Julia's stock GC trigger heuristics (#154)

This PR fixes Julia's GC trigger option/heuristics and enables it as
default (by changing the initial values to in `mmtk-gc.c`:
mmtk/julia#54).

Author: udesou

mmtk/Cargo.toml

@@ -10,7 +10,7 @@ edition = "2018"
 [package.metadata.julia]
 # Our CI matches the following line and extract mmtk/julia. If this line is updated, please check ci yaml files and make sure it works.
 julia_repo = "https://github.com/mmtk/julia.git"
-julia_version = "0ac54e680f9a8b57bb1fd8ef04919ce9898ae77b"
+julia_version = "5bb4714e34084ae851d2b6ecb2c1da0242c912c0"
 
 [lib]
 crate-type = ["cdylib"]

mmtk/src/api.rs

@@ -68,7 +68,12 @@ pub extern "C" fn mmtk_gc_init(
             // If MMTK_GC_TRIGGER is not set, then use the min/max heap size from the arguments.
             Err(_) => {
                 let success;
-                if min_heap_size != 0 {
+                if min_heap_size == 0 && max_heap_size == 0 {
+                    success = 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
@@ -271,9 +276,9 @@ pub extern "C" fn mmtk_handle_user_collection_request(tls: VMMutatorThread, coll
         // auto
         0 => memory_manager::handle_user_collection_request::<JuliaVM>(&SINGLETON, tls),
         // full
-        1 => SINGLETON.handle_user_collection_request(tls, true, true),
+        1 => SINGLETON.handle_user_collection_request(tls, false, true),
         // incremental
-        2 => SINGLETON.handle_user_collection_request(tls, true, false),
+        2 => SINGLETON.handle_user_collection_request(tls, false, false),
         _ => unreachable!(),
     }
 }

mmtk/src/gc_trigger.rs

@@ -39,7 +39,9 @@ pub struct JuliaGCTrigger {
     interval_all_threads: AtomicUsize,
     actual_allocd: AtomicUsize,
     prev_sweep_full: AtomicBool,
-
+    /// The number of pending allocation pages. The allocation requests for them have failed, and a GC is triggered.
+    /// We will need to take them into consideration so that the new heap size can accomodate those allocations.
+    pending_pages: AtomicUsize,
     last_recorded_reserved_pages: AtomicUsize,
 }
 
@@ -79,14 +81,18 @@ impl JuliaGCTrigger {
             actual_allocd: AtomicUsize::new(0),
             prev_sweep_full: AtomicBool::new(true),
             last_recorded_reserved_pages: AtomicUsize::new(0),
+            pending_pages: AtomicUsize::new(0),
         }
     }
 }
 
 impl GCTriggerPolicy<JuliaVM> for JuliaGCTrigger {
     fn on_gc_start(&self, mmtk: &'static MMTK<JuliaVM>) {
         let reserved_pages_in_last_gc = self.last_recorded_reserved_pages.load(Ordering::Relaxed);
-        let reserved_pages_now = mmtk.get_plan().get_reserved_pages();
+        // reserved pages now should include pending allocations
+        let reserved_pages_now =
+            mmtk.get_plan().get_reserved_pages() + self.pending_pages.load(Ordering::SeqCst);
+
         self.last_recorded_reserved_pages
             .store(reserved_pages_now, Ordering::Relaxed);
         self.actual_allocd.store(
@@ -110,7 +116,8 @@ impl GCTriggerPolicy<JuliaVM> for JuliaGCTrigger {
         let n_mutators = crate::active_plan::VMActivePlan::number_of_mutators();
 
         let reserved_pages_before_gc = self.last_recorded_reserved_pages.load(Ordering::Relaxed);
-        let reserved_pages_now = mmtk.get_plan().get_reserved_pages();
+        let reserved_pages_now =
+            mmtk.get_plan().get_reserved_pages() + self.pending_pages.load(Ordering::SeqCst);
         let freed = conversions::pages_to_bytes(
             reserved_pages_before_gc.saturating_sub(reserved_pages_now),
         );
@@ -122,7 +129,7 @@ impl GCTriggerPolicy<JuliaVM> for JuliaGCTrigger {
         // ignore large frontier (large frontier means the bytes of pointers reachable from the remset is larger than the default collect interval)
         let gc_auto = !mmtk.is_user_triggered_collection();
         let not_freed_enough = gc_auto
-            && (freed as f64) < (self.actual_allocd.load(Ordering::Relaxed) as f64 * 0.7f64);
+            && ((freed as f64) < (self.actual_allocd.load(Ordering::Relaxed) as f64 * 0.7f64));
         let mut sweep_full = false;
         if gc_auto {
             if not_freed_enough {
@@ -240,6 +247,13 @@ impl GCTriggerPolicy<JuliaVM> for JuliaGCTrigger {
             self.interval.load(Ordering::Relaxed) * n_mutators / 2,
             Ordering::Relaxed,
         );
+
+        // Clear pending allocation pages at the end of GC, no matter we used it or not.
+        self.pending_pages.store(0, Ordering::SeqCst);
+    }
+
+    fn on_pending_allocation(&self, pages: usize) {
+        self.pending_pages.fetch_add(pages, Ordering::SeqCst);
     }
 
     /// Is a GC required now?
@@ -249,9 +263,19 @@ impl GCTriggerPolicy<JuliaVM> for JuliaGCTrigger {
         space: Option<SpaceStats<JuliaVM>>,
         plan: &dyn Plan<VM = JuliaVM>,
     ) -> bool {
+        let reserved_pages_now = plan.get_reserved_pages();
+        let reserved_pages_before_gc = self.last_recorded_reserved_pages.load(Ordering::Relaxed);
+
         let allocd_so_far = conversions::pages_to_bytes(
-            plan.get_reserved_pages() - self.last_recorded_reserved_pages.load(Ordering::Relaxed),
+            reserved_pages_now.saturating_sub(reserved_pages_before_gc),
         );
+
+        trace!(
+            "Reserved now = {}, last recorded reserved = {}, Allocd so far: {}. interval_all_threads = {}",
+            plan.get_reserved_pages(), self.last_recorded_reserved_pages.load(Ordering::Relaxed), allocd_so_far,
+            self.interval_all_threads.load(Ordering::Relaxed)
+        );
+
         // Check against interval_all_threads, as we count allocation from all threads.
         if allocd_so_far > self.interval_all_threads.load(Ordering::Relaxed) {
             return true;