Hi Stan, As I participated in discussion in current thread I would like to leave a comment.
Your concerns looks clear for me and if you believe that pre-touch will help product users then I have nothing against it. ср, 12 дек. 2018 г. в 11:09, Nikolay Izhikov <nizhi...@apache.org>: > > Hello, Stanislav. > > As far as I can see, we have controversal ticket based on previous dev-list > discussion: > > IGNITE-9113 - Allocate memory for a data region when first cache assigned to > this region is created [1] > > I planned to implement it soon. > Looks like we should have several options of memory(data regions) allocation: > > - allocate all on startup (AFAIK this is how current implementation > behave) > - allocate all on startup AND pre touch. > - allocate specific data region for first assignment. > - allocate specific data region for first assignment AND pre touch. > > What do you think? > > [1] https://issues.apache.org/jira/browse/IGNITE-9113 > > В Вт, 11/12/2018 в 19:39 +0300, Stanislav Lukyanov пишет: > > 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
