8196989: Revamp G1 JMX MemoryPool and GarbageCollector MXBean definitions

Hohensee, Paul hohensee at amazon.com
Thu Oct 18 22:18:35 UTC 2018


Thanks for your review, JC.  New webrev: http://cr.openjdk.java.net/~phh/8196989/webrev.03/

I updated the copyright date in memoryService.hpp because I forgot to do so in the patch for https://bugs.openjdk.java.net/browse/JDK-8195115. Thomas asked me to fix in it a separate CR, so I’ve reverted it. Ditto the #include fixes in g1FullGCOopClosures.inline.hpp and g1HeapVerifier.cpp. At one point during development, clang complained about the latter, but no longer does.

The ‘break’ on the same line as the ‘}’ was in the original version, but I’ve moved it. :)

The comment is indeed a bit opaque. I changed it to:

        // Only check heap pools that support a usage threshold.
        // This is typically only the old generation space
        // since the other spaces are expected to get filled up.
        if (p.getType() == MemoryType.HEAP &&
           p.isUsageThresholdSupported()) {
               // In all collectors except G1, only the old generation supports a
                // usage threshold. The G1 legacy mode "G1 Old Gen" also does. In
                // G1 default mode, both the old space ("G1 Old Space": it's not
                // really a generation in the non-G1 collector sense) and the
                // humongous space ("G1 Humongous Space"), support a usage threshold.
                // So, the following condition is true for all non-G1 old generations,
                // for the G1 legacy old gen, and for the G1 default humongous space.
               // It is not true for the G1 default old gen.
                //
                // We're allocating humongous objects in this test, so the G1 default
                // mode "G1 Old Space" occupancy doesn't change, because humongous
                // objects are allocated in the "G1 Humongous Space". If we allowed
                // the G1 default mode "G1 Old Space", notification would never
                // happen because no objects are allocated there.
               if (!p.getName().equals("G1 Old Space")) {

Finally, the G1MonitoringScope constructor now does a better job of selecting a memory manager.

Paul

From: JC Beyler <jcbeyler at google.com>
Date: Wednesday, October 17, 2018 at 4:47 PM
To: "Hohensee, Paul" <hohensee at amazon.com>
Cc: "hotspot-gc-dev at openjdk.java.net" <hotspot-gc-dev at openjdk.java.net>, "serviceability-dev at openjdk.java.net" <serviceability-dev at openjdk.java.net>
Subject: Re: 8196989: Revamp G1 JMX MemoryPool and GarbageCollector MXBean definitions

Hi Paul,

I looked at this but it took time for me to "digest" it and I haven't entirely gone through the real GC changes :)

My few remarks on the webrev itself are:
   - http://cr.openjdk.java.net/~phh/8196989/webrev.02/src/hotspot/share/services/memoryService.hpp.udiff.html
      - There is no need to change the copyright, right?

  - http://cr.openjdk.java.net/~phh/8196989/webrev.02/test/hotspot/jtreg/gc/TestMemoryMXBeansAndPoolsPresence.java.udiff.html
     - the break seems to be on the wrong line, no?

+                }                break;


    - http://cr.openjdk.java.net/~phh/8196989/webrev.02/test/jdk/java/lang/management/MemoryMXBean/LowMemoryTest.java.udiff.html
    and
      http://cr.openjdk.java.net/~phh/8196989/webrev.02/test/jdk/java/lang/management/MemoryMXBean/MemoryManagement.java.udiff.html

+                        // In G1, humongous objects are tracked in the old space only in
+                        // legacy monitoring mode. In default mode, G1 tracks humongous
+                        // objects in the humongous space, which latter also supports a
+                        // usage threshold. Since we're allocating humongous objects in
+                        // this test, in default mode the old space doesn't change. For
+                        // this test, we use the old space in legacy mode (it's called
+                        // "G1 Old Gen" and the humongous space in default mode. If we
+                        // used "G1 Old Space" in default mode, notification would never
+                        // happen.

-> latter seems ot be the wrong word or something is missing in that sentence
-> the parenthesis is never closed (it's called.... is missing a ) somewhere

Thanks,
Jc

On Wed, Oct 17, 2018 at 1:18 PM Hohensee, Paul <hohensee at amazon.com<mailto:hohensee at amazon.com>> wrote:
Ping.

