mmtk · wks · Dec 1, 2025 · Nov 26, 2025 · Nov 27, 2025 · Nov 27, 2025
diff --git a/.github/workflows/auto-merge.yml b/.github/workflows/auto-merge.yml
@@ -31,14 +31,26 @@ jobs:
     with:
       pull_request: ${{ needs.get-merged-pr.outputs.pr }}
 
-  check-merge-openjdk-pr:
+  check-merge-openjdk11-pr:
     uses: ./.github/workflows/auto-merge-inner.yml
     needs: [get-merged-pr, binding-refs]
     with:
-      repo: ${{ needs.binding-refs.outputs.openjdk_binding_repo }}
-      base_repo: ${{ needs.binding-refs.outputs.openjdk_binding_repo_default }}
-      ref: ${{ needs.binding-refs.outputs.openjdk_binding_ref }}
-      base_ref: ${{ needs.binding-refs.outputs.openjdk_binding_ref_default }}
+      repo: ${{ needs.binding-refs.outputs.openjdk11_binding_repo }}
+      base_repo: ${{ needs.binding-refs.outputs.openjdk11_binding_repo_default }}
+      ref: ${{ needs.binding-refs.outputs.openjdk11_binding_ref }}
+      base_ref: ${{ needs.binding-refs.outputs.openjdk11_binding_ref_default }}
+      core_commit: ${{ needs.get-merged-pr.outputs.commit }}
+      update_lockfile: cargo build
+    secrets: inherit
+
+  check-merge-openjdk21-pr:
+    uses: ./.github/workflows/auto-merge-inner.yml
+    needs: [get-merged-pr, binding-refs]
+    with:
+      repo: ${{ needs.binding-refs.outputs.openjdk21_binding_repo }}
+      base_repo: ${{ needs.binding-refs.outputs.openjdk21_binding_repo_default }}
+      ref: ${{ needs.binding-refs.outputs.openjdk21_binding_ref }}
+      base_ref: ${{ needs.binding-refs.outputs.openjdk21_binding_ref_default }}
       core_commit: ${{ needs.get-merged-pr.outputs.commit }}
       update_lockfile: cargo build
     secrets: inherit

diff --git a/.github/workflows/extended-tests-bindings.yml b/.github/workflows/extended-tests-bindings.yml
@@ -62,13 +62,22 @@ jobs:
   #         .github/scripts/ci-test.sh
   #         .github/scripts/ci-style.sh
 
-  extended-tests-openjdk:
+  extended-tests-openjdk11:
     needs: binding-refs
     if: contains(github.event.pull_request.labels.*.name, 'PR-extended-testing')
     uses: ./.github/workflows/binding-tests-openjdk.yml
     with:
-      repo: ${{ needs.binding-refs.outputs.openjdk_binding_repo }}
-      ref: ${{ needs.binding-refs.outputs.openjdk_binding_ref }}
+      repo: ${{ needs.binding-refs.outputs.openjdk11_binding_repo }}
+      ref: ${{ needs.binding-refs.outputs.openjdk11_binding_ref }}
+      test-script: ci-test-extended.sh
+
+  extended-tests-openjdk21:
+    needs: binding-refs
+    if: contains(github.event.pull_request.labels.*.name, 'PR-extended-testing')
+    uses: ./.github/workflows/binding-tests-openjdk.yml
+    with:
+      repo: ${{ needs.binding-refs.outputs.openjdk21_binding_repo }}
+      ref: ${{ needs.binding-refs.outputs.openjdk21_binding_ref }}
       test-script: ci-test-extended.sh
 
   extended-tests-jikesrvm:

diff --git a/.github/workflows/merge-check.yml b/.github/workflows/merge-check.yml
@@ -26,7 +26,8 @@ env:
       "style-check/x86_64-unknown-linux-gnu/stable",
       "style-check/i686-unknown-linux-gnu/stable",
       "style-check/x86_64-apple-darwin/stable",
-      "extended-tests-openjdk / test",
+      "extended-tests-openjdk11 / test",
+      "extended-tests-openjdk21 / test",
       "extended-tests-v8",
       "extended-tests-jikesrvm",
       "extended-tests-julia",

