STW

fix-vm/Cargo.toml

@@ -14,6 +14,7 @@ smallvec = { workspace = true }
 string-interner = { workspace = true }
 likely_stable = { workspace = true }
 sptr = "0.3"
+sysinfo = { version = "0.38", default-features = false, features = ["system"] }
 
 fix-builtins = { path = "../fix-builtins" }
 fix-codegen = { path = "../fix-codegen" }

fix-vm/src/lib.rs

@@ -11,7 +11,7 @@ use fix_builtins::{BUILTINS, BuiltinId};
 use fix_codegen::InstructionPtr;
 use fix_common::StringId;
 use fix_error::{Error, Result, Source};
-use gc_arena::arena::CollectionPhase;
+use gc_arena::metrics::Pacing;
 use gc_arena::{Arena, Collect, Gc, Mutation, RefLock, Rootable};
 use hashbrown::HashMap;
 use num_enum::TryFromPrimitive;
@@ -485,6 +485,20 @@ enum Action {
     LoadFile(PendingLoad),
 }
 
+/// Compute initial heap size mirroring CppNix's strategy: 25% of physical RAM,
+/// clamped to [32 MiB, 384 MiB]. Used as `Pacing::min_sleep` so the collector
+/// defers the first cycle until the heap reaches this size.
+fn initial_heap_size() -> usize {
+    const MIN_SIZE: usize = 32 * 1024 * 1024;
+    const MAX_SIZE: usize = 384 * 1024 * 1024;
+
+    let mut sys = sysinfo::System::new();
+    sys.refresh_memory();
+    let total = sys.total_memory() as usize;
+    let quarter = total / 4;
+    quarter.clamp(MIN_SIZE, MAX_SIZE)
+}
+
 impl Vm<'_> {
     pub fn run<C: VmContext>(
         ctx: &mut C,
@@ -493,8 +507,10 @@ impl Vm<'_> {
     ) -> Result<fix_common::Value> {
         let (code, runtime) = ctx.split();
         let mut arena: Arena<Rootable![Vm<'_>]> = Arena::new(|mc| Vm::new(force_mode, mc, runtime));
-
-        const COLLECTOR_GRANULARITY: f64 = 1024.0;
+        arena.metrics().set_pacing(Pacing {
+            min_sleep: initial_heap_size(),
+            ..Pacing::STOP_THE_WORLD
+        });
 
         let mut pc = ip.0;
         loop {
@@ -502,12 +518,8 @@ impl Vm<'_> {
             match arena.mutate_root(|mc, root| root.dispatch_batch(bytecode, runtime, pc, mc)) {
                 Action::Continue { pc: new_pc } => {
                     pc = new_pc;
-                    if arena.metrics().allocation_debt() > COLLECTOR_GRANULARITY {
-                        if arena.collection_phase() == CollectionPhase::Sweeping {
-                            arena.collect_debt();
-                        } else if let Some(marked) = arena.mark_debt() {
-                            marked.start_sweeping();
-                        }
+                    if arena.metrics().allocation_debt() > 0.0 {
+                        arena.finish_cycle();
                     }
                 }
                 Action::LoadFile(load) => {