Implement mem balancer (#724)

This PR implements mem balancer (https://dl.acm.org/doi/pdf/10.1145/3563323).

Changes:
* Introduce a trait `GenerationalPlan: Plan`, and move methods that are specific to generational plans to the new trait from the old `trait Plan`.
* Change the return type of `Plan::generational()` to return an option of `&dyn GenerationalPlan`. We can use this to know whether a plan is generational or not. If it is, we can further invoke methods about the generational plan.
* Add `GCTriggerPolicy::on_gc_release()` which is called in the `Release` work packet. A `GCTriggerPolicy` can use this to get stats before we reclaim memory (e.g. to get promoted size).
* Add an implementation of mem balancer to replace the current simple resize policy.
* Add some logging to help debug GC triggering.

Author: qinsoon

src/plan/generational/barrier.rs

@@ -13,21 +13,21 @@ use crate::MMTK;
 use super::gc_work::GenNurseryProcessEdges;
 use super::gc_work::ProcessModBuf;
 use super::gc_work::ProcessRegionModBuf;
-use super::global::Gen;
+use super::global::CommonGenPlan;
 
 pub struct GenObjectBarrierSemantics<VM: VMBinding> {
     /// MMTk instance
     mmtk: &'static MMTK<VM>,
     /// Generational plan
-    gen: &'static Gen<VM>,
+    gen: &'static CommonGenPlan<VM>,
     /// Object modbuf. Contains a list of objects that may contain pointers to the nursery space.
     modbuf: VectorQueue<ObjectReference>,
     /// Array-copy modbuf. Contains a list of sub-arrays or array slices that may contain pointers to the nursery space.
     region_modbuf: VectorQueue<VM::VMMemorySlice>,
 }
 
 impl<VM: VMBinding> GenObjectBarrierSemantics<VM> {
-    pub fn new(mmtk: &'static MMTK<VM>, gen: &'static Gen<VM>) -> Self {
+    pub fn new(mmtk: &'static MMTK<VM>, gen: &'static CommonGenPlan<VM>) -> Self {
         Self {
             mmtk,
             gen,

src/plan/generational/copying/global.rs

@@ -1,7 +1,8 @@
 use super::gc_work::GenCopyGCWorkContext;
 use super::gc_work::GenCopyNurseryGCWorkContext;
 use super::mutator::ALLOCATOR_MAPPING;
-use crate::plan::generational::global::Gen;
+use crate::plan::generational::global::CommonGenPlan;
+use crate::plan::generational::global::GenerationalPlan;
 use crate::plan::global::BasePlan;
 use crate::plan::global::CommonPlan;
 use crate::plan::global::CreateGeneralPlanArgs;
@@ -27,7 +28,7 @@ use mmtk_macros::PlanTraceObject;
 #[derive(PlanTraceObject)]
 pub struct GenCopy<VM: VMBinding> {
     #[fallback_trace]
-    pub gen: Gen<VM>,
+    pub gen: CommonGenPlan<VM>,
     pub hi: AtomicBool,
     #[trace(CopySemantics::Mature)]
     pub copyspace0: CopySpace<VM>,
@@ -98,7 +99,7 @@ impl<VM: VMBinding> Plan for GenCopy<VM> {
     }
 
     fn prepare(&mut self, tls: VMWorkerThread) {
-        let full_heap = !self.is_current_gc_nursery();
+        let full_heap = !self.gen.is_current_gc_nursery();
         self.gen.prepare(tls);
         if full_heap {
             self.hi
@@ -118,7 +119,7 @@ impl<VM: VMBinding> Plan for GenCopy<VM> {
     }
 
     fn release(&mut self, tls: VMWorkerThread) {
-        let full_heap = !self.is_current_gc_nursery();
+        let full_heap = !self.gen.is_current_gc_nursery();
         self.gen.release(tls);
         if full_heap {
             self.fromspace().release();
@@ -127,7 +128,7 @@ impl<VM: VMBinding> Plan for GenCopy<VM> {
 
     fn end_of_gc(&mut self, _tls: VMWorkerThread) {
         self.gen
-            .set_next_gc_full_heap(Gen::should_next_gc_be_full_heap(self));
+            .set_next_gc_full_heap(CommonGenPlan::should_next_gc_be_full_heap(self));
     }
 
     fn get_collection_reserved_pages(&self) -> usize {
@@ -147,10 +148,6 @@ impl<VM: VMBinding> Plan for GenCopy<VM> {
             >> 1
     }
 