diff --git a/.github/workflows/micro-bm.yml b/.github/workflows/micro-bm.yml
@@ -27,6 +27,9 @@ jobs:
         uses: qinsoon/comment-env-vars@1.1.0
         with:
           token: ${{ secrets.GITHUB_TOKEN }}
+          # TODO: If we plan to resurrect micro-bm, we need to get the trunk name from a unique .yml
+          # file so that all GitHub Actions scripts agree upon which branch is the trunk (e.g.
+          # jdk-11, jdk-21, ...).
           default_env: 'OPENJDK_BINDING_TRUNK_REF=master,MMTK_CORE_TRUNK_REF=master,OPENJDK_BINDING_BRANCH_REF=master,MMTK_CORE_BRANCH_REF=${{ github.event.pull_request.head.sha }}'
       # Trunk
       # - binding

diff --git a/.github/workflows/minimal-tests-bindings.yml b/.github/workflows/minimal-tests-bindings.yml
@@ -39,10 +39,18 @@ jobs:
     with:
       pull_request: ${{ needs.grace-period.outputs.pr-number }}
 
-  minimal-tests-openjdk:
+  minimal-tests-openjdk11:
     needs: binding-refs
     uses: ./.github/workflows/binding-tests-openjdk.yml
     with:
-      repo: ${{ needs.binding-refs.outputs.openjdk_binding_repo }}
-      ref: ${{ needs.binding-refs.outputs.openjdk_binding_ref }}
+      repo: ${{ needs.binding-refs.outputs.openjdk11_binding_repo }}
+      ref: ${{ needs.binding-refs.outputs.openjdk11_binding_ref }}
+      test-script: ci-test-minimal.sh
+
+  minimal-tests-openjdk21:
+    needs: binding-refs
+    uses: ./.github/workflows/binding-tests-openjdk.yml
+    with:
+      repo: ${{ needs.binding-refs.outputs.openjdk21_binding_repo }}
+      ref: ${{ needs.binding-refs.outputs.openjdk21_binding_ref }}
       test-script: ci-test-minimal.sh
diff --git a/.github/workflows/perf-compare-ci.yml b/.github/workflows/perf-compare-ci.yml
@@ -177,13 +177,15 @@ jobs:
         needs: [binding-refs, mmtk-refs]
         timeout-minutes: 1440
         steps:
-            # Trunk - we always use master from the mmtk org
+            # Trunk - we use the default repo and branch as specified in pr-binding-refs.
+            # TODO: We currently use OpenJDK 11 for performance comparison.
+            # We should switch to OpenJDK 21 when we are ready, and start a new epoch.
             # - binding
             - name: Checkout OpenJDK Binding Trunk
               uses: actions/checkout@v4
               with:
-                repository: mmtk/mmtk-openjdk
-                ref: master
+                repository: ${{ needs.binding-refs.outputs.openjdk11_binding_repo_default }}
+                ref: ${{ needs.binding-refs.outputs.openjdk11_binding_ref_default }}
                 path: mmtk-openjdk-trunk
             - name: Checkout OpenJDK for Trunk
               working-directory: mmtk-openjdk-trunk
@@ -200,8 +202,10 @@ jobs:
             - name: Checkout OpenJDK Binding Branch
               uses: actions/checkout@v4
               with:
-                repository: ${{ needs.binding-refs.outputs.openjdk_binding_repo }}
-                ref: ${{ needs.binding-refs.outputs.openjdk_binding_ref }}
+                # TODO: We currently use OpenJDK 11 for performance comparison.
+                # We should switch to OpenJDK 21 when we are ready, and start a new epoch.
+                repository: ${{ needs.binding-refs.outputs.openjdk11_binding_repo }}
+                ref: ${{ needs.binding-refs.outputs.openjdk11_binding_ref }}
                 path: mmtk-openjdk-branch
             - name: Checkout OpenJDK for Branch
               working-directory: mmtk-openjdk-branch

diff --git a/.github/workflows/perf-regression-ci.yml b/.github/workflows/perf-regression-ci.yml
@@ -129,6 +129,9 @@ jobs:
         uses: actions/checkout@v4
         with:
           repository: mmtk/mmtk-openjdk
+          # TODO: We currently use OpenJDK 11 for performance comparison.
+          # We should switch to OpenJDK 21 when we are ready, and start a new epoch.
+          ref: jdk-11
           path: latest/mmtk-openjdk
       - name: Checkout OpenJDK (latest)
         working-directory: latest/mmtk-openjdk

