On Fri, Oct 21, 2011 at 09:22:40AM -0400, Christoph Hellwig wrote: > On Thu, Oct 20, 2011 at 03:42:14PM -0700, Simon Kirby wrote: > > > > [<ffffffff8126f205>] xfs_reclaim_inode+0x85/0x2b0 > > [<ffffffff8126f5b0>] xfs_reclaim_inodes_ag+0x180/0x2f0 > > [<ffffffff8126f74e>] xfs_reclaim_inodes_nr+0x2e/0x40 > > [<ffffffff8126ccf0>] xfs_fs_free_cached_objects+0x10/0x20 > > [<ffffffff81119a70>] prune_super+0x110/0x1b0 > > [<ffffffff810e4fa5>] shrink_slab+0x1e5/0x2a0 > > [<ffffffff810e5821>] kswapd+0x7c1/0xba0 > > [<ffffffff8107ada6>] kthread+0x96/0xb0 > > [<ffffffff816c0474>] kernel_thread_helper+0x4/0x10 > > [<ffffffffffffffff>] 0xffffffffffffffff > > We're stuck in synchronous inode reclaim. > > > All of the other processes that get stuck have this stack: > > > > [<ffffffff81080587>] down+0x47/0x50 > > [<ffffffff8125e816>] xfs_buf_lock+0x66/0xd0 > > [<ffffffff812603ad>] _xfs_buf_find+0x16d/0x270 > > [<ffffffff81260517>] xfs_buf_get+0x67/0x1a0 > > [<ffffffff8126067a>] xfs_buf_read+0x2a/0x120 > > [<ffffffff812b876f>] xfs_trans_read_buf+0x28f/0x3f0 > > [<ffffffff8129e161>] xfs_read_agi+0x71/0x100 > > They are waiting for the AGI buffer to become unlocked. The only reason > it is held locked for longer time is when it is under I/O. > > > > > By the way, xfs_reclaim_inode+0x85 (133) disassembles as: > > > > > ...So the next function is wait_for_completion(), which is marked > > __sched and thus doesn't show up in the trace. > > So we're waiting for the inode to be flushed, aka I/O again. But I don't seem to see any queued I/O, hmm. > What is interesting here is that we're always blocking on the AGI > buffer - which is used during unlinks of inodes, and thus gets hit > fairly heavily for a workload that does a lot of unlinks. I don't think we do too many unlinks, but there are quite a bit of renames over existing files (dovecot-2.0 w/mdbox). > > When the clog happens, "iostat -x -k 1" shows no reads from the XFS > > devices, though writes keep happening. "vmstat 1" matches. I tried > > switching schedulers from CFQ to deadline -- no difference. Queue depth > > is empty on the devices and nothing is actually clogged up at the device > > -- it's not actually plugged at the controller or disk. I did a sysreq-w > > while this was happening. About 10 seconds later, everything unclogs and > > continues. Sysreq-W output below. I poked around at the various XFS > > tracepoints in /sys/kernel/debug/tracing/events/xfs, but I'm not sure > > which tracepoints to use and many of them scroll too fast to see > > anything. Any suggestions? > > Given that you are doing a lot of unlinks I wonder if it is related > to the recent ail pushing issues in that area. While your symptoms > looks completely different we could be blocking on the flush completion > for an inode that gets stuck in the AIL. > > Can you run with latest 3.0-stable plus the patches at: > > http://oss.sgi.com/pipermail/xfs/2011-October/053464.html > > If this doesn't help I'll probably need to come up with some tracing > patches for you. It seemes 3.0.7+gregkh's stable-queue queue-3.0 patches seems to be running fine without blocking at all on this SSD box, so that should narrow it down significantly. Hmm, looking at git diff --stat v3.0.7..v3.1-rc10 fs/xfs , maybe not.. :) Maybe 3.1 fs/xfs would transplant into 3.0 or vice-versa? Simon- _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
