diff --git a/doc/contributing/documentation_guide.md b/doc/contributing/documentation_guide.md
index 8a73543e6c9076..29a1c72b02f0de 100644
--- a/doc/contributing/documentation_guide.md
+++ b/doc/contributing/documentation_guide.md
@@ -326,6 +326,16 @@ Alternatives:
     - Example {source}[https://github.com/ruby/ruby/blob/34d802f32f00df1ac0220b62f72605827c16bad8/doc/contributing/glossary.md?plain=1].
     - Corresponding {output}[https://docs.ruby-lang.org/en/master/contributing/glossary_md.html].
 
+### Languages in Examples
+
+For symbols and strings in documentation examples:
+
+- Prefer \English in \English documentation:  <tt>'Hello'</tt>.
+- Prefer Japanese in Japanese documentation:  <tt>'こんにちは'</tt>.
+- If a second language is needed (as, for example, characters with different byte-sizes),
+  prefer Japanese in \English documentation and \English in Japanese documentation.
+- Use other languages examples only as necessary:  see String#capitalize.
+
 ## Documenting Classes and Modules
 
 The general structure of the class or module documentation should be:
diff --git a/gc/mmtk/src/api.rs b/gc/mmtk/src/api.rs
index b99cbdc939f151..d735a81cac810d 100644
--- a/gc/mmtk/src/api.rs
+++ b/gc/mmtk/src/api.rs
@@ -4,6 +4,7 @@
 
 use mmtk::util::alloc::BumpPointer;
 use mmtk::util::alloc::ImmixAllocator;
+use mmtk::util::conversions;
 use mmtk::util::options::PlanSelector;
 use std::str::FromStr;
 use std::sync::atomic::Ordering;
@@ -13,6 +14,8 @@ use crate::abi::RubyBindingOptions;
 use crate::abi::RubyUpcalls;
 use crate::binding;
 use crate::binding::RubyBinding;
+use crate::heap::RubyHeapTriggerConfig;
+use crate::heap::RUBY_HEAP_TRIGGER_CONFIG;
 use crate::mmtk;
 use crate::utils::default_heap_max;
 use crate::utils::parse_capacity;
@@ -79,6 +82,29 @@ fn mmtk_builder_default_parse_heap_max() -> usize {
     parse_env_var_with("MMTK_HEAP_MAX", parse_capacity).unwrap_or_else(default_heap_max)
 }
 
+fn parse_float_env_var(key: &str, default: f64, min: f64, max: f64) -> f64 {
+    parse_env_var_with(key, |s| {
+        let mut float = f64::from_str(s).unwrap_or(default);
+
+        if float <= min {
+            eprintln!(
+                "{key} has value {float} which must be greater than {min}, using default instead"
+            );
+            float = default;
+        }
+
+        if float >= max {
+            eprintln!(
+                "{key} has value {float} which must be less than {max}, using default instead"
+            );
+            float = default;
+        }
+
+        Some(float)
+    })
+    .unwrap_or(default)
+}
+
 fn mmtk_builder_default_parse_heap_mode(heap_min: usize, heap_max: usize) -> GCTriggerSelector {
     let make_fixed = || GCTriggerSelector::FixedHeapSize(heap_max);
     let make_dynamic = || GCTriggerSelector::DynamicHeapSize(heap_min, heap_max);
@@ -86,6 +112,25 @@ fn mmtk_builder_default_parse_heap_mode(heap_min: usize, heap_max: usize) -> GCT
     parse_env_var_with("MMTK_HEAP_MODE", |s| match s {
         "fixed" => Some(make_fixed()),
         "dynamic" => Some(make_dynamic()),
+        "ruby" => {
+            let min_ratio = parse_float_env_var("RUBY_GC_HEAP_FREE_SLOTS_MIN_RATIO", 0.2, 0.0, 1.0);
+            let goal_ratio =
+                parse_float_env_var("RUBY_GC_HEAP_FREE_SLOTS_GOAL_RATIO", 0.4, min_ratio, 1.0);
+            let max_ratio =
+                parse_float_env_var("RUBY_GC_HEAP_FREE_SLOTS_MAX_RATIO", 0.65, goal_ratio, 1.0);
+
+            crate::heap::RUBY_HEAP_TRIGGER_CONFIG
+                .set(RubyHeapTriggerConfig {
+                    min_heap_pages: conversions::bytes_to_pages_up(heap_min),
+                    max_heap_pages: conversions::bytes_to_pages_up(heap_max),
+                    heap_pages_min_ratio: min_ratio,
+                    heap_pages_goal_ratio: goal_ratio,
+                    heap_pages_max_ratio: max_ratio,
+                })
+                .unwrap_or_else(|_| panic!("RUBY_HEAP_TRIGGER_CONFIG is already set"));
+
+            Some(GCTriggerSelector::Delegated)
+        }
         _ => None,
     })
     .unwrap_or_else(make_dynamic)
@@ -146,7 +191,7 @@ pub unsafe extern "C" fn mmtk_init_binding(
 
     crate::set_panic_hook();
 
