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<p class="MsoNormal"><span style="font-size:11.0pt">Bug: https://bugs.openjdk.java.net/browse/JDK-8196989<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">CSR: https://bugs.openjdk.java.net/browse/JDK-8196991<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Webrev: http://cr.openjdk.java.net/~phh/8196989/webrev.02/<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">As requested, I split the jstat counter update off from the MXBean update. This is the MXBean update. The jstat counter RFE is
<a href="https://bugs.openjdk.java.net/browse/JDK-8210965">https://bugs.openjdk.java.net/browse/JDK-8210965</a> and its CSR is
<a href="https://bugs.openjdk.java.net/browse/JDK-8210966">https://bugs.openjdk.java.net/browse/JDK-8210966</a>.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">The MXBean CSR is in draft state, I’d greatly appreciate review and sign-off.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">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:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<ol style="margin-top:0in" start="1" type="1">
<li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1"><span style="font-size:11.0pt">The sum of the pools’ MemoryUsage.max properties is the total reserved heap size.<o:p></o:p></span></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1"><span style="font-size:11.0pt">The sum of the pools’ MemoryUsage.committed properties is the total committed size.<o:p></o:p></span></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1"><span style="font-size:11.0pt">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.<o:p></o:p></span></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1"><span style="font-size:11.0pt">The total free space is (sum of the max properties – sum of the used properties).<o:p></o:p></span></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1"><span style="font-size:11.0pt">The total uncommitted space is (sum of the max properties – sum of the committed properties).<o:p></o:p></span></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1"><span style="font-size:11.0pt">The total committed free space is (2) – (3).<o:p></o:p></span></li></ol>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">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.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">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.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">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 3<sup>rd</sup> 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.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Thanks,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Paul<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
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