diff --git a/.github/workflows/pr-binding-refs.yml b/.github/workflows/pr-binding-refs.yml
@@ -12,10 +12,16 @@
 # to specify the binding pull requests. Note if any of the following values are omitted, the default values
 # will be used (run with the master in mmtk's binding repos).
 # Repo is in the format of user/repo. Ref could be sha or branch name.
+#
+# Note that OpenJDK 11 and OpenJDK 21 are considered two bindings, and their repo and ref names are
+# specified separately.  It is allowed to specify one or both of OpenJDK 11 and 21.
+#
 # ```
 # binding-refs
-# OPENJDK_BINDING_REPO=xx/xx
-# OPENJDK_BINDING_REF=xxxxxx
+# OPENJDK11_BINDING_REPO=xx/xx
+# OPENJDK11_BINDING_REF=xxxxxx
+# OPENJDK21_BINDING_REPO=xx/xx
+# OPENJDK21_BINDING_REF=xxxxxx
 # JIKESRVM_BINDING_REPO=xx/xx
 # JIKESRVM_BINDING_REF=xxxxxx
 # V8_BINDING_REPO=xx/xx
@@ -37,18 +43,31 @@ on:
         type: string
         required: true
     outputs:
-      openjdk_binding_repo:
-        description: "The repository of OpenJDK binding, such as {user}/{repo}"
-        value: ${{ jobs.binding-refs.outputs.openjdk_binding_repo}}
-      openjdk_binding_repo_default:
-        description: "The default repository of OpenJDK binding, such as {user}/{repo}"
-        value: ${{ jobs.binding-refs.outputs.openjdk_binding_repo_default }}
-      openjdk_binding_ref:
-        description: "The git ref of OpenJDK binding, such as sha and branch name"
-        value: ${{ jobs.binding-refs.outputs.openjdk_binding_ref}}
-      openjdk_binding_ref_default:
-        description: "The default git ref of OpenJDK binding, such as sha and branch name"
-        value: ${{ jobs.binding-refs.outputs.openjdk_binding_ref_default }}
+      openjdk11_binding_repo:
+        description: "The repository of OpenJDK 11 binding, such as {user}/{repo}"
+        value: ${{ jobs.binding-refs.outputs.openjdk11_binding_repo}}
+      openjdk11_binding_repo_default:
+        description: "The default repository of OpenJDK 11 binding, such as {user}/{repo}"
+        value: ${{ jobs.binding-refs.outputs.openjdk11_binding_repo_default }}
+      openjdk11_binding_ref:
+        description: "The git ref of OpenJDK 11 binding, such as sha and branch name"
+        value: ${{ jobs.binding-refs.outputs.openjdk11_binding_ref}}
+      openjdk11_binding_ref_default:
+        description: "The default git ref of OpenJDK 11 binding, such as sha and branch name"
+        value: ${{ jobs.binding-refs.outputs.openjdk11_binding_ref_default }}
+
+      openjdk21_binding_repo:
+        description: "The repository of OpenJDK 21 binding, such as {user}/{repo}"
+        value: ${{ jobs.binding-refs.outputs.openjdk21_binding_repo}}
+      openjdk21_binding_repo_default:
+        description: "The default repository of OpenJDK 21 binding, such as {user}/{repo}"
+        value: ${{ jobs.binding-refs.outputs.openjdk21_binding_repo_default }}
+      openjdk21_binding_ref:
+        description: "The git ref of OpenJDK 21 binding, such as sha and branch name"
+        value: ${{ jobs.binding-refs.outputs.openjdk21_binding_ref}}
+      openjdk21_binding_ref_default:
+        description: "The default git ref of OpenJDK 21 binding, such as sha and branch name"
+        value: ${{ jobs.binding-refs.outputs.openjdk21_binding_ref_default }}
 