-    let builder = unsafe { Box::from_raw(builder) };
+    let builder: Box<MMTKBuilder> = unsafe { Box::from_raw(builder) };
     let binding_options = RubyBindingOptions {
         ractor_check_mode: false,
         suffix_size: 0,
@@ -388,11 +433,12 @@ pub extern "C" fn mmtk_plan() -> *const u8 {
 pub extern "C" fn mmtk_heap_mode() -> *const u8 {
     static FIXED_HEAP: &[u8] = b"fixed\0";
     static DYNAMIC_HEAP: &[u8] = b"dynamic\0";
+    static RUBY_HEAP: &[u8] = b"ruby\0";
 
     match *crate::BINDING.get().unwrap().mmtk.get_options().gc_trigger {
         GCTriggerSelector::FixedHeapSize(_) => FIXED_HEAP.as_ptr(),
         GCTriggerSelector::DynamicHeapSize(_, _) => DYNAMIC_HEAP.as_ptr(),
-        _ => panic!("Unknown heap mode"),
+        GCTriggerSelector::Delegated => RUBY_HEAP.as_ptr(),
     }
 }
 
@@ -401,7 +447,12 @@ pub extern "C" fn mmtk_heap_min() -> usize {
     match *crate::BINDING.get().unwrap().mmtk.get_options().gc_trigger {
         GCTriggerSelector::FixedHeapSize(_) => 0,
         GCTriggerSelector::DynamicHeapSize(min_size, _) => min_size,
-        _ => panic!("Unknown heap mode"),
+        GCTriggerSelector::Delegated => conversions::pages_to_bytes(
+            RUBY_HEAP_TRIGGER_CONFIG
+                .get()
+                .expect("RUBY_HEAP_TRIGGER_CONFIG not set")
+                .min_heap_pages,
+        ),
     }
 }
 
@@ -410,7 +461,12 @@ 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"),
+        GCTriggerSelector::Delegated => conversions::pages_to_bytes(
+            RUBY_HEAP_TRIGGER_CONFIG
+                .get()
+                .expect("RUBY_HEAP_TRIGGER_CONFIG not set")
+                .max_heap_pages,
+        ),
     }
 }
 
diff --git a/gc/mmtk/src/collection.rs b/gc/mmtk/src/collection.rs
index 41c508afd9115d..824747b04c4051 100644
--- a/gc/mmtk/src/collection.rs
+++ b/gc/mmtk/src/collection.rs
@@ -1,9 +1,11 @@
 use crate::abi::GCThreadTLS;
 
 use crate::api::RubyMutator;
+use crate::heap::RubyHeapTrigger;
 use crate::{mmtk, upcalls, Ruby};
 use mmtk::memory_manager;
 use mmtk::scheduler::*;
+use mmtk::util::heap::GCTriggerPolicy;
 use mmtk::util::{VMMutatorThread, VMThread, VMWorkerThread};
 use mmtk::vm::{Collection, GCThreadContext};
 use std::sync::atomic::Ordering;
@@ -67,6 +69,10 @@ impl Collection<Ruby> for VMCollection {
     fn vm_live_bytes() -> usize {
         (upcalls().vm_live_bytes)()
     }
+
+    fn create_gc_trigger() -> Box<dyn GCTriggerPolicy<Ruby>> {
+        Box::new(RubyHeapTrigger::default())
+    }
 }
 
