code review request for MacOS X compressed oops work around (7118648)

[Vladimir Kozlov]

Daniel D. Daugherty wrote:
> David,
> 
> Thanks for the quick review!
> 
> On 12/6/11 11:08 PM, David Holmes wrote:
>> On 7/12/2011 2:51 PM, Vladimir Kozlov wrote:
>>> Could you move the comment before #ifndef __APPLE__?
>>
>> I second that.
> 
> Will move the comment.
> 
> 
>> If you didn't want the flag turned on at all you could use the 
>> UNSUPPORTED_OPTION macro.
> 
> Just wanted it false by default. If I disable it entirely, then
> it will be (slightly) harder to diagnose via 7118647...

Yes, we need to turn on COOP on command line to debug the probem. This fix is good.

Thanks,
Vladimir

> 
> Dan
> 
> 
>>
>> David
>>
>>> Vladimir
>>>
>>> Daniel D. Daugherty wrote:
>>>> Greetings,
>>>>
>>>> The UseCompressedOops flag is enabled ergonomically in a 64-bit VM.
>>>> With MacOS X, we're seeing intermittent crashes in our automated
>>>> build/test system (JPRT) that look like this:
>>>>
>>>> Internal Error
>>>> (/private/tmp/jprt/P1/050642.jmelvin/source/src/share/vm/runtime/virtualspace.cpp:460), 
>>>>
>>>> pid=53634, tid=4531154944
>>>> # assert((_noaccess_prefix != 0) == (UseCompressedOops && _base !=
>>>> NULL && (size_t(_base + _size) > OopEncodingHeapMax) &&
>>>> Universe::narrow_oop_use_implicit_null_checks())) failed:
>>>> noaccess_prefix should be used only with non zero based compressed oops
>>>>
>>>> I have filed the following bug to track that failure mode:
>>>>
>>>> 7118647 3/3 compressed oops crashes on MacOS X with JPRT GCBasher test
>>>>
>>>> In order to make more reliable progress on getting MacOS X fully
>>>> enabled in JPRT, I'm planning to disable compressed oops by default
>>>> in the 64-bit MacOS X VM until 7118647 can be fixed.
>>>>
>>>> The work around is trivial so I'm including it here rather than
>>>> generate a webrev:
>>>>
>>>> diff -r a5a9db0e0203 src/share/vm/runtime/arguments.cpp
>>>> --- a/src/share/vm/runtime/arguments.cpp Tue Dec 06 07:23:42 2011 -0800
>>>> +++ b/src/share/vm/runtime/arguments.cpp Tue Dec 06 15:29:17 2011 -0800
>>>> @@ -1359,9 +1359,12 @@
>>>> // by ergonomics.
>>>> if (MaxHeapSize <= max_heap_for_compressed_oops()) {
>>>> #if !defined(COMPILER1) || defined(TIERED)
>>>> +#ifndef __APPLE__
>>>> + // disable UseCompressedOops by default on MacOS X until 7118647 is
>>>> fixed
>>>> if (FLAG_IS_DEFAULT(UseCompressedOops)) {
>>>> FLAG_SET_ERGO(bool, UseCompressedOops, true);
>>>> }
>>>> +#endif // !__APPLE__
>>>> #endif
>>>> #ifdef _WIN64
>>>> if (UseLargePages && UseCompressedOops) {
>>>>
>>>>
>>>> What the above code does is prevent the UseCompressedOops flag
>>>> from being set to true ergonomically on MacOS X. It can still be
>>>> set to true with the '-XX:+UseCompressedOops' option.
>>>>
>>>> I'm planning to push this fix to RT_Baseline for the HSX-23-B08
>>>> snapshot. Jim Melvin has already reviewed the fix so I just need
>>>> one more reviewer.
>>>>
>>>> Thanks, in advance, for any additional reviews.
>>>>
>>>> Dan
>>>>