runtime: build tag to turn off the finalizer pressure GC

src/runtime/gc_finalizer.go

@@ -33,10 +33,6 @@ type finalizerEntry struct {
 	fn interface{}
 }
 
-// finalizerGCThreshold starts pressure GC when registrations indicate external memory pressure.
-// Larger tables use a proportional threshold. Zero disables this trigger.
-const finalizerGCThreshold = 32
-
 var (
 	finalizers        *finalizerEntry // registered finalizers; a GC root that keeps fn values alive
 	finalizerPending  *finalizerEntry // finalizers whose object died, waiting to run

src/runtime/gc_finalizer_nopressure.go

@@ -0,0 +1,10 @@
+//go:build (gc.conservative || gc.precise) && runtime_nofinalizerpressure
+
+package runtime
+
+// finalizerGCThreshold is zero with the build tag runtime_nofinalizerpressure:
+// finalizer registrations do not start a collection, and finalizers run after
+// the collections the heap itself needs. For programs that register many
+// finalizers and go idle often, such as syscall/js programs, where every
+// js.Value registers one and every await is an idle.
+const finalizerGCThreshold = 0

src/runtime/gc_finalizer_pressure.go

@@ -0,0 +1,7 @@
+//go:build (gc.conservative || gc.precise) && !runtime_nofinalizerpressure
+
+package runtime
+
+// finalizerGCThreshold starts pressure GC when registrations indicate external memory pressure.
+// Larger tables use a proportional threshold. Zero disables this trigger.
+const finalizerGCThreshold = 32