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Hi all,</div>
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Following up on the previous discussions around Automatic Heap Sizing (AHS) for G1, I wanted to summarize the key takeaways and outline the next steps.</div>
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In my November message [1], I described how AHS could dynamically manage heap sizing based on multiple inputs, including global memory pressure,
<code>GCTimeRatio</code> policy, and user-defined heap tunables. This aligns with Thomas’s summary [2], which outlines how AHS integrates with G1’s existing mechanisms, including CPU-based heap resizing (JDK-8238687) [3], external constraints like
<code>CurrentMaxHeapSize</code> (JDK-8204088) [4], and SoftMaxHeapSize (JDK-8236073) [5] as a key influence on heap adjustments.</div>
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AHS will operate as a broader mechanism, where <code>SoftMaxHeapSize</code> serves as a heuristic to guide memory management but does not impose strict limits. It will work in conjunction with CPU-based heuristics to manage heap growth and contraction efficiently.</div>
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Google’s previous work on <code>ProposedHeapSize</code> for G1 contributed valuable insights into adaptive heap management, but as discussions evolved, the consensus has shifted toward a model centered on
<code>SoftMaxHeapSize</code> as a guiding input within AHS.</div>
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Given this consensus, I will proceed with the implementation of JDK-8236073 [5] to ensure that AHS integrates effectively with G1’s dynamic heap sizing policies.</div>
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I will share updates as the work progresses. If there are any additional concerns or areas where further clarification is needed, please let me know.</div>
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Thanks again for the valuable discussions.</div>
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Best,<br>
Monica</div>
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<b>References</b></div>
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[1] Monica Beckwith, "Clarifications on AHS behavior and its role in G1," OpenJDK hotspot-gc-dev mailing list, November 2024.
<a href="https://mail.openjdk.org/pipermail/hotspot-gc-dev/2024-November/050191.html" target="_blank" id="OWAd8a90e5a-7cda-1542-2f52-e1e8f0f60faf" class="fui-Link ___1q1shib f2hkw1w f3rmtva f1ewtqcl fyind8e f1k6fduh f1w7gpdv fk6fouc fjoy568 figsok6 f1s184ao f1mk8lai fnbmjn9 f1o700av f13mvf36 f1cmlufx f9n3di6 f1ids18y f1tx3yz7 f1deo86v f1eh06m1 f1iescvh fhgqx19 f1olyrje f1p93eir f1nev41a f1h8hb77 f1lqvz6u f10aw75t fsle3fq f17ae5zn OWAAutoLink" title="https://mail.openjdk.org/pipermail/hotspot-gc-dev/2024-november/050191.html" rel="noreferrer noopener">
[</a><a href="https://mail.openjdk.org/pipermail/hotspot-gc-dev/2024-November/050191.html" target="_blank" id="OWAc4063047-6eaa-1454-d86e-f9ddcdfbc8ba" class="fui-Link ___1q1shib f2hkw1w f3rmtva f1ewtqcl fyind8e f1k6fduh f1w7gpdv fk6fouc fjoy568 figsok6 f1s184ao f1mk8lai fnbmjn9 f1o700av f13mvf36 f1cmlufx f9n3di6 f1ids18y f1tx3yz7 f1deo86v f1eh06m1 f1iescvh fhgqx19 f1olyrje f1p93eir f1nev41a f1h8hb77 f1lqvz6u f10aw75t fsle3fq f17ae5zn OWAAutoLink" title="https://mail.openjdk.org/pipermail/hotspot-gc-dev/2024-november/050191.html" rel="noreferrer noopener">https://mail.openjdk.org/pipermail/hotspot-gc-dev/2024-November/050191.html</a><a