On Wed, 14 Oct 2015, PINTU KUMAR wrote: > For me it was very helpful during sluggish and long duration ageing tests. > With this, I don't have to look into the logs manually. > I just monitor this count in a script. > The moment I get nr_oom_victims > 1, I know that kernel OOM would have happened > and I need to take the log dump. > So, then I do: dmesg >> oom_logs.txt > Or, even stop the tests for further tuning. > I think eventfd(2) was created for that purpose, to avoid the constant polling that you would have to do to check nr_oom_victims and then take a snapshot. > > I disagree with this one, because we can encounter oom kills due to > > fragmentation rather than low memory conditions for high-order allocations. > > The amount of free memory may be substantially higher than all zone > > watermarks. > > > AFAIK, kernel oom happens only for lower-order (PAGE_ALLOC_COSTLY_ORDER). > For higher-order we get page allocation failure. > Order-3 is included. I've seen machines with _gigabytes_ of free memory in ZONE_NORMAL on a node and have an order-3 page allocation failure that called the oom killer. > > We've long had a desire to have a better oom reporting mechanism rather than > > just the kernel log. It seems like you're feeling the same pain. I think it > would be > > better to have an eventfd notifier for system oom conditions so we can track > > kernel oom kills (and conditions) in userspace. I have a patch for that, and > it > > works quite well when userspace is mlocked with a buffer in memory. > > > Ok, this would be interesting. > Can you point me to the patches? > I will quickly check if it is useful for us. > https://lwn.net/Articles/589404. It's invasive and isn't upstream. I would like to restructure that patchset to avoid the memcg trickery and allow for a root-only eventfd(2) notification through procfs on system oom. -- 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>