 04:12:06 hermes kernel: [<ffffffff8102ccaa>] child_rip+0xa/0x20
    Oct 16 04:12:06 hermes kernel: [<ffffffff8107f684>] ? kthread+0x0/0xa3
    Oct 16 04:12:06 hermes kernel: [<ffffffff8102cca0>] ? child_rip+0x0/0x20

Lowering the reconstruction rate to 10000 in
/proc/sys/dev/raid/speed_limit_max solved the problem. But I was under
the impression that the raid code would lower this speed (to speed_limit_min?)
automatically when there are other process trying to access the device.
Are the other parameters one can tune so that the reconstruction does
not eat all the IO?

Thanks,
Holger
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