RFR (L) 8072061: Automatically determine optimal sizes for the CDS regions

[coleen.phillimore at oracle.com]

Ioi, I have one comment and one question.

http://cr.openjdk.java.net/~iklam/jdk10/8072061-auto-size-cds-region.v10/hotspot/src/share/vm/memory/metaspace.cpp.udiff.html

This cleanup is worth all of the change.   It's nice to not conflate 
metaspace allocation with the creating shared region anymore.   It 
started out as a little bit of extra code but has expanded to all of 
what you removed.   So I guess you've convinced me that copying metadata 
is worth doing.

http://cr.openjdk.java.net/~iklam/jdk10/8072061-auto-size-cds-region.v10/hotspot/src/share/vm/utilities/hashtable.cpp.udiff.html

Why do you have to include metaspaceShared.hpp here?

I've prereviewed this and have no further comments.   This looks good!  
Thank you for making the changes I suggested in the pre-review.  
Starting with copy_and_compact() it makes sense what this is doing and 
looks like it'll be easier to understand overall.

Thanks!
Coleen


On 6/29/17 6:55 PM, Ioi Lam wrote:
> https://bugs.openjdk.java.net/browse/JDK-8072061
> http://cr.openjdk.java.net/~iklam/jdk10/8072061-auto-size-cds-region.v10/
>
> ------------------------------------------------------------------------------ 
>
> Motivation:
>
>   The CDS archive is divided in several regions such as RO, RW, etc. In
>   JDK 9, when you are dumping with a custom classlist, you must manually
>   specify the region sizes using flags such as -XX:SharedReadOnlySize.
>   This is error prone and cumbersome.
>
>   This RFE makes it possible to automatically determine the optimal sizes
>   of the regions.
>
> Overview:
>
>   With this RFE, during CDS dump time, all class metadata are first
>   allocated outside of the shared regions. Then, we scan all of the
>   reachable metadata objects, determine whether they are RO or RW, and
>   then copy them into the destination regions.
>
>   After all objects are copied, we scan and relocate all the pointers to
>   point to the new copies.
>
> Notes to reviewers:
>
>   To implement the copy and relocation operations, we have added the new
>   MetaspaceClosure API for walking all the reachablemetadata objects, and
>   scanning all the pointers embedded in these objects.
>
>   Please start in metaspaceShared.cppand follow the code path:
>
>     ArchiveCompactor::copy_and_compact()
>     -> iterate_roots()
>       -> SystemDictionary::classes_do(it)
>         -> Dictionary::classes_do(MetaspaceClosure* it)
> -> it->push(probe->klass_addr())
>
>   At this point you will get into metaspaceClosure.hpp. Please read the
>   comments around MetaspaceClosure::Ref about the (lack of) C++ vtables,
>   and why the template classes ObjectRef, PrimitiveArrayRef and
>   PointerArrayRef are needed.
>
>   Once you understand how ObjectRefand PointerArrayRef work, you can
>   see that the above it->push(probe->klass_addr()) call will be invoking
>   this template method:
>
>      template <class T> void push(T** mpp, Writability w = _default) {
>        ObjectRef<T> ref(mpp);
>        push_impl(&ref, w);
>      }
>
>   which will eventually call into Klass::metaspace_pointers_do(), which
>   will eventually recursively iterate over all the Klasses, Methods,
>   ConstantPools and other types of MetaspaceObj.
>
> Testingstatus:
>
>   All CDS tests have passed locally on Linux. All new tests have been
> implemented.
>
> I am waiting to run RBT tests on other platforms.
>
> Thanks
> - Ioi