RFR (S) 8024517: runtime/CDSCompressedKPtrs/XShareAuto.java failed with RuntimeException

[harold seigel]

Hi David,

Thanks for the review.  Without the conditional compilation flags around 
the definition of no_shared_spaces(), I was getting a "defined but not 
used" error when building client.

Thanks, Harold

On 9/19/2013 1:35 AM, David Holmes wrote:
> Hi Harold,
>
> On 18/09/2013 11:15 AM, harold seigel wrote:
>> Hi,
>>
>> Please review this updated webrev for bug 8024517:
>> http://cr.openjdk.java.net/~hseigel/bug_8024517.2/
>> <http://cr.openjdk.java.net/%7Ehseigel/bug_8024517.2/>
>>
>> The updates are based on comments from Coleen and David.  CDS will be
>> off by default when -server is specified and on by default for -client.
>
> Ok.
>
>> Also, conditional compilation flags were put around function
>> no_shared_spaces() in arguments.cpp to fix a compilation problem when
>> building -client.
>
> Ok. Did you get an "unused" warning?
>
>> The ObjectAlignmentInBytes reference was removed from the test along
>> with the 64-bit requirement.
>
> Ok.
>
> However, note that just because you pass -server it doesn't mean the 
> server VM will run. The jvm.cfg file can, and does, alias server to 
> client. We don't have a general solution to this problem at the moment.
>
> David
> -----
>
>
>
>> Thanks, Harold
>>
>> On 9/17/2013 3:22 PM, Coleen Phillimore wrote:
>>>
>>> Hi David,
>>>
>>> On 09/16/2013 11:40 PM, David Holmes wrote:
>>>> On 17/09/2013 12:53 AM, harold seigel wrote:
>>>>> Hi David,
>>>>>
>>>>> Thanks for the review.
>>>>
>>>> Only "attempted review" at that stage :)
>>>>
>>>>> My proposed fix maintains the current behavior for the client VM, 
>>>>> which
>>>>> is that CDS is off by default if running on a server class machine.
>>>>> (Fwiw: the test for server class machine
>>>>> (os::is_server_class_machine())
>>>>> usually returns FALSE for c1 because NeverActAsServerClassMachine
>>>>> defaults to TRUE for c1 for arm, x86, ppc, and Sparc.)
>>>>>
>>>>> The fix only changes the behavior for -server. Previously, CDS was 
>>>>> off
>>>>> by default for -server only if the JVM was running on a server class
>>>>> machine.  With this change, CDS will always be off by default when
>>>>> -server is specified.  The fix implements this change by no longer
>>>>> checking for a  server class machine when running the server VM.
>>>>
>>>> Okay I think I have it now. This all seems rather convoluted - not
>>>> sure why we care about server-class-machine to make a CDS choice?
>>>
>>> We don't care about server class machine.  We want to turn CDS off by
>>> default for -server because it degrades performance.  This
>>> server-class-machine means -server almost all of the time but in this
>>> corner case didn't mean -server.   So the gist of Harold's change is
>>> to turn it off for -server, which we want.
>>>
>>> Looking at Harold's change, we should just turn off CDS by default
>>> (ie. unless specified) under #ifdef COMPILER2 and not check for server
>>> class machine for the client compiler.
>>>
>>>>
>>>>
>>>> That aside what do we document about the CDS behaviour? Does this
>>>> change need CCC request and/or updates to docs?
>>>
>>> I think it's not an interesting corner case and not really intended as
>>> a change in behavior.  It's what we assumed it was doing in the first
>>> place.
>>>
>>> I can't comment on the test right now.
>>>
>>> Coleen
>>>>
>>>>> The test failure reported in the bug occurred because the test was 
>>>>> run
>>>>> with -server on a non server class machine and CDS was not 
>>>>> disabled as
>>>>> expected.
>>>>
>>>> Ok. Not sure why the test is 64-bit only though and why does it refer
>>>> to ObjectAlignmentInBytes? Is this a copy/n/paste error when the test
>>>> was created? I see this under the "compressed Kptrs" which is
>>>> presumably 64-bit only, but the tests doesn't see 64-bit related ??
>>>>
>>>> Thanks,
>>>> David
>>>>
>>>>> Thanks, Harold
>>>>>
>>>>> On 9/14/2013 3:41 AM, David Holmes wrote:
>>>>>> Hi Harold,
>>>>>>
>>>>>> Sorry I am a bit confused about the problem and solution. CDS should
>>>>>> be off when using the server VM - right? But this code:
>>>>>>
>>>>>> ! #ifndef COMPILER2
>>>>>> !   if (is_server_class_mach)
>>>>>> ! #endif
>>>>>>
>>>>>> only affects the client VM, so you seem to be saying that CDS should
>>>>>> be off on a client VM when running on a server class machine ???
>>>>>>
>>>>>> David
>>>>>>
>>>>>> On 14/09/2013 5:05 AM, harold seigel wrote:
>>>>>>> Hi,
>>>>>>>
>>>>>>> Please review this small fix for bug 8024517.  This test failed
>>>>>>> when run
>>>>>>> on a small system because CDS was not disabled by default.
>>>>>>> Although the
>>>>>>> test was run with '-server', CDS was not disabled because function
>>>>>>> os::is_server_class_machine() returned FALSE.  This fix disables
>>>>>>> CDS by
>>>>>>> default if either os::is_server_class_machine() returns TRUE or the
>>>>>>> server compiler is running.
>>>>>>>
>>>>>>> Also, the '-server' option was added to the test's '-Xshare:dump'
>>>>>>> command to ensure that the CDS region gets created by the same JVM
>>>>>>> that
>>>>>>> tries to read it.
>>>>>>>
>>>>>>> The change was tested with the XShareAuto.java test, by hand using
>>>>>>> the
>>>>>>> NeverActAsServerClassMachine and AlwaysActAsServerClassMachine
>>>>>>> options,
>>>>>>> the UTE vm quicktests, and JPRT.
>>>>>>>
>>>>>>> Open webrev at: http://cr.openjdk.java.net/~hseigel/bug_8024517/
>>>>>>> <http://cr.openjdk.java.net/%7Ehseigel/bug_8024517/>
>>>>>>> Bug: https://bugs.openjdk.java.net/browse/JDK-8024517
>>>>>>>
>>>>>>> Thanks! Harold
>>>>>
>>>
>>