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Message-ID: <20111021202911.GA1633@x4.trippels.de> Date: Fri, 21 Oct 2011 22:29:11 +0200 From: Markus Trippelsdorf <markus@...ppelsdorf.de> To: Christoph Hellwig <hch@...radead.org> Cc: Simon Kirby <sim@...tway.ca>, linux-kernel@...r.kernel.org, xfs@....sgi.com Subject: Re: XFS read hangs in 3.1-rc10 On 2011.10.21 at 09:22 -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. > > 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. > > 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: Please not that he saw this in 3.1-rc10, too. And this version already contains the fixes: % git describe --contains 0030807c66f0582 v3.1-rc10~5^2 I just saw similar symptoms while running a weekly rsync backup job. The machine was stuck for a few seconds several times during that time (no response to mouse or keyboard input). It always recovered by itself after a short while. This is an example output of latencytop during the rsync run: Cause Maximum Percentage [xfs_reclaim_inodes_ag] 7847.0 msec 16.6 % Fork() system call 7777.1 msec 25.5 % Creating block layer request 5352.5 msec 18.1 % [xfs_buf_iowait] 2000.4 msec 14.7 % [down] 959.7 msec 2.0 % Page fault 637.3 msec 1.4 % [xfs_iunpin_wait] 557.4 msec 0.7 % Unlinking file 66.8 msec 0.1 % I also took some "perf timechart" recordings. If there is interest I could post the svg images somewhere. -- Markus -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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