Allow nursery size to be proportional to the heap size (#1087)

This PR introduces different kinds of nursery size options, and by
default, we use a proportion of the heap size as the min nursery. This
PR should generally improve the generational plans' performance by
triggering a full heap GC more promptly. This PR mitigates the issue
identified in #594, but does not
fully fix the problem.

src/plan/generational/global.rs

@@ -40,11 +40,7 @@ pub struct CommonGenPlan<VM: VMBinding> {
 impl<VM: VMBinding> CommonGenPlan<VM> {
     pub fn new(mut args: CreateSpecificPlanArgs<VM>) -> Self {
         let nursery = CopySpace::new(
-            args.get_space_args(
-                "nursery",
-                true,
-                VMRequest::fixed_extent(args.global_args.options.get_max_nursery_bytes(), false),
-            ),
+            args.get_space_args("nursery", true, VMRequest::discontiguous()),
             true,
         );
         let full_heap_gc_count = args
@@ -102,7 +98,7 @@ impl<VM: VMBinding> CommonGenPlan<VM> {
         space: Option<SpaceStats<VM>>,
     ) -> bool {
         let cur_nursery = self.nursery.reserved_pages();
-        let max_nursery = self.common.base.options.get_max_nursery_pages();
+        let max_nursery = self.common.base.gc_trigger.get_max_nursery_pages();
         let nursery_full = cur_nursery >= max_nursery;
         trace!(
             "nursery_full = {:?} (nursery = {}, max_nursery = {})",
@@ -261,7 +257,7 @@ impl<VM: VMBinding> CommonGenPlan<VM> {
     /// whose value depends on which spaces have been released.
     pub fn should_next_gc_be_full_heap(plan: &dyn Plan<VM = VM>) -> bool {
         let available = plan.get_available_pages();
-        let min_nursery = plan.base().options.get_min_nursery_pages();
+        let min_nursery = plan.base().gc_trigger.get_min_nursery_pages();
         let next_gc_full_heap = available < min_nursery;
         trace!(
             "next gc will be full heap? {}, available pages = {}, min nursery = {}",

src/plan/generational/mod.rs

@@ -48,10 +48,8 @@ pub const GEN_CONSTRAINTS: PlanConstraints = PlanConstraints {
     barrier: ACTIVE_BARRIER,
     // We may trace duplicate edges in sticky immix (or any plan that uses object remembering barrier). See https://github.com/mmtk/mmtk-core/issues/743.
     may_trace_duplicate_edges: ACTIVE_BARRIER.equals(BarrierSelector::ObjectBarrier),
-    max_non_los_default_alloc_bytes: crate::util::rust_util::min_of_usize(
+    max_non_los_default_alloc_bytes:
         crate::plan::plan_constraints::MAX_NON_LOS_ALLOC_BYTES_COPYING_PLAN,
-        crate::util::options::NURSERY_SIZE,
-    ),
     needs_prepare_mutator: false,
     ..PlanConstraints::default()
 };

src/plan/sticky/immix/global.rs

@@ -140,8 +140,8 @@ impl<VM: VMBinding> Plan for StickyImmix<VM> {
     }
 
     fn collection_required(&self, space_full: bool, space: Option<SpaceStats<Self::VM>>) -> bool {
-        let nursery_full =
-            self.immix.immix_space.get_pages_allocated() > self.options().get_max_nursery_pages();
+        let nursery_full = self.immix.immix_space.get_pages_allocated()
+            > self.base().gc_trigger.get_max_nursery_pages();
         if space_full
             && space.is_some()
             && space.as_ref().unwrap().0.name() != self.immix.immix_space.name()

src/util/heap/gc_trigger.rs

@@ -4,8 +4,9 @@ use crate::global_state::GlobalState;
 use crate::plan::gc_requester::GCRequester;
 use crate::plan::Plan;
 use crate::policy::space::Space;
+use crate::util::constants::BYTES_IN_PAGE;
 use crate::util::conversions;
-use crate::util::options::{GCTriggerSelector, Options};
+use crate::util::options::{GCTriggerSelector, Options, DEFAULT_MAX_NURSERY, DEFAULT_MIN_NURSERY};
 use crate::vm::VMBinding;
 use crate::MMTK;
 use std::mem::MaybeUninit;
@@ -58,6 +59,10 @@ impl<VM: VMBinding> GCTrigger<VM> {
         self.plan.write(plan);
     }
 
