On Mon, Jan 20, 2014 at 04:59:23PM -0800, Andy Lutomirski wrote: > The code below runs quickly for a few iterations, and then it slows > down and the whole system becomes laggy for far too long. > > Removing the sync_file_range call results in no I/O being performed at > all (which means that the kernel isn't totally screwing this up), and > changing "4096" to SIZE causes lots of I/O but without > the going-out-to-lunch bit (unsurprisingly). More details please. hardware, storage, kernel version, etc. I can't reproduce any slowdown with the code as posted on a VM running 3.31-rc5 with 16GB RAM and an SSD w/ ext4 or XFS. The workload is only generating about 80 IOPS on ext4 so even a slow spindle should be able handle this without problems... > Surprisingly, uncommenting the ftruncate call seems to fix the > problem. This suggests that all the necessary infrastructure to avoid > wasting time writing to deleted files is there but that it's not > getting used. Not surprising at all - if it's stuck in a writeback loop somewhere, truncating the file will terminate writeback because it end up being past EOF and so stops immediately... Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- 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>