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

[Thomas Stüfe]

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