On Tue, 15 Dec 2015 19:19:43 +0100 Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > ... > > * base kernel > $ grep "Killed process" base-oom-run1.log | tail -n1 > [ 211.824379] Killed process 3086 (mem_eater) total-vm:85852kB, anon-rss:81996kB, file-rss:332kB, shmem-rss:0kB > $ grep "Killed process" base-oom-run2.log | tail -n1 > [ 157.188326] Killed process 3094 (mem_eater) total-vm:85852kB, anon-rss:81996kB, file-rss:368kB, shmem-rss:0kB > > $ grep "invoked oom-killer" base-oom-run1.log | wc -l > 78 > $ grep "invoked oom-killer" base-oom-run2.log | wc -l > 76 > > The number of OOM invocations is consistent with my last measurements > but the runtime is way too different (it took 800+s). I'm seeing 211 seconds vs 157 seconds? If so, that's not toooo bad. I assume the 800+s is sum-across-multiple-CPUs? Given that all the CPUs are pounding away at the same data and the same disk, that doesn't sound like very interesting info - the overall elapsed time is the thing to look at in this case. > One thing that > could have skewed results was that I was tail -f the serial log on the > host system to see the progress. I have stopped doing that. The results > are more consistent now but still too different from the last time. > This is really weird so I've retested with the last 4.2 mmotm again and > I am getting consistent ~220s which is really close to the above. If I > apply the WQ vmstat patch on top I am getting close to 160s so the stale > vmstat counters made a difference which is to be expected. I have a new > SSD in my laptop which migh have made a difference but I wouldn't expect > it to be that large. > > $ grep "DMA32.*all_unreclaimable? no" base-oom-run1.log | wc -l > 4 > $ grep "DMA32.*all_unreclaimable? no" base-oom-run2.log | wc -l > 1 > > * patched kernel > $ grep "Killed process" patched-oom-run1.log | tail -n1 > [ 341.164930] Killed process 3099 (mem_eater) total-vm:85852kB, anon-rss:82000kB, file-rss:336kB, shmem-rss:0kB > $ grep "Killed process" patched-oom-run2.log | tail -n1 > [ 349.111539] Killed process 3082 (mem_eater) total-vm:85852kB, anon-rss:81996kB, file-rss:4kB, shmem-rss:0kB Even better. > $ grep "invoked oom-killer" patched-oom-run1.log | wc -l > 78 > $ grep "invoked oom-killer" patched-oom-run2.log | wc -l > 77 > > $ grep "DMA32.*all_unreclaimable? no" patched-oom-run1.log | wc -l > 1 > $ grep "DMA32.*all_unreclaimable? no" patched-oom-run2.log | wc -l > 0 > > So the number of OOM killer invocation is the same but the overall > runtime of the test was much longer with the patched kernel. This can be > attributed to more retries in general. The results from the base kernel > are quite inconsitent and I think that consistency is better here. It's hard to say how long declaration of oom should take. Correctness comes first. But what is "correct"? oom isn't a binary condition - there's a chance that if we keep churning away for another 5 minutes we'll be able to satisfy this allocation (but probably not the next one). There are tradeoffs between promptness-of-declaring-oom and exhaustiveness-in-avoiding-it. > > 2) 2 writers again with 10s of run and then 10 mem_eaters to consume as much > memory as possible without triggering the OOM killer. This required a lot > of tuning but I've considered 3 consecutive runs without OOM as a success. "a lot of tuning" sounds bad. It means that the tuning settings you have now for a particular workload on a particular machine will be wrong for other workloads and machines. uh-oh. > ... -- 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>