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

Volker Simonis volker.simonis at gmail.com
Mon Jun 18 16:04:58 UTC 2018

On Mon, Jun 18, 2018 at 8:17 AM, David Holmes <david.holmes at oracle.com> wrote:
> 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!)

Yes, you're right, CDS_ONLY/NOT_CDS isn't really required here,
because UseSharedSpaces is reseted later on at the end of
Arguments::parse(). I just thought it would be cleaner to disable it
statically, if the VM doesn't support it. But anyway I don't really
mind and I've reverted that change in globals.hpp.

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

Thomas and you are right. Must have been a mis-configuration on AIX
where I saw undefined symbols at link time. I've removed the ifdefs
from javaClasses.cpp now.

Finally, I've also wrapped all the FileMapInfo fields in vmStructs.cpp
into CDS_ONLY macros as suggested by Jiangli because the really only
make sense for a CDS-enabled VM.

Here's the new webrev:


Please let me know if you think there's still something missing.


> ??
> Thanks,
> David
> -----
> 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.

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