On Fri, Mar 03, 2017 at 04:52:58PM +0100, Michal Hocko wrote: > On Fri 03-03-17 10:37:21, Brian Foster wrote: > [...] > > That aside, looking through some of the traces in this case... > > > > - kswapd0 is waiting on an inode flush lock. This means somebody else > > flushed the inode and it won't be unlocked until the underlying buffer > > I/O is completed. This context is also holding pag_ici_reclaim_lock > > which is what probably blocks other contexts from getting into inode > > reclaim. > > - xfsaild is in xfs_iflush(), which means it has the inode flush lock. > > It's waiting on reading the underlying inode buffer. The buffer read > > sets b_ioend_wq to the xfs-buf wq, which is ultimately going to be > > queued in xfs_buf_bio_end_io()->xfs_buf_ioend_async(). The associated > > work item is what eventually triggers the I/O completion in > > xfs_buf_ioend(). > > > > So at this point reclaim is waiting on a read I/O completion. It's not > > clear to me whether the read had completed and the work item was queued > > or not. I do see the following in the workqueue lockup BUG output: > > > > [ 273.412600] workqueue xfs-buf/sda1: flags=0xc > > [ 273.414486] pwq 4: cpus=2 node=0 flags=0x0 nice=0 active=1/1 > > [ 273.416415] pending: xfs_buf_ioend_work [xfs] > > > > ... which suggests that it was queued..? I suppose this could be one of > > the workqueues waiting on a kthread, but xfs-buf also has a rescuer that > > appears to be idle: > > > > [ 1041.555227] xfs-buf/sda1 S14904 450 2 0x00000000 > > [ 1041.556813] Call Trace: > > [ 1041.557796] __schedule+0x336/0xe00 > > [ 1041.558983] schedule+0x3d/0x90 > > [ 1041.560085] rescuer_thread+0x322/0x3d0 > > [ 1041.561333] kthread+0x10f/0x150 > > [ 1041.562464] ? worker_thread+0x4b0/0x4b0 > > [ 1041.563732] ? kthread_create_on_node+0x70/0x70 > > [ 1041.565123] ret_from_fork+0x31/0x40 > > > > So shouldn't that thread pick up the work item if that is the case? > > Is it possible that the progress is done but tediously slow? Keep in > mind that the test case is doing write from 1k processes while one > process basically consumes all the memory. So I wouldn't be surprised > if this just made system to crawl on any attempt to do an IO. That would seem like a possibility to me.. either waiting on an actual I/O (no guarantee that the pending xfs-buf item is the one we care about I suppose) completion or waiting for whatever needs to happen for the wq infrastructure to kick off the rescuer. Though I think that's probably something Tetsuo would ultimately have to confirm on his setup.. Brian > -- > Michal Hocko > SUSE Labs > -- > To unsubscribe from this list: send the line "unsubscribe linux-xfs" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
