RFR(XS): 8240691: serviceability/sa/ClhsdbCDSJstackPrintAll.java and serviceability/sa/ClhsdbCDSCore.java not work with ZGC

[Ioi Lam]

On 3/10/20 10:26 AM, Chris Plummer wrote:
> Ok, that makes sense. I committed a change recently that issues an 
> "echo true" command so all commands that follow are echoed, which is 
> why you now see "verbose true" in the output. So this resulted in it 
> always thinking that shared spaces was enabled, even when not. But 
> this did not cause any difference in behavior I think because of 
> JDK-8240698 (I'm still not real clear on that).
>
> And after fixing this issue and JDK-8240698 we will then start to see 
> issues because ZGC does not support SA, and therefore need a 3rd bug 
> to fix that?
>

Hi Chris,


I think we need to fix things in the following order. The goal is to 
increase test coverage for CDS.



[1] 8240691 - (I renamed the bug to) "ClhsdbCDSJstackPrintAll 
incorrectly thinks CDS is in use")

After the above is fixed, we still won't run ClhsdbCDSJstackPrintAll for 
jtreg -vmoption:-XX:+UseZGC yet, because this test has "@requires 
vm.cds", which reports false when ZGC is selected.



[2] 8240563 - WB_IsCDSIncludedInVmBuild should support uncompressed 
oops/klasses

After the above is fixed, we can run a lot of *other* CDS tests with 
CDS+ZGC.

However, for ClhsdbCDSJstackPrintAll, when jtreg -vmoption:-XX:+UseZGC 
is used

+ the test dumps a CDS archive with ZGC enabled (use compressed oops = 
false)

+ the test tries to use the CDS archive without enabling ZGC (due to 
8240698), so compressed oops = true. As a result, the VM cannot load 
this CDS archive because the oop compression mode doesn't match.



[3] 8240698 - LingeredApp did not pass getTestJavaOpts() to the children 
process if vmArguments is already specified

After the above is fixed, ClhsdbCDSJstackPrintAll will dump and run with 
the archive with -XX+UseZGC, so we can test the behavior of SA when ZGC 
is enabled.



But as Chris said, SA doesn't support ZGC yet (JDK-8220624), so we 
probably don't need to fix 8240698 until SA supports ZGC. As a 
precaution, we should disable this test in ProblemList-zgc.txt as a part 
of 8240563.

Also, I think the behavior of 8240698 may be intentional -- in many 
cases, especially when with "jtreg -vmoption:-Xcomp", you probably don't 
want the LingerApp to run with -Xcomp. So we should have an API in 
LingerApp.startApp() to explicitly allow the passing of 
getTestJavaOpts() to the child process.

Thanks
- Ioi


> Chris
>
> On 3/10/20 9:38 AM, Ioi Lam wrote:
>> Hi Chris,
>>
>>
>> The test uses this to check if CDS is on:
>>
>>     List<String> cmds = List.of("flags UseSharedSpaces");
>>     String useSharedSpacesOutput = test.run(theApp.getPid(), cmds,
>>                                                     null, null);
>>     ....
>>     if (!useSharedSpacesOutput.contains("true")) {
>>         // CDS archive is not mapped. Skip the rest of the test.
>>
>> The output looks like this:
>>
>>     hsdb> hsdb> + verbose true
>>     hsdb> + flags UseSharedSpaces
>>     UseSharedSpaces = false command line
>>     hsdb> + quit
>>
>> I think at one point the "if" worked, but the "+ verbose true" part 
>> of the log must have been added recently to cause the "if" to 
>> determine the wrong result.
>>
>> Thanks
>> - Ioi
>>
>>
>>
>> On 3/9/20 9:33 PM, Chris Plummer wrote:
>>> Hi Yumin,
>>>
>>> While your fix is a more bullet proof way of checking if CDS is on, 
>>> what was broken with the original version (was there a stray "false" 
>>> in the output"), and what does this have to do with ZGC?
>>>
>>> thanks,
>>>
>>> Chris
>>>
>>> On 3/9/20 8:06 PM, Yumin Qi wrote:
>>>>
>>>> Hi,
>>>>
>>>>     I made a change after discussed with Ioi, the test should check 
>>>> against UseSharedSpaces instead, it passed with/without change of 
>>>> 8240563 (tested in local). Also passed tier1,2,3.
>>>>
>>>>      URL: http://cr.openjdk.java.net/~minqi/8240691/webrev/
>>>>
>>>>
>>>>     Thanks
>>>>
>>>>      Yumin
>>>>
>>>>
>>>> On 3/6/20 2:26 PM, Yumin Qi wrote:
>>>>> HI,
>>>>>
>>>>>   Can I have your reviews on
>>>>>
>>>>>   Bug: https://bugs.openjdk.java.net/browse/JDK-8240691
>>>>>
>>>>>   webrev: http://cr.openjdk.java.net/~minqi/8240691/webrev/
>>>>>
>>>>>   Summary: With JDK-8232069 
>>>>> (https://bugs.openjdk.java.net/browse/JDK-8232069), CDS works with 
>>>>> UseCompressedOop and UseCompressedClassPointers off. The code for 
>>>>> detecting CDS will report false with ZGC since ZGC turned off 
>>>>> those two flags. The detection code will be changed in 
>>>>> JDK-8240563(https://bugs.openjdk.java.net/browse/JDK-8240563), 
>>>>> this will cause those two tests fail.
>>>>>
>>>>>
>>>>>    Tests: jtreg to show the tests not selected with ZGC.
>>>>>
>>>>>    Thanks
>>>>>
>>>>>    Yumin
>>>>>
>>>
>>
>