On Wed, Aug 19, 2015 at 07:56:11AM +1000, Dave Chinner wrote: > On Tue, Aug 18, 2015 at 12:54:39PM -0700, Tejun Heo wrote: > > Hello, > > > > On Tue, Aug 18, 2015 at 10:47:18AM -0700, Tejun Heo wrote: > > > Hmm... the only possibility I can think of is tot_write_bandwidth > > > being zero when it shouldn't be. I've been staring at the code for a > > > while now but nothing rings a bell. Time for another debug patch, I > > > guess. > > > > So, I can now reproduce the bug (it takes a lot of trials but lowering > > the number of tested files helps quite a bit) and instrumented all the > > early exit paths w/o the fix patch. bdi_has_dirty_io() and > > wb_has_dirty_io() are never out of sync with the actual dirty / io > > lists even when the test 048 fails, so the bug at least is not caused > > by writeback skipping due to buggy bdi/wb_has_dirty_io() result. > > Whenever it skips, all the lists are actually empty (verified while > > holding list_lock). > > > > One suspicion I have is that this could be a subtle timing issue which > > is being exposed by the new short-cut path. Anything which adds delay > > seems to make the issue go away. Dave, does anything ring a bell? > > No, it doesn't. The data writeback mechanisms XFS uses are all > generic. It marks inodes I_DIRTY_PAGES and lets the generic code > take care of everything else. Yes, we do delayed allocation during > writeback, and we log the inode size updates during IO completion, > so if inode sizes are not getting updated, then Occam's Razor > suggests that writeback is not happening. > > I'd suggest looking at some of the XFS tracepoints during the test: > > tracepoint trigger > xfs_file_buffered_write once per write syscall > xfs_file_sync once per fsync per inode > xfs_vm_writepage every ->writepage call > xfs_setfilesize every IO completion that updates inode size I gave the tracepoints a try, but my root fs is xfs so I got many noises. I'll try to install a new vm with ext4 as root fs. But I'm not sure if the new vm could reproduce the failure, will see. BTW, I guess xfs_vm_writepage should be xfs_writepage, and xfs_file_sync should be xfs_file_fsync? Thanks, Eryu -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
