RFR(M): 8204965: Fix '--disable-cds' and disable CDS on AIX by default

[David Holmes]

Hi Volker,

src/hotspot/share/runtime/globals.hpp

This change should not be needed! We do minimal VM builds without CDS 
and we don't have to touch the UseSharedSpaces defaults (unless recent 
change have broken this - in which case that needs to be addressed in 
its own right!)

src/hotspot/share/classfile/javaClasses.cpp

AFAICS you should be using INCLUDE_CDS in the ifdefs not 
INCLUDE_CDS_JAVA_HEAP. But again I'm unclear (as was Thomas) why this 
should be needed as we have not needed it before. As Thomas notes we have:

./hotspot/share/memory/metaspaceShared.hpp:  static bool 
is_archive_object(oop p) NOT_CDS_JAVA_HEAP_RETURN_(false);
./hotspot/share/classfile/stringTable.hpp:  static oop 
create_archived_string(oop s, Thread* THREAD) 
NOT_CDS_JAVA_HEAP_RETURN_(NULL);

so these methods should be defined when CDS is not available.

??

Thanks,
David
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On 15/06/2018 12:26 AM, Volker Simonis wrote:
> Hi,
> 
> can I please have a review for the following fix:
> 
> http://cr.openjdk.java.net/~simonis/webrevs/2018/8204965/
> https://bugs.openjdk.java.net/browse/JDK-8204965
> 
> CDS does currently not work on AIX because of the way how we
> reserve/commit memory on AIX. The problem is that we're using a
> combination of shmat/mmap depending on the page size and the size of
> the memory chunk to reserve. This makes it impossible to reliably
> reserve the memory for the CDS archive and later on map the various
> parts of the archive into these regions.
> 
> In order to fix this we would have to completely rework the memory
> reserve/commit/uncommit logic on AIX which is currently out of our
> scope because of resource limitations.
> 
> Unfortunately, I could not simply disable CDS in the configure step
> because some of the shared code apparently relies on parts of the CDS
> code which gets excluded from the build when CDS is disabled. So I
> also fixed the offending parts in hotspot and cleaned up the configure
> logic for CDS.
> 
> Thank you and best regards,
> Volker
> 
> PS: I did run the job through the submit forest
> (mach5-one-simonis-JDK-8204965-20180613-1946-26349) but the results
> weren't really useful because they mention build failures on linux-x64
> which I can't reproduce locally.
>