+    fn plan(&self) -> &dyn Plan<VM = VM> {
+        unsafe { self.plan.assume_init() }
+    }
+
     /// This method is called periodically by the allocation subsystem
     /// (by default, each time a page is consumed), and provides the
     /// collector with an opportunity to collect.
@@ -101,8 +106,62 @@ impl<VM: VMBinding> GCTrigger<VM> {
 
     /// Check if the heap is full
     pub fn is_heap_full(&self) -> bool {
-        let plan = unsafe { self.plan.assume_init() };
-        self.policy.is_heap_full(plan)
+        self.policy.is_heap_full(self.plan())
+    }
+
+    /// Return upper bound of the nursery size (in number of bytes)
+    pub fn get_max_nursery_bytes(&self) -> usize {
+        use crate::util::options::NurserySize;
+        debug_assert!(self.plan().generational().is_some());
+        match *self.options.nursery {
+            NurserySize::Bounded { min: _, max } => max,
+            NurserySize::ProportionalBounded { min: _, max } => {
+                let heap_size_bytes =
+                    conversions::pages_to_bytes(self.policy.get_current_heap_size_in_pages());
+                let max_bytes = heap_size_bytes as f64 * max;
+                let max_bytes = conversions::raw_align_up(max_bytes as usize, BYTES_IN_PAGE);
+                if max_bytes > DEFAULT_MAX_NURSERY {
+                    warn!("Proportional nursery with max size {} ({}) is larger than DEFAULT_MAX_NURSERY ({}). Use DEFAULT_MAX_NURSERY instead.", max, max_bytes, DEFAULT_MAX_NURSERY);
+                    DEFAULT_MAX_NURSERY
+                } else {
+                    max_bytes
+                }
+            }
+            NurserySize::Fixed(sz) => sz,
+        }
+    }
+
+    /// Return lower bound of the nursery size (in number of bytes)
+    pub fn get_min_nursery_bytes(&self) -> usize {
+        use crate::util::options::NurserySize;
+        debug_assert!(self.plan().generational().is_some());
+        match *self.options.nursery {
+            NurserySize::Bounded { min, max: _ } => min,
+            NurserySize::ProportionalBounded { min, max: _ } => {
+                let min_bytes =
+                    conversions::pages_to_bytes(self.policy.get_current_heap_size_in_pages())
+                        as f64
+                        * min;
+                let min_bytes = conversions::raw_align_up(min_bytes as usize, BYTES_IN_PAGE);
+                if min_bytes < DEFAULT_MIN_NURSERY {
+                    warn!("Proportional nursery with min size {} ({}) is smaller than DEFAULT_MIN_NURSERY ({}). Use DEFAULT_MIN_NURSERY instead.", min, min_bytes, DEFAULT_MIN_NURSERY);
+                    DEFAULT_MIN_NURSERY
+                } else {
+                    min_bytes
+                }
+            }
+            NurserySize::Fixed(sz) => sz,
+        }
+    }
+
+    /// Return upper bound of the nursery size (in number of pages)
+    pub fn get_max_nursery_pages(&self) -> usize {
+        crate::util::conversions::bytes_to_pages_up(self.get_max_nursery_bytes())
+    }
+
+    /// Return lower bound of the nursery size (in number of pages)
+    pub fn get_min_nursery_pages(&self) -> usize {
+        crate::util::conversions::bytes_to_pages_up(self.get_min_nursery_bytes())
     }
 }
 
@@ -433,7 +492,7 @@ impl<VM: VMBinding> GCTriggerPolicy<VM> for MemBalancerTrigger {
                         // We reserve an extra of min nursery. This ensures that we will not trigger
                         // a full heap GC in the next GC (if available pages is smaller than min nursery, we will force a full heap GC)
                         mmtk.get_plan().get_collection_reserved_pages()
-                            + mmtk.options.get_min_nursery_pages(),
+                            + mmtk.gc_trigger.get_min_nursery_pages(),
                         stats,
                     );
                 }