From: serviceability-dev <serviceability-dev-bounces at openjdk.java.net<mailto:serviceability-dev-bounces at openjdk.java.net>> on behalf of "Hohensee, Paul" <hohensee at amazon.com<mailto:hohensee at amazon.com>>
Date: Thursday, October 11, 2018 at 6:46 PM
To: "hotspot-gc-dev at openjdk.java.net<mailto:hotspot-gc-dev at openjdk.java.net>" <hotspot-gc-dev at openjdk.java.net<mailto:hotspot-gc-dev at openjdk.java.net>>, "serviceability-dev at openjdk.java.net<mailto:serviceability-dev at openjdk.java.net>" <serviceability-dev at openjdk.java.net<mailto:serviceability-dev at openjdk.java.net>>
Subject: Re: 8196989: Revamp G1 JMX MemoryPool and GarbageCollector MXBean definitions

Any takers? :)

From: serviceability-dev <serviceability-dev-bounces at openjdk.java.net<mailto:serviceability-dev-bounces at openjdk.java.net>> on behalf of "Hohensee, Paul" <hohensee at amazon.com<mailto:hohensee at amazon.com>>
Date: Monday, October 8, 2018 at 7:50 PM
To: "hotspot-gc-dev at openjdk.java.net<mailto:hotspot-gc-dev at openjdk.java.net>" <hotspot-gc-dev at openjdk.java.net<mailto:hotspot-gc-dev at openjdk.java.net>>, "serviceability-dev at openjdk.java.net<mailto:serviceability-dev at openjdk.java.net>" <serviceability-dev at openjdk.java.net<mailto:serviceability-dev at openjdk.java.net>>
Subject: RFR: 8196989: Revamp G1 JMX MemoryPool and GarbageCollector MXBean definitions

Bug: https://bugs.openjdk.java.net/browse/JDK-8196989
CSR: https://bugs.openjdk.java.net/browse/JDK-8196991
Webrev: http://cr.openjdk.java.net/~phh/8196989/webrev.02/

As requested, I split the jstat counter update off from the MXBean update. This is the MXBean update. The jstat counter RFE is https://bugs.openjdk.java.net/browse/JDK-8210965 and its CSR is https://bugs.openjdk.java.net/browse/JDK-8210966.

The MXBean CSR is in draft state, I’d greatly appreciate review and sign-off.

It’s been suggested that we add another pool to represent the free region set, but doing so would be incompatible with existing MXBean use invariants for all GCs. These are:


  1.  The sum of the pools’ MemoryUsage.max properties is the total reserved heap size.
  2.  The sum of the pools’ MemoryUsage.committed properties is the total committed size.
  3.  The sum of the pools’ MemoryUsage.used properties is the total size of the memory containing objects, live and dead-and-yet-to-be-collected, as the case might be, plus intentional gaps between them.
  4.  The total free space is (sum of the max properties – sum of the used properties).
  5.  The total uncommitted space is (sum of the max properties – sum of the committed properties).
  6.  The total committed free space is (2) – (3).

To keep invariants 1, 2 and 3, the free region pool’s “max” property should be “undefined” (i.e., -1). The intuitive, to me, “used” property value would be the total free space, but that would violate invariant 4 above. Defining the “committed” property as the total committed free space would violate invariants 2 and 6.

The patch passes the submit repo, hotspot tier1, and, separately, the serviceability, jfr, and gc jtreg tests. I’m uncertain how to construct a test that checks for valid MXBean content: the existing tests don’t. Any such test will be fragile due to possible future Hotspot changes that affect the values, and to run-to-run variability. I’ve done by-hand comparisons between the old and new MXBean content using the SwingSet2 demo, including using App CDS, and the numbers look reasonable.

The guts of the change are in G1MonitoringSupport::recalculate_sizes, initialize_serviceability, memory_managers, memory_pools, and G1MonitoringScope. I also defined TraceConcMemoryManagerStats to track the concurrent cycle in a way analogous to TraceCMSMemoryManagerStats. The changes to the includes in g1FullGCOopClosures.inline.hpp and g1HeapVerifier.cpp are to satisfy compiler complaints. I changed the 3rd argument to the G1MonitoringScope constructor to a mixed_gc flag, and use accessor methods instead of direct field accesses when accessor methods exist. I believe I’ve minimized the latter. I updated the copyright date to 2018 in memoryService.hpp because I neglected to do so in my previous G1 MXBean patch.

Thanks,

Paul




--

Thanks,
Jc
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