On Wed 16-12-15 15:58:44, Andrew Morton wrote: > 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? This is the time until the oom situation settled down. And I really suspect that the new SSD made a difference here. > 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. Which is what I was looking at when checking the timestamp in the log. [...] > > * 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. Yes, this is really hard to tell. What I wanted to achieve here is a determinism - the same load should give comparable results. It seems that there is an improvement in this regards. The time to settle is much more consistent than with the original implementation. > > 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. Well, I had to tune the test to see how close to the edge I can get. I haven't done any decisions based on this test. Thanks! -- Michal Hocko 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>