       jikesrvm_binding_repo:
         description: "The repository of JikesRVM binding, such as {user}/{repo}"
@@ -121,8 +140,10 @@ jobs:
   binding-refs:
     runs-on: ubuntu-latest
     env:
-      OPENJDK_BINDING_REPO_DEFAULT: mmtk/mmtk-openjdk
-      OPENJDK_BINDING_REF_DEFAULT: master
+      OPENJDK11_BINDING_REPO_DEFAULT: mmtk/mmtk-openjdk
+      OPENJDK11_BINDING_REF_DEFAULT: jdk-11
+      OPENJDK21_BINDING_REPO_DEFAULT: mmtk/mmtk-openjdk
+      OPENJDK21_BINDING_REF_DEFAULT: jdk-21
       JIKESRVM_BINDING_REPO_DEFAULT: mmtk/mmtk-jikesrvm
       JIKESRVM_BINDING_REF_DEFAULT: master
       V8_BINDING_REPO_DEFAULT: mmtk/mmtk-v8
@@ -134,10 +155,14 @@ jobs:
       RUBY_BINDING_REPO_DEFAULT: mmtk/mmtk-ruby
       RUBY_BINDING_REF_DEFAULT: master
     outputs:
-        openjdk_binding_repo: ${{ steps.print.outputs.openjdk_binding_repo }}
-        openjdk_binding_repo_default: ${{ env.OPENJDK_BINDING_REPO_DEFAULT }}
-        openjdk_binding_ref: ${{ steps.print.outputs.openjdk_binding_ref }}
-        openjdk_binding_ref_default: ${{ env.OPENJDK_BINDING_REF_DEFAULT }}
+        openjdk11_binding_repo: ${{ steps.print.outputs.openjdk11_binding_repo }}
+        openjdk11_binding_repo_default: ${{ env.OPENJDK11_BINDING_REPO_DEFAULT }}
+        openjdk11_binding_ref: ${{ steps.print.outputs.openjdk11_binding_ref }}
+        openjdk11_binding_ref_default: ${{ env.OPENJDK11_BINDING_REF_DEFAULT }}
+        openjdk21_binding_repo: ${{ steps.print.outputs.openjdk21_binding_repo }}
+        openjdk21_binding_repo_default: ${{ env.OPENJDK21_BINDING_REPO_DEFAULT }}
+        openjdk21_binding_ref: ${{ steps.print.outputs.openjdk21_binding_ref }}
+        openjdk21_binding_ref_default: ${{ env.OPENJDK21_BINDING_REF_DEFAULT }}
         jikesrvm_binding_repo: ${{ steps.print.outputs.jikesrvm_binding_repo }}
         jikesrvm_binding_repo_default: ${{ env.JIKESRVM_BINDING_REPO_DEFAULT }}
         jikesrvm_binding_ref: ${{ steps.print.outputs.jikesrvm_binding_ref }}
@@ -164,11 +189,33 @@ jobs:
           with:
             pull_request: ${{ inputs.pull_request }}
             token: ${{ secrets.GITHUB_TOKEN }}
-            default_env: 'OPENJDK_BINDING_REPO=${{ env.OPENJDK_BINDING_REPO_DEFAULT }},OPENJDK_BINDING_REF=${{ env.OPENJDK_BINDING_REF_DEFAULT }},JIKESRVM_BINDING_REPO=${{ env.JIKESRVM_BINDING_REPO_DEFAULT }},JIKESRVM_BINDING_REF=${{ env.JIKESRVM_BINDING_REF_DEFAULT }},V8_BINDING_REPO=${{ env.V8_BINDING_REPO_DEFAULT }},V8_BINDING_REF=${{ env.V8_BINDING_REF_DEFAULT }},JULIA_BINDING_REPO=${{ env.JULIA_BINDING_REPO_DEFAULT }},JULIA_BINDING_REF=${{ env.JULIA_BINDING_REF_DEFAULT }},JULIA_VM_REPO=${{ env.JULIA_VM_REPO_DEFAULT }},JULIA_VM_REF=${{ env.JULIA_VM_REF_DEFAULT }},RUBY_BINDING_REPO=${{ env.RUBY_BINDING_REPO_DEFAULT }},RUBY_BINDING_REF=${{ env.RUBY_BINDING_REF_DEFAULT }}'
+            # Note: In the following lines, YAML makes one multi-line string literal from the
+            # indented lines after the '|' character, and then GitHub Actions replaces '${{ ... }}'
+            # with the expression values, and finally comment-env-vars parses the value of
+            # `default_env` (a multi-line string). comment-env-vars splits the string by /[\n\r,]/,
+            # and keeps only elements that contain non-blank sub-strings separated by '='.  Both the
+            # LHS and RHS of '=' are trimmed.
+            default_env: |
+              OPENJDK11_BINDING_REPO=${{ env.OPENJDK11_BINDING_REPO_DEFAULT }}
+              OPENJDK11_BINDING_REF=${{ env.OPENJDK11_BINDING_REF_DEFAULT }}
+              OPENJDK21_BINDING_REPO=${{ env.OPENJDK21_BINDING_REPO_DEFAULT }}
+              OPENJDK21_BINDING_REF=${{ env.OPENJDK21_BINDING_REF_DEFAULT }}
+              JIKESRVM_BINDING_REPO=${{ env.JIKESRVM_BINDING_REPO_DEFAULT }}
+              JIKESRVM_BINDING_REF=${{ env.JIKESRVM_BINDING_REF_DEFAULT }}
+              V8_BINDING_REPO=${{ env.V8_BINDING_REPO_DEFAULT }}
+              V8_BINDING_REF=${{ env.V8_BINDING_REF_DEFAULT }}
+              JULIA_BINDING_REPO=${{ env.JULIA_BINDING_REPO_DEFAULT }}
+              JULIA_BINDING_REF=${{ env.JULIA_BINDING_REF_DEFAULT }}
+              JULIA_VM_REPO=${{ env.JULIA_VM_REPO_DEFAULT }}
+              JULIA_VM_REF=${{ env.JULIA_VM_REF_DEFAULT }}
+              RUBY_BINDING_REPO=${{ env.RUBY_BINDING_REPO_DEFAULT }}
+              RUBY_BINDING_REF=${{ env.RUBY_BINDING_REF_DEFAULT }}
         - id: print
           run: |
-            echo "openjdk_binding_repo=${{ env.OPENJDK_BINDING_REPO }}" >> $GITHUB_OUTPUT
-            echo "openjdk_binding_ref=${{ env.OPENJDK_BINDING_REF }}" >> $GITHUB_OUTPUT
+            echo "openjdk11_binding_repo=${{ env.OPENJDK11_BINDING_REPO }}" >> $GITHUB_OUTPUT
+            echo "openjdk11_binding_ref=${{ env.OPENJDK11_BINDING_REF }}" >> $GITHUB_OUTPUT
+            echo "openjdk21_binding_repo=${{ env.OPENJDK21_BINDING_REPO }}" >> $GITHUB_OUTPUT
+            echo "openjdk21_binding_ref=${{ env.OPENJDK21_BINDING_REF }}" >> $GITHUB_OUTPUT
             echo "jikesrvm_binding_repo=${{ env.JIKESRVM_BINDING_REPO }}" >> $GITHUB_OUTPUT
             echo "jikesrvm_binding_ref=${{ env.JIKESRVM_BINDING_REF }}" >> $GITHUB_OUTPUT
             echo "v8_binding_repo=${{ env.V8_BINDING_REPO }}" >> $GITHUB_OUTPUT

