Igniters, What is being suggested here is an Ignite off-heap’s version of Java’s -XX:+AlwaysPreTouch. The latter is known to be used to guarantee that the committed memory is backed by physical RAM. This ensures that a) JVM doesn’t have to do it during the actual work (avoiding overhead for physical page allocation, possible contention with page cache, etc) b) JVM fails fast if the Xmx is greater than available RAM c) New processes will not be able to claim the memory JVM took for itself
Currently one can’t get the same benefits for Ignite because we use off-heap as well as heap. So, we can implement a similar feature for Ignite – and make sure the users can get all the memory pre-touch benefits if they want. Of course, it impacts startup time so we should enable it by a configuration property (I’d suggest a system property for now). Are there any objections to implementing this? Thanks, Stan From: Павлухин Иван Sent: 31 октября 2018 г. 12:50 To: dev@ignite.apache.org Subject: Re: Pre-touch for Ignite off-heap memory Hi, I did an experiment described above. I created a patch with pre-touch [1] and started a JVM with an option -XX:+AlwaysPreTouch and configured Ignite with equal values for initial and max sizes for each data region. I did several runs. I observed JVM crash dumps [2], [3]. Also it is easy to observe JVM OOM-killed. [1] https://github.com/apache/ignite/pull/5220 [2] https://gist.github.com/pavlukhin/e5e6605e9b43666266667ba8d1aab42f#file-hs_err_pid5763-log [3] https://gist.github.com/pavlukhin/e5e6605e9b43666266667ba8d1aab42f#file-hs_err_pid6411-log вт, 30 окт. 2018 г. в 9:19, Павлухин Иван <vololo...@gmail.com>: > Hi guys, > > I am not aware that it is possible to run JVM in "allocation-free" fashion. > If you know that it is possible please share it. As I know JVM allocates > memory out of garbage collectable area for internal purposes like JIT, > GC itself. Also native built-it code can request memory allocation from OS, > e.g. zip facilities. If we imagine that system is running under memory > allocation > which is close to a limit then even small allocation request can fail and > lead > to OOM killing. > > But I think that a simple and useful thing that could be done first is > making > an experiment. As Andrey mentioned > > AFAIK, Ignite always pre-touch first region. So, you can try to set > region > > MAX size equal to MIN and get region allocated on node start. > If it is so then it should not be hard to launch Ignite and observe it > running > very close to OS memory limit with Java heap and Ignite off-heap > pre-touched. > After that one could check whether it is possible to observe Ignite OOM > killed. > Let's say my bet is that it is relatively easy to catch OOM here. > > What do you think? > > пт, 26 окт. 2018 г. в 18:18, Yakov Zhdanov <yzhda...@apache.org>: > >> Andrey, >> >> Probability of a OOM kill will be much lower if offheap is pretouched. >> What >> do you mean by JVM internal needs? In my understanding if user enables >> option to pretouch heap and fixes the heap to prevent jvm releasing memory >> back to OS, then OOM killing is very unlikely. >> >> I would agree that pretouch for offheap may be helpful in many cases. >> >> --Yakov >> > > > -- > Best regards, > Ivan Pavlukhin > -- Best regards, Ivan Pavlukhin
