On Thu, Dec 29, 2016 at 03:26:15PM +1000, Nicholas Piggin wrote: > > And I fixed that too. > > > > Of course, I didn't test the changes (apart from building it). But > > I've been running the previous version since yesterday, so far no > > issues. > > It looks good to me. > FWIW, I blindly queued a test of Nick's patch, Linus' patch on top and PeterZ's patch using 4.9 as a baseline so all could be applied cleanly. 3 machines were used, one one of them NUMA with 2 sockets. The UMA machines showed nothing unusual. kernel building showed nothing unusual on any machine git checkout in a loop showed; o minor gains with Nick's patch o no impact from Linus's patch o flat performance from PeterZ's git test suite showed o close to flat performance on all patches o Linus' patch on top showed increased variability but not serious will-it-scale pagefault tests o page_fault1 and page_fault2 showed no differences in processes o page_fault3 using processes did show some large losses at some process counts on all patches. The losses were not consistent on each run. There also was no consistently at loss with increasing process counts. It did appear that Peter's patch had fewer problems with only one thread count showing problems so it *may* be more resistent to the problem but not completely and it's not obvious why it might be so it could be a testing anomaly o page_fault3 using threads didn't show anything unusual. It's possible that any problem with the waitqueue lookups is hidden by mmap_sem I think I can see something similar to Dave but not consistently and not as severe and only using processes for page_fault3. Linus's patch appears to help a little but not eliminate the problem. Given the machine only had 2 sockets, it's prefectly possible that Dave can see a consistent problem that I cannot. During the test run, I hadn't collected the profiles to see what is going on as the test queueing was a drive-by bit of work while on holiday. Reading both Nick's (which is already merged so somewhat moot) and PeterZ's patch, I did find Nick's easier to understand with some minor gripes about naming. None of the patches showed the same lost wakeup I'd seen once on earlier prototypes. -- Mel Gorman SUSE Labs -- 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>