href="https://mail.openjdk.org/pipermail/hotspot-gc-dev/2024-November/XXXXXX.html]" target="_blank" id="OWAb1401868-fea1-f142-7cc9-052b37073837" class="fui-Link ___1q1shib f2hkw1w f3rmtva f1ewtqcl fyind8e f1k6fduh f1w7gpdv fk6fouc fjoy568 figsok6 f1s184ao f1mk8lai fnbmjn9 f1o700av f13mvf36 f1cmlufx f9n3di6 f1ids18y f1tx3yz7 f1deo86v f1eh06m1 f1iescvh fhgqx19 f1olyrje f1p93eir f1nev41a f1h8hb77 f1lqvz6u f10aw75t fsle3fq f17ae5zn OWAAutoLink" title="https://mail.openjdk.org/pipermail/hotspot-gc-dev/2024-november/xxxxxx.html]" rel="noreferrer noopener">]</a></div>
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[2] Thomas Schatzl, "Giving a rough summary about the system envisioned for G1," OpenJDK hotspot-gc-dev mailing list, February 2025. [<a href="https://mail.openjdk.org/pipermail/hotspot-gc-dev/2025-February/051069.html" target="_blank" id="OWA371203d6-7716-29bb-1c38-740286061b30" class="fui-Link ___1q1shib f2hkw1w f3rmtva f1ewtqcl fyind8e f1k6fduh f1w7gpdv fk6fouc fjoy568 figsok6 f1s184ao f1mk8lai fnbmjn9 f1o700av f13mvf36 f1cmlufx f9n3di6 f1ids18y f1tx3yz7 f1deo86v f1eh06m1 f1iescvh fhgqx19 f1olyrje f1p93eir f1nev41a f1h8hb77 f1lqvz6u f10aw75t fsle3fq f17ae5zn OWAAutoLink" title="https://mail.openjdk.org/pipermail/hotspot-gc-dev/2025-february/051069.html" rel="noreferrer noopener">https://mail.openjdk.org/pipermail/hotspot-gc-dev/2025-February/051069.html</a>]</div>
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[3] OpenJDK Issue, "JDK-8238687: Improve CPU-based heap sizing in G1," OpenJDK Bug Database. [<a href="https://bugs.openjdk.org/browse/JDK-8238687]" target="_blank" id="OWAae43d6da-2de4-9380-08ea-36bb5be8ef82" class="fui-Link ___1q1shib f2hkw1w f3rmtva f1ewtqcl fyind8e f1k6fduh f1w7gpdv fk6fouc fjoy568 figsok6 f1s184ao f1mk8lai fnbmjn9 f1o700av f13mvf36 f1cmlufx f9n3di6 f1ids18y f1tx3yz7 f1deo86v f1eh06m1 f1iescvh fhgqx19 f1olyrje f1p93eir f1nev41a f1h8hb77 f1lqvz6u f10aw75t fsle3fq f17ae5zn OWAAutoLink" title="https://bugs.openjdk.org/browse/jdk-8238687]" rel="noreferrer noopener">https://bugs.openjdk.org/browse/JDK-8238687]</a></div>
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[4] OpenJDK Issue, "JDK-8204088: Introduce CurrentMaxHeapSize to allow external heap constraints," OpenJDK Bug Database. [<a href="https://bugs.openjdk.org/browse/JDK-8204088]" target="_blank" id="OWA14e381ff-5f53-f4a1-ed2c-b05af74e572e" class="fui-Link ___1q1shib f2hkw1w f3rmtva f1ewtqcl fyind8e f1k6fduh f1w7gpdv fk6fouc fjoy568 figsok6 f1s184ao f1mk8lai fnbmjn9 f1o700av f13mvf36 f1cmlufx f9n3di6 f1ids18y f1tx3yz7 f1deo86v f1eh06m1 f1iescvh fhgqx19 f1olyrje f1p93eir f1nev41a f1h8hb77 f1lqvz6u f10aw75t fsle3fq f17ae5zn OWAAutoLink" title="https://bugs.openjdk.org/browse/jdk-8204088]" rel="noreferrer noopener">https://bugs.openjdk.org/browse/JDK-8204088]</a></div>
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[5] OpenJDK Issue, "JDK-8236073: Introduce SoftMaxHeapSize as a guide for G1 AHS," OpenJDK Bug Database. [<a href="https://bugs.openjdk.org/browse/JDK-8236073" target="_blank" id="OWAb7d7d155-90db-6e5a-702f-1b5430ea422b" class="fui-Link ___1q1shib f2hkw1w f3rmtva f1ewtqcl fyind8e f1k6fduh f1w7gpdv fk6fouc fjoy568 figsok6 f1s184ao f1mk8lai fnbmjn9 f1o700av f13mvf36 f1cmlufx f9n3di6 f1ids18y f1tx3yz7 f1deo86v f1eh06m1 f1iescvh fhgqx19 f1olyrje f1p93eir f1nev41a f1h8hb77 f1lqvz6u f10aw75t fsle3fq f17ae5zn OWAAutoLink" title="https://bugs.openjdk.org/browse/jdk-8236073" rel="noreferrer noopener">https://bugs.openjdk.org/browse/JDK-8236073</a>]</div>
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