how to start with CRaC when enable jvm gc files.

[suixingbugai]

when enable gc files output，this error happens. how to start with CRaC when enable gc files.

[AntonKozlov]

Hi, JVM or JDK owned files should be coordinated with CRaC, so this should be considered as a bug. So thanks for the report!

So far, as the workaround, please try -XX:CRaCIgnoredFileDescriptors=/app/gc.log (although I have not tested this)

[suixingbugai]

@AntonKozlov when use -XX:+UseZGC，execute jcmd command throw exception like this picture.

[rvansa]

@suixingbugai This is a known issue; C/R is not handled in ZGC yet.

[suixingbugai]

@suixingbugai This is a known issue; C/R is not handled in ZGC yet.

When we will handle this C/R issue in ZGC ?

[rvansa]

While I personally consider ZGC to be a great GC, mainly for bigger heaps, it has not been prioritized yet (I guess that applications that need to start fast, e.g. quickly scaling microservices, usually use smaller heaps where G1 works well). But please let's not divert the discussion; this issue is about JVM not closing its logs on checkpoint. Feel free to create another issue for ZGC, especially if you're willing to work on that.

[suixingbugai]

While my team is using G1 in production stage without CRaC, it really works well now . But we are considering repleace G1 with ZGC for small stw times ，start with CRaC to start fast，it seems to be difficlut. Can you give me some suggestions?

[rvansa]

Suggestions for what, exactly? ZGC uses memory in an anonymous file. CRIU itself should be able to deal with that; you'd need to add an exception for this in VM_Crac::check_fds(). It's possible that more tweaks will be needed, though; e.g. it would be nice to zero any memory that's not used to minimize the size of checkpoint image.

[jankratochvil]

openjdk/crac#113 = CRaC: Fix fds opened for logging

[jankratochvil]

ZGC itself is still incompatible with CRaC but at least it now prints a better error message: https://github.com/openjdk/crac/pull/90/files
The opened log files should be fixed by: https://github.com/openjdk/crac/pull/113/files
Therefore could we close this issue?