Hello, we have got some issues with I/O in our kvm environment. We are using kernel version 2.6.32 (Ubuntu 10.04 LTS) to virtualise our hosts and we are using ksm, too. Recently we noticed that sometimes the guest systems (mainly OpenSuse guest systems) suddenly have a read only filesystem. After some inspection we found out that the guest system generates some ata errors due to timeouts (mostly in "flush cache" situations). On the physical host there are always the same kernel messages when this happens: """ [1508127.195469] INFO: task kjournald:497 blocked for more than 120 seconds. [1508127.212828] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [1508127.246841] kjournald D 00000000ffffffff 0 497 2 0x00000000 [1508127.246848] ffff88062128dba0 0000000000000046 0000000000015bc0 0000000000015bc0 [1508127.246855] ffff880621089ab0 ffff88062128dfd8 0000000000015bc0 ffff8806210896f0 [1508127.246862] 0000000000015bc0 ffff88062128dfd8 0000000000015bc0 ffff880621089ab0 [1508127.246868] Call Trace: [1508127.246880] [<ffffffff8116e500>] ? sync_buffer+0x0/0x50 [1508127.246889] [<ffffffff81557d87>] io_schedule+0x47/0x70 [1508127.246893] [<ffffffff8116e545>] sync_buffer+0x45/0x50 [1508127.246897] [<ffffffff8155825a>] __wait_on_bit_lock+0x5a/0xc0 [1508127.246901] [<ffffffff8116e500>] ? sync_buffer+0x0/0x50 [1508127.246905] [<ffffffff81558338>] out_of_line_wait_on_bit_lock +0x78/0x90 [1508127.246911] [<ffffffff810850d0>] ? wake_bit_function+0x0/0x40 [1508127.246915] [<ffffffff8116e6c6>] __lock_buffer+0x36/0x40 [1508127.246920] [<ffffffff81213d11>] journal_submit_data_buffers +0x311/0x320 [1508127.246924] [<ffffffff81213ff2>] journal_commit_transaction +0x2d2/0xe40 [1508127.246931] [<ffffffff810397a9>] ? default_spin_lock_flags +0x9/0x10 [1508127.246935] [<ffffffff81076c7c>] ? lock_timer_base+0x3c/0x70 [1508127.246939] [<ffffffff81077719>] ? try_to_del_timer_sync+0x79/0xd0 [1508127.246943] [<ffffffff81217f0d>] kjournald+0xed/0x250 [1508127.246947] [<ffffffff81085090>] ? autoremove_wake_function +0x0/0x40 [1508127.246951] [<ffffffff81217e20>] ? kjournald+0x0/0x250 [1508127.246954] [<ffffffff81084d16>] kthread+0x96/0xa0 [1508127.246959] [<ffffffff810141ea>] child_rip+0xa/0x20 [1508127.246962] [<ffffffff81084c80>] ? kthread+0x0/0xa0 [1508127.246966] [<ffffffff810141e0>] ? child_rip+0x0/0x20 [1508127.246969] INFO: task flush-251:0:505 blocked for more than 120 seconds. [1508127.264076] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [1508127.298343] flush-251:0 D ffffffff810f4370 0 505 2 0x00000000 [1508127.298349] ffff880621fdba30 0000000000000046 0000000000015bc0 0000000000015bc0 [1508127.298354] ffff88062108b1a0 ffff880621fdbfd8 0000000000015bc0 ffff88062108ade0 [1508127.298358] 0000000000015bc0 ffff880621fdbfd8 0000000000015bc0 ffff88062108b1a0 [1508127.298362] Call Trace: [1508127.298370] [<ffffffff810f4370>] ? sync_page+0x0/0x50 [1508127.298375] [<ffffffff81557d87>] io_schedule+0x47/0x70 [1508127.298379] [<ffffffff810f43ad>] sync_page+0x3d/0x50 [1508127.298383] [<ffffffff8155825a>] __wait_on_bit_lock+0x5a/0xc0 [1508127.298391] [<ffffffff810f4347>] __lock_page+0x67/0x70 [1508127.298395] [<ffffffff810850d0>] ? wake_bit_function+0x0/0x40 [1508127.298402] [<ffffffff810f4487>] ? unlock_page+0x27/0x30 [1508127.298410] [<ffffffff810fd9dd>] write_cache_pages+0x3bd/0x4d0 [1508127.298417] [<ffffffff810fc670>] ? __writepage+0x0/0x40 [1508127.298425] [<ffffffff810fdb14>] generic_writepages+0x24/0x30 [1508127.298432] [<ffffffff810fdb55>] do_writepages+0x35/0x40 [1508127.298439] [<ffffffff811668a6>] writeback_single_inode+0xf6/0x3d0 [1508127.298449] [<ffffffff812b81d6>] ? rb_erase+0xd6/0x160 [1508127.298455] [<ffffffff8116750e>] writeback_inodes_wb+0x40e/0x5e0 [1508127.298462] [<ffffffff811677ea>] wb_writeback+0x10a/0x1d0 [1508127.298469] [<ffffffff81077719>] ? try_to_del_timer_sync+0x79/0xd0 [1508127.298477] [<ffffffff8155803d>] ? schedule_timeout+0x19d/0x300 [1508127.298485] [<ffffffff81167b1c>] wb_do_writeback+0x18c/0x1a0 [1508127.298493] [<ffffffff81167b83>] bdi_writeback_task+0x53/0xe0 [1508127.298503] [<ffffffff8110f546>] bdi_start_fn+0x86/0x100 [1508127.298510] [<ffffffff8110f4c0>] ? bdi_start_fn+0x0/0x100 [1508127.298518] [<ffffffff81084d16>] kthread+0x96/0xa0 [1508127.298526] [<ffffffff810141ea>] child_rip+0xa/0x20 [1508127.298533] [<ffffffff81084c80>] ? kthread+0x0/0xa0 [1508127.298541] [<ffffffff810141e0>] ? child_rip+0x0/0x20 ... some more messages like those before... """ Sometimes the message "INFO: task kvm blocked for more than 120 seconds" appears, too. I thought the error happens in cache writeback situations so I started to adjust "/proc/sys/vm/dirty_background_ratio" to 5 and "/proc/sys/vm/dirty_ratio" to 40. I thought this will write continously smaller parts of cached memory to HDD (more often, but smaller chunks). This did not help. There are still "readonly" filesystems in the guest systems. Does anybody has some tips to regulate I/O on linux systems or to stop those "readonly" filesystems? I tried the "cfq" scheduler and did some ionice (best efforts method, all kvm processes in the same class). I thought of cgroups, but I could not find any I/O related properties to set. We are using logical volumes as virtual guest HDDs. The volume group is on top of a mdraid device. Thank you for your help... Best Regards Sebastian -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
