From 6a78ffaf164d373b5ad022dc211e2ff34cf18a13 Mon Sep 17 00:00:00 2001
From: Peter Zhu <peter@peterzhu.ca>
Date: Fri, 17 Jan 2025 10:44:16 -0500
Subject: [PATCH] Add mmtk_heap_max to GC.config

---
 gc/mmtk/mmtk.c                  | 1 +
 gc/mmtk/mmtk.h                  | 2 ++
 gc/mmtk/src/api.rs              | 9 +++++++++
 test/mmtk/test_configuration.rb | 6 ++++++
 4 files changed, 18 insertions(+)

diff --git a/gc/mmtk/mmtk.c b/gc/mmtk/mmtk.c
index b5be2c2..75f0362 100644
--- a/gc/mmtk/mmtk.c
+++ b/gc/mmtk/mmtk.c
@@ -637,6 +637,7 @@ rb_gc_impl_config_get(void *objspace_ptr)
     rb_hash_aset(hash, ID2SYM(rb_intern_const("mmtk_heap_mode")), rb_str_new_cstr((const char *)mmtk_heap_mode()));
     size_t heap_min = mmtk_heap_min();
     if (heap_min > 0) rb_hash_aset(hash, ID2SYM(rb_intern_const("mmtk_heap_min")), RB_ULONG2NUM(heap_min));
+    rb_hash_aset(hash, ID2SYM(rb_intern_const("mmtk_heap_max")), RB_ULONG2NUM(mmtk_heap_max()));
 
     return hash;
 }
diff --git a/gc/mmtk/mmtk.h b/gc/mmtk/mmtk.h
index fdd6d0c..00004df 100644
--- a/gc/mmtk/mmtk.h
+++ b/gc/mmtk/mmtk.h
@@ -153,6 +153,8 @@ const uint8_t *mmtk_heap_mode(void);
 
 size_t mmtk_heap_min(void);
 
+size_t mmtk_heap_max(void);
+
 bool mmtk_is_mmtk_object(MMTk_Address addr);
 
 #endif  /* MMTK_H */
diff --git a/gc/mmtk/src/api.rs b/gc/mmtk/src/api.rs
index 00a7846..91718ce 100644
--- a/gc/mmtk/src/api.rs
+++ b/gc/mmtk/src/api.rs
@@ -368,6 +368,15 @@ pub extern "C" fn mmtk_heap_min() -> usize {
     }
 }
 
+#[no_mangle]
+pub extern "C" fn mmtk_heap_max() -> usize {
+    match *crate::BINDING.get().unwrap().mmtk.get_options().gc_trigger {
+        GCTriggerSelector::FixedHeapSize(max_size) => max_size,
+        GCTriggerSelector::DynamicHeapSize(_, max_size) => max_size,
+        _ => panic!("Unknown heap mode")
+    }
+}
+
 // =============== Miscellaneous ===============
 
 #[no_mangle]
diff --git a/test/mmtk/test_configuration.rb b/test/mmtk/test_configuration.rb
index 56f87af..0f60eb6 100644
--- a/test/mmtk/test_configuration.rb
+++ b/test/mmtk/test_configuration.rb
@@ -39,6 +39,12 @@ def test_MMTK_HEAP_MIN
       RUBY
     end
 
+    def test_MMTK_HEAP_MAX
+      assert_separately([{ "MMTK_HEAP_MODE" => "fixed", "MMTK_HEAP_MAX" => "100MiB" }], <<~RUBY)
+        assert_equal(100 * 1024 * 1024, GC.config[:mmtk_heap_max])
+      RUBY
+    end
+
     %w(MMTK_THREADS MMTK_HEAP_MIN MMTK_HEAP_MAX MMTK_HEAP_MODE MMTK_PLAN).each do |var|
       define_method(:"test_invalid_#{var}") do
         exit_code = assert_in_out_err(