RFR: JDK-8232069: Enable CDS even when UseCompressedClassPointers and/or UseCompressedOops are false

[Yumin Qi]

Hi, Ioi


   Thanks for the review. See answers embedded.

    New URL: http://cr.openjdk.java.net/~minqi/8232069/webrev-01/

On 2/5/20 10:34 AM, Ioi Lam wrote:
> Hi Yumin,
>
>
> Looks good. Some nitpicks on the tests:
>
> CommandLineFlagComboNegative.java: the following line is not needed.
>
> import jdk.test.lib.cds.CDSTestUtils.Result;
>
Removed.
>
> TestCombinedCompressedFlags.java: DUMP_NORMAL_MSG doesn't seem to be 
> used by the test.
>
Removed.

Also changed to use TestCommon.dump/TestCommon.exec which better to 
check dum/run results.

> DifferentHeapSizes.java: after your change, 
> CDSTestUtils.MSG_COMPRESSION_MUST_BE_USED is no longer used anywhere 
> in the tests. Also, This message is no longer printed by the VM. I 
> think the CDSTestUtils.MSG_COMPRESSION_MUST_BE_USED field should be 
> removed.
>
>
Removed.
> IncompatibleOptions.java: COOPS_DUMP_WARNING can be removed.
>
Removed.
> The check_shared parameter for testExec() should be removed. It's 
> currently used only when expectedToFail == false. However, in all the 
> cases where expectedToFail == false, check_shared is always true.
>
>
Removed.

> Also, in filemap.cpp, before checking "compressed_oops() != 
> UseCompressedOops ...", I think it will be good to add a log to print 
> out the expected compressed mode. That way if the user gets an error, 
> they can run with -Xlog:cds to find out exactly what the reason is. E.g.
>
>     log_info(cds)("Archive was created with UseCompressedOops = %d, 
> UseCompressedClassPointers = %d",
>                           compressed_oops(), 
> compressed_class_pointers());
>     if (compressed_oops() != UseCompressedOops ...
>
Added.


Thanks

Yumin

>
> On 2/4/20 6:01 PM, Yumin Qi wrote:
>> Hi,
>>
>>    Please review fix:
>>
>>    Bug: https://bugs.openjdk.java.net/browse/JDK-8232069
>>
>>    Webrev:http://cr.openjdk.java.net/~minqi/8232069/webrev/
>>
>>     Description: Currently CDS only works when using compressed Oops 
>> turned on, -XX:+UseCompressedOops (default), the fix is allowing CDS 
>> works with uncompressed oops and uncompressed class pointers. The 
>> contents of InstanceKlass::_fields are depending on UseCompressedOops 
>> and UseCompressedClassPointers on/off. There are three suggestions as 
>> described in bug description:
>>
>> 1. Remember the compression mode at CDS dump time. At runtime, 
>> disable CDS if the compression mode is changed.
>> 2. Same as 1, but save more than one CDS archives in the JDK image. 
>> Choose the appropriate one at start-up
>> 3. Recompute re-compute InstanceKlass::_fields at runtime.
>>
>> The fix takes the first one, storing UseCompressedOops and 
>> UseCompressedClassPointers in shared archive. CDS is only allowed at 
>> runtime if the flags are consistent with the stored versions in archive.
>>
>>  Testing: hs-tier1-2
>>
>>
>>   Thanks
>>
>>   Yumin
>>
>