Folks, I just booted up a 3.0-rc1 kernel, and mounted an XFS filesystem with 50M files in it. Running: $ for i in /mnt/scratch/*; do sudo /usr/bin/time rm -rf $i 2>&1 & done runs an 8-way parallel unlink on the files. Normally this runs at around 80k unlinks/s, and it runs with about 500k-1m dentries and inodes cached in the steady state. The steady state behaviour with 3.0-rc1 is that there are around 10m cached dentries - all negative dentries - consuming about 1.6GB of RAM (of 4GB total). Previous steady state was, IIRC, around 200MB of dentries. My initial suspicions are that the dentry unhashing changeÑ may be the cause of this... Performance is now a very regular peak/trough patten with a period of about 20s, where the peak is about 80k unlinks/s, and the trough is around 20k unlinks/s. The runtime of the 50m inode delete has gone from around 10m on 2.6.39, to: 11.71user 470.08system 15:07.91elapsed 53%CPU (0avgtext+0avgdata 133184maxresident)k 0inputs+0outputs (30major+497228minor)pagefaults 0swaps 11.50user 468.30system 15:14.35elapsed 52%CPU (0avgtext+0avgdata 133168maxresident)k 0inputs+0outputs (42major+497268minor)pagefaults 0swaps 11.34user 466.66system 15:26.04elapsed 51%CPU (0avgtext+0avgdata 133216maxresident)k 0inputs+0outputs (18major+497121minor)pagefaults 0swaps 12.14user 470.46system 15:26.60elapsed 52%CPU (0avgtext+0avgdata 133216maxresident)k 0inputs+0outputs (44major+497309minor)pagefaults 0swaps 12.06user 463.74system 15:28.84elapsed 51%CPU (0avgtext+0avgdata 133232maxresident)k 0inputs+0outputs (25major+497046minor)pagefaults 0swaps 11.37user 468.18system 15:29.07elapsed 51%CPU (0avgtext+0avgdata 133184maxresident)k 0inputs+0outputs (55major+497056minor)pagefaults 0swaps 11.69user 474.46system 15:47.45elapsed 51%CPU (0avgtext+0avgdata 133232maxresident)k 0inputs+0outputs (61major+497284minor)pagefaults 0swaps 11.32user 476.93system 16:05.14elapsed 50%CPU (0avgtext+0avgdata 133184maxresident)k 0inputs+0outputs (30major+497225minor)pagefaults 0swaps About 16 minutes. I'm not sure yet whether this change of cache behaviour is the cause of the entire performance regression, but it's a good chance that it is a contributing factor. Christoph, it appears that there is a significant increase in log forces during this unlink workload compared to 2.6.39, and that's possibly where the performance degradation is coming from. I'm going to have to bisect, I think. The 8-way create rate for the 50m inodes is down by 10% as well, but I don't think that has anything to do with dentry cache behaviour - log write throughput is up by a factor of 3x over 2.6.39. Christoph, I think that this is once again due to an increase in log forces, but I need to do more analysis to be sure... Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- 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