diff --git a/.github/workflows/stress-ci.yml b/.github/workflows/stress-ci.yml
@@ -110,6 +110,9 @@ jobs:
         uses: actions/checkout@v4
         with:
           repository: mmtk/mmtk-openjdk
+          # TODO: If we plan to resurrect stress-ci, we need to get the trunk name from a unique .yml
+          # file so that all GitHub Actions scripts agree upon which branch is the trunk (e.g.
+          # jdk-11, jdk-21, ...).
           token: ${{ secrets.CI_ACCESS_TOKEN }}
           path: mmtk-openjdk
           submodules: true

diff --git a/docs/team/pull_request.md b/docs/team/pull_request.md
@@ -14,11 +14,18 @@ can be merged.
 If an MMTk core PR should be tested with other bindings PRs, one can specify the binding branch that
 should be tested with by adding a comment like below (see https://github.com/mmtk/mmtk-core/blob/master/.github/workflows/pr-binding-refs.yml).
 If there are multiple comments that match, the first one is effective. If the info is missing for
-a binding, the default repo (`mmtk/mmtk-X`) and branch (`master`) will be used instead.
+a binding, the default repo (`mmtk/mmtk-X`) and branch (`master` for most bindings) will be used instead.
+
+Note that OpenJDK 11 and OpenJDK 21 are considered two bindings.  Their default repos are both
+`mmtk/mmtk-openjdk`, but their default branches are `jdk-11` and `jdk-21`, respectively.  We can
+speficy the repo and branch of one of OpenJDK 11 and OpenJDK 21, or both.
+
 ```
 binding-refs
-OPENJDK_BINDING_REPO=xx/xx
-OPENJDK_BINDING_REF=xxxxxx
+OPENJDK11_BINDING_REPO=xx/xx
+OPENJDK11_BINDING_REF=xxxxxx
+OPENJDK21_BINDING_REPO=xx/xx
+OPENJDK21_BINDING_REF=xxxxxx
 JIKESRVM_BINDING_REPO=xx/xx
 JIKESRVM_BINDING_REF=xxxxxx
 V8_BINDING_REPO=xx/xx