 impl VMCollection {
diff --git a/gc/mmtk/src/heap/mod.rs b/gc/mmtk/src/heap/mod.rs
new file mode 100644
index 00000000000000..6af7c1b2e50682
--- /dev/null
+++ b/gc/mmtk/src/heap/mod.rs
@@ -0,0 +1,4 @@
+mod ruby_heap_trigger;
+pub use ruby_heap_trigger::RubyHeapTrigger;
+pub use ruby_heap_trigger::RubyHeapTriggerConfig;
+pub use ruby_heap_trigger::RUBY_HEAP_TRIGGER_CONFIG;
diff --git a/gc/mmtk/src/heap/ruby_heap_trigger.rs b/gc/mmtk/src/heap/ruby_heap_trigger.rs
new file mode 100644
index 00000000000000..9215e2ebb0ec04
--- /dev/null
+++ b/gc/mmtk/src/heap/ruby_heap_trigger.rs
@@ -0,0 +1,104 @@
+use std::sync::atomic::{AtomicUsize, Ordering};
+
+use mmtk::util::heap::GCTriggerPolicy;
+use mmtk::util::heap::SpaceStats;
+use mmtk::Plan;
+use mmtk::MMTK;
+use once_cell::sync::OnceCell;
+
+use crate::Ruby;
+
+pub static RUBY_HEAP_TRIGGER_CONFIG: OnceCell<RubyHeapTriggerConfig> = OnceCell::new();
+
+pub struct RubyHeapTriggerConfig {
+    /// Min heap size
+    pub min_heap_pages: usize,
+    /// Max heap size
+    pub max_heap_pages: usize,
+    /// Minimum ratio of empty space after a GC before the heap will grow
+    pub heap_pages_min_ratio: f64,
+    /// Ratio the heap will grow by
+    pub heap_pages_goal_ratio: f64,
+    /// Maximum ratio of empty space after a GC before the heap will shrink
+    pub heap_pages_max_ratio: f64,
+}
+
+pub struct RubyHeapTrigger {
+    /// Target number of heap pages
+    target_heap_pages: AtomicUsize,
+}
+
+impl GCTriggerPolicy<Ruby> for RubyHeapTrigger {
+    fn is_gc_required(
+        &self,
+        space_full: bool,
+        space: Option<SpaceStats<Ruby>>,
+        plan: &dyn Plan<VM = Ruby>,
+    ) -> bool {
+        // Let the plan decide
+        plan.collection_required(space_full, space)
+    }
+
+    fn on_gc_end(&self, mmtk: &'static MMTK<Ruby>) {
+        if let Some(plan) = mmtk.get_plan().generational() {
+            if plan.is_current_gc_nursery() {
+                // Nursery GC
+            } else {
+                // Full GC
+            }
+
+            panic!("TODO: support for generational GC not implemented")
+        } else {
+            let used_pages = mmtk.get_plan().get_used_pages();
+
+            let target_min =
+                (used_pages as f64 * (1.0 + Self::get_config().heap_pages_min_ratio)) as usize;
+            let target_max =
+                (used_pages as f64 * (1.0 + Self::get_config().heap_pages_max_ratio)) as usize;
+            let new_target =
+                (((used_pages as f64) * (1.0 + Self::get_config().heap_pages_goal_ratio)) as usize)
+                    .clamp(
+                        Self::get_config().min_heap_pages,
+                        Self::get_config().max_heap_pages,
+                    );
+
+            if used_pages < target_min || used_pages > target_max {
+                self.target_heap_pages.store(new_target, Ordering::Relaxed);
+            }
+        }
+    }
+
+    fn is_heap_full(&self, plan: &dyn Plan<VM = Ruby>) -> bool {
+        plan.get_reserved_pages() > self.target_heap_pages.load(Ordering::Relaxed)
+    }
+
+    fn get_current_heap_size_in_pages(&self) -> usize {
+        self.target_heap_pages.load(Ordering::Relaxed)
+    }
+
+    fn get_max_heap_size_in_pages(&self) -> usize {
+        Self::get_config().max_heap_pages
+    }
+
+    fn can_heap_size_grow(&self) -> bool {
+        self.target_heap_pages.load(Ordering::Relaxed) < Self::get_config().max_heap_pages
+    }
+}
+
+impl Default for RubyHeapTrigger {
+    fn default() -> Self {
+        let min_heap_pages = Self::get_config().min_heap_pages;
+
+        Self {
+            target_heap_pages: AtomicUsize::new(min_heap_pages),
+        }
+    }
+}
+
+impl RubyHeapTrigger {
+    fn get_config<'b>() -> &'b RubyHeapTriggerConfig {
+        RUBY_HEAP_TRIGGER_CONFIG
+            .get()
+            .expect("Attempt to use RUBY_HEAP_TRIGGER_CONFIG before it is initialized")
+    }
+}
diff --git a/gc/mmtk/src/lib.rs b/gc/mmtk/src/lib.rs
index 4bcafb597a2bb6..8647793522ed82 100644
--- a/gc/mmtk/src/lib.rs
+++ b/gc/mmtk/src/lib.rs
@@ -25,6 +25,7 @@ pub mod active_plan;
 pub mod api;
 pub mod binding;
 pub mod collection;
+pub mod heap;
 pub mod object_model;
 pub mod reference_glue;
 pub mod scanning;
diff --git a/set.c b/set.c
index 734a6ecaea2107..469078ee9968af 100644
--- a/set.c
+++ b/set.c
@@ -697,7 +697,7 @@ set_i_join(int argc, VALUE *argv, VALUE set)
  *  call-seq:
  *    add(obj) -> self
  *
- *  Adds the given object to the set and returns self.  Use `merge` to
+ *  Adds the given object to the set and returns self. Use Set#merge to
  *  add many elements at once.
  *
  *    Set[1, 2].add(3)                    #=> Set[1, 2, 3]