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Always use fixed heap for NoGC #113

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Merged
peterzhu2118 merged 1 commit into from
Sep 18, 2026
Merged

Always use fixed heap for NoGC #113

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30 changes: 26 additions & 4 deletions gc/mmtk/src/api.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -106,14 +106,25 @@ fn parse_float_env_var(key: &str, default: f64, min: f64, max: f64) -> f64 {
.unwrap_or(default)
}

fn mmtk_builder_default_parse_heap_mode(heap_min: usize, heap_max: usize) -> GCTriggerSelector {
fn mmtk_builder_default_parse_heap_mode(
heap_min: usize,
heap_max: usize,
plan: PlanSelector,
) -> GCTriggerSelector {
let make_fixed = || GCTriggerSelector::FixedHeapSize(heap_max);
let make_dynamic = || GCTriggerSelector::DynamicHeapSize(heap_min, heap_max);

parse_env_var_with("MMTK_HEAP_MODE", |s| match s {
"fixed" => Some(make_fixed()),
"dynamic" => Some(make_dynamic()),
"ruby" => {
if plan == PlanSelector::NoGC {
eprintln!(
"[WARN] Cannot use ruby heap mode with NoGC. Using fixed heap mode instead."
);
return Some(make_fixed());
}

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);
Expand All @@ -133,6 +144,13 @@ fn mmtk_builder_default_parse_heap_mode(heap_min: usize, heap_max: usize) -> GCT
Some(GCTriggerSelector::Delegated)
}
"cpu" => {
if plan == PlanSelector::NoGC {
eprintln!(
"[WARN] Cannot use cpu heap mode with NoGC. Using fixed heap mode instead."
);
return Some(make_fixed());
}

// CPU-overhead-driven heap sizing based on Tavakolisomeh et al.,
// "Heap Size Adjustment with CPU Control", MPLR '23.
//
Expand Down Expand Up @@ -206,12 +224,16 @@ pub extern "C" fn mmtk_builder_default() -> *mut MMTKBuilder {
std::process::exit(1);
}

let plan = mmtk_builder_default_parse_plan();

builder.options.plan.set(plan);

builder
.options
.gc_trigger
.set(mmtk_builder_default_parse_heap_mode(heap_min, heap_max));

builder.options.plan.set(mmtk_builder_default_parse_plan());
.set(mmtk_builder_default_parse_heap_mode(
heap_min, heap_max, plan,
));

Box::into_raw(Box::new(builder))
}
Expand Down
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