On Sun, Jun 13, 2010 at 02:50:06PM +0800, Shaohua Li wrote: > On Fri, Jun 11, 2010 at 10:32:07AM +0800, Yan, Zheng wrote: > > On Fri, Jun 11, 2010 at 9:12 AM, Shaohua Li <shaohua.li@xxxxxxxxx> wrote: > > > On Fri, Jun 11, 2010 at 01:41:41AM +0800, Jerome Ibanes wrote: > > >> List, > > >> > > >> I ran into a hang issue (race condition: cpu is high when the server is > > >> idle, meaning that btrfs is hanging, and IOwait is high as well) running > > >> 2.6.34 on debian/lenny on a x86_64 server (dual Opteron 275 w/ 16GB ram). > > >> The btrfs filesystem live on 18x300GB scsi spindles, configured as Raid-0, > > >> as shown below: > > >> > > >> Label: none uuid: bc6442c6-2fe2-4236-a5aa-6b7841234c52 > > >> Total devices 18 FS bytes used 2.94TB > > >> devid 5 size 279.39GB used 208.33GB path /dev/cciss/c1d0 > > >> devid 17 size 279.39GB used 208.34GB path /dev/cciss/c1d8 > > >> devid 16 size 279.39GB used 209.33GB path /dev/cciss/c1d7 > > >> devid 4 size 279.39GB used 208.33GB path /dev/cciss/c0d4 > > >> devid 1 size 279.39GB used 233.72GB path /dev/cciss/c0d1 > > >> devid 13 size 279.39GB used 208.33GB path /dev/cciss/c1d4 > > >> devid 8 size 279.39GB used 208.33GB path /dev/cciss/c1d11 > > >> devid 12 size 279.39GB used 208.33GB path /dev/cciss/c1d3 > > >> devid 3 size 279.39GB used 208.33GB path /dev/cciss/c0d3 > > >> devid 9 size 279.39GB used 208.33GB path /dev/cciss/c1d12 > > >> devid 6 size 279.39GB used 208.33GB path /dev/cciss/c1d1 > > >> devid 11 size 279.39GB used 208.33GB path /dev/cciss/c1d2 > > >> devid 14 size 279.39GB used 208.33GB path /dev/cciss/c1d5 > > >> devid 2 size 279.39GB used 233.70GB path /dev/cciss/c0d2 > > >> devid 15 size 279.39GB used 209.33GB path /dev/cciss/c1d6 > > >> devid 10 size 279.39GB used 208.33GB path /dev/cciss/c1d13 > > >> devid 7 size 279.39GB used 208.33GB path /dev/cciss/c1d10 > > >> devid 18 size 279.39GB used 208.34GB path /dev/cciss/c1d9 > > >> Btrfs v0.19-16-g075587c-dirty > > >> > > >> The filesystem, mounted in /mnt/btrfs is hanging, no existing or new > > >> process can access it, however 'df' still displays the disk usage (3TB out > > >> of 5). The disks appear to be physically healthy. Please note that a > > >> significant number of files were placed on this filesystem, between 20 and > > >> 30 million files. > > >> > > >> The relevant kernel messages are displayed below: > > >> > > >> INFO: task btrfs-submit-0:4220 blocked for more than 120 seconds. > > >> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > > >> btrfs-submit- D 000000010042e12f 0 4220 2 0x00000000 > > >> ffff8803e584ac70 0000000000000046 0000000000004000 0000000000011680 > > >> ffff8803f7349fd8 ffff8803f7349fd8 ffff8803e584ac70 0000000000011680 > > >> 0000000000000001 ffff8803ff99d250 ffffffff8149f020 0000000081150ab0 > > >> Call Trace: > > >> [<ffffffff813089f3>] ? io_schedule+0x71/0xb1 > > >> [<ffffffff811470be>] ? get_request_wait+0xab/0x140 > > >> [<ffffffff810406f4>] ? autoremove_wake_function+0x0/0x2e > > >> [<ffffffff81143a4d>] ? elv_rq_merge_ok+0x89/0x97 > > >> [<ffffffff8114a245>] ? blk_recount_segments+0x17/0x27 > > >> [<ffffffff81147429>] ? __make_request+0x2d6/0x3fc > > >> [<ffffffff81145b16>] ? generic_make_request+0x207/0x268 > > >> [<ffffffff81145c12>] ? submit_bio+0x9b/0xa2 > > >> [<ffffffffa01aa081>] ? btrfs_requeue_work+0xd7/0xe1 [btrfs] > > >> [<ffffffffa01a5365>] ? run_scheduled_bios+0x297/0x48f [btrfs] > > >> [<ffffffffa01aa687>] ? worker_loop+0x17c/0x452 [btrfs] > > >> [<ffffffffa01aa50b>] ? worker_loop+0x0/0x452 [btrfs] > > >> [<ffffffff81040331>] ? kthread+0x79/0x81 > > >> [<ffffffff81003674>] ? kernel_thread_helper+0x4/0x10 > > >> [<ffffffff810402b8>] ? kthread+0x0/0x81 > > >> [<ffffffff81003670>] ? kernel_thread_helper+0x0/0x10 > > > This looks like the issue we saw too, http://lkml.org/lkml/2010/6/8/375. > > > This is reproduceable in our setup. > > > > I think I know the cause of http://lkml.org/lkml/2010/6/8/375. > > The code in the first do-while loop in btrfs_commit_transaction > > set current process to TASK_UNINTERRUPTIBLE state, then calls > > btrfs_start_delalloc_inodes, btrfs_wait_ordered_extents and > > btrfs_run_ordered_operations(). All of these function may call > > cond_resched(). > Hi, > When I test random write, I saw a lot of threads jump into btree_writepages() > and do noting and io throughput is zero for some time. Looks like there is a > live lock. See the code of btree_writepages(): > if (wbc->sync_mode == WB_SYNC_NONE) { > struct btrfs_root *root = BTRFS_I(mapping->host)->root; > u64 num_dirty; > unsigned long thresh = 32 * 1024 * 1024; > > if (wbc->for_kupdate) > return 0; > > /* this is a bit racy, but that's ok */ > num_dirty = root->fs_info->dirty_metadata_bytes; > >>>>>> if (num_dirty < thresh) > return 0; > } > The marked line is quite intrusive. In my test, the live lock is caused by the thresh > check. The dirty_metadata_bytes < 32M. Without it, I can't see the live lock. Not > sure if this is related to the hang. How much ram do you have? The goal of the check is to avoid writing metadata blocks because once we write them we have to do more IO to cow them again if they are changed later. It shouldn't be looping hard in btrfs there, what was the workload? -chris -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
