Adding stock gc trigger and set it as default (#222)

This PR implements Julia's Stock GC heuristics for triggering GC and
resizing the heap. It also updates `mmtk-core` to the latest version.

Author: udesou

mmtk/Cargo.lock

@@ -27,7 +27,7 @@ lazy_static = "1.1"
 # - change branch
 # - change repo name
 # But other changes including adding/removing whitespaces in commented lines may break the CI
-mmtk = { git = "https://github.com/mmtk/mmtk-core.git", rev = "ec745353a8de72b645613e0fef3ab7f5f1ad9bd1" }
+mmtk = { git = "https://github.com/mmtk/mmtk-core.git", rev = "051bc7470feef915c445305301e6113f86d3957b" }
 # Uncomment the following to build locally
 # mmtk = { path = "../repos/mmtk-core" }
 log = {version = "0.4", features = ["max_level_trace", "release_max_level_off"] }

mmtk/Cargo.toml

@@ -53,7 +53,16 @@ pub extern "C" fn mmtk_gc_init(
 
         // Set heap size
         let success =
-            if min_heap_size != 0 {
+            // By default min and max heap size are 0, and we use the Stock GC heuristics
+            if min_heap_size == 0 && max_heap_size == 0 {
+                info!(
+                    "Setting mmtk heap size to use Stock GC heuristics as defined in gc_trigger.rs",
+                );
+                builder
+                    .options
+                    .gc_trigger
+                    .set(mmtk::util::options::GCTriggerSelector::Delegated)
+            } else if min_heap_size != 0 {
                 info!(
                     "Setting mmtk heap size to a variable size with min-max of {}-{} (in bytes)",
                     min_heap_size, max_heap_size

mmtk/src/api.rs

@@ -1,19 +1,20 @@
 use crate::SINGLETON;
 use crate::{
-    jl_gc_prepare_to_collect, jl_gc_update_stats, jl_get_gc_disable_counter, jl_hrtime,
-    jl_throw_out_of_memory_error,
+    jl_gc_get_max_memory, jl_gc_prepare_to_collect, jl_gc_update_stats, jl_get_gc_disable_counter,
+    jl_hrtime, jl_throw_out_of_memory_error,
 };
 use crate::{JuliaVM, USER_TRIGGERED_GC};
 use log::{info, trace};
 use mmtk::util::alloc::AllocationError;
+use mmtk::util::heap::GCTriggerPolicy;
 use mmtk::util::opaque_pointer::*;
 use mmtk::vm::{Collection, GCThreadContext};
 use mmtk::Mutator;
 use std::sync::atomic::{AtomicBool, AtomicIsize, AtomicU64, Ordering};
 
 use crate::{BLOCK_FOR_GC, STW_COND, WORLD_HAS_STOPPED};
 
-static GC_START: AtomicU64 = AtomicU64::new(0);
+pub static GC_START: AtomicU64 = AtomicU64::new(0);
 
 pub struct VMCollection {}
 
@@ -111,6 +112,12 @@ impl Collection<JuliaVM> for VMCollection {
     fn is_collection_enabled() -> bool {
         unsafe { jl_get_gc_disable_counter() == 0 }
     }
+
+    fn create_gc_trigger() -> Box<dyn GCTriggerPolicy<JuliaVM>> {
+        use crate::gc_trigger::*;
+        let max_memory = unsafe { jl_gc_get_max_memory() };
+        Box::new(JuliaGCTrigger::new(max_memory))
+    }
 }
 
 pub fn is_current_gc_nursery() -> bool {