RFR(xs): 8247252: TestCombinedCompressedFlags.java failed src/hotspot/share/services/virtualMemoryTracker.cpp:388 Error: ShouldNotReachHere()

[David Holmes]

Hi Thomas,

On 11/06/2020 4:50 pm, Thomas Stüfe wrote:
> May I have a second review please?

This all appears reasonable to me.

Nit:

test/hotspot/jtreg/runtime/cds/appcds/TestCombinedCompressedFlags.java

One arg per line please.

Thanks,
David

> Thanks!
> 
> ..Thomas
> 
> On Wed, Jun 10, 2020 at 3:09 PM Thomas Stüfe <thomas.stuefe at gmail.com>
> wrote:
> 
>> Hi all,
>>
>> could I please have reviews for this bug fix.
>>
>> JBS: https://bugs.openjdk.java.net/browse/JDK-8247252
>> webrev:
>> http://cr.openjdk.java.net/~stuefe/webrevs/8247252-cds-nmt-ccps-off/webrev.00/webrev/
>>
>> This bug was introduced with "8243535 NMT may show wrong numbers for CDS
>> and CCS".
>>
>> The error is that a VM loading a shared archive but having compressed
>> class pointers disabled would reserve space for the CDS but fail to
>> register it with the correct tag with NMT. So, inside NMT it still is
>> marked as "mtUnknown". This leads to a follow up error when the actual
>> archive files are to be mapped into this reserved region, since the region
>> is expected to carry the "mtClassShared" tag for this to work.
>>
>> The fix is simple to add the missing registration in metaspaceShared.cpp
>> when the cds has been reserved for the non-class-space case:
>>
>> @@ -2469,10 +2470,12 @@
>>       archive_space_rs = ReservedSpace(archive_space_size,
>> archive_space_alignment,
>>                                        false /* bool large */,
>> (char*)base_address);
>>       if (archive_space_rs.is_reserved()) {
>>         assert(base_address == NULL ||
>>                (address)archive_space_rs.base() == base_address, "Sanity");
>> +      // Register archive space with NMT.
>> +      MemTracker::record_virtual_memory_type(archive_space_rs.base(),
>> mtClassShared);
>>         return archive_space_rs.base();
>>       }
>>       return NULL;
>>     }
>>
>> All the rest is fluff:
>>
>> - added logging in a number of places to make analysis of these kinds of
>> errors simpler
>> - explicitly switched on NMT for a number of cds jtreg tests.
>>
>> ---
>>
>> The reason we did not see these errors before in our (SAPs) CI was that we
>> run our tests with NMT (by default) switched off. Apparently Oracle runs
>> the jtreg tests with NMT enabled via -vmoptions? We will change our CI to
>> do this too. But it would be good if the test flags would be published
>> somewhere, and we would all use the same flags.
>>
>> Thanks, Thomas
>>