-    fn get_mature_physical_pages_available(&self) -> usize {
-        self.tospace().available_physical_pages()
-    }
-
     fn base(&self) -> &BasePlan<VM> {
         &self.gen.common.base
     }
@@ -159,12 +156,22 @@ impl<VM: VMBinding> Plan for GenCopy<VM> {
         &self.gen.common
     }
 
-    fn generational(&self) -> &Gen<VM> {
+    fn generational(&self) -> Option<&dyn GenerationalPlan<VM = Self::VM>> {
+        Some(self)
+    }
+}
+
+impl<VM: VMBinding> GenerationalPlan for GenCopy<VM> {
+    fn common_gen(&self) -> &CommonGenPlan<Self::VM> {
         &self.gen
     }
 
-    fn is_current_gc_nursery(&self) -> bool {
-        !self.gen.gc_full_heap.load(Ordering::SeqCst)
+    fn get_mature_physical_pages_available(&self) -> usize {
+        self.tospace().available_physical_pages()
+    }
+
+    fn get_mature_reserved_pages(&self) -> usize {
+        self.tospace().reserved_pages()
     }
 }
 
@@ -187,7 +194,7 @@ impl<VM: VMBinding> GenCopy<VM> {
         );
 
         let res = GenCopy {
-            gen: Gen::new(plan_args),
+            gen: CommonGenPlan::new(plan_args),
             hi: AtomicBool::new(false),
             copyspace0,
             copyspace1,

src/plan/generational/gc_work.rs

@@ -1,6 +1,6 @@
 use atomic::Ordering;
 
-use crate::plan::generational::global::Gen;
+use crate::plan::generational::global::CommonGenPlan;
 use crate::policy::space::Space;
 use crate::scheduler::{gc_work::*, GCWork, GCWorker};
 use crate::util::ObjectReference;
@@ -14,7 +14,7 @@ use std::ops::{Deref, DerefMut};
 /// [`crate::scheduler::gc_work::SFTProcessEdges`]. If a plan uses `SFTProcessEdges`,
 /// it does not need to use this type.
 pub struct GenNurseryProcessEdges<VM: VMBinding> {
-    gen: &'static Gen<VM>,
+    gen: &'static CommonGenPlan<VM>,
     base: ProcessEdgesBase<VM>,
 }
 
@@ -24,7 +24,7 @@ impl<VM: VMBinding> ProcessEdgesWork for GenNurseryProcessEdges<VM> {
 
     fn new(edges: Vec<EdgeOf<Self>>, roots: bool, mmtk: &'static MMTK<VM>) -> Self {
         let base = ProcessEdgesBase::new(edges, roots, mmtk);
-        let gen = base.plan().generational();
+        let gen = base.plan().generational().unwrap().common_gen();
         Self { gen, base }
     }
     #[inline]
@@ -95,7 +95,13 @@ impl<E: ProcessEdgesWork> GCWork<E::VM> for ProcessModBuf<E> {
             );
         }
         // scan modbuf only if the current GC is a nursery GC
-        if mmtk.plan.is_current_gc_nursery() {
+        if mmtk
+            .plan
+            .generational()
+            .unwrap()
+            .common_gen()
+            .is_current_gc_nursery()
+        {
             // Scan objects in the modbuf and forward pointers
             let modbuf = std::mem::take(&mut self.modbuf);
             GCWork::do_work(
@@ -129,7 +135,13 @@ impl<E: ProcessEdgesWork> GCWork<E::VM> for ProcessRegionModBuf<E> {
     #[inline(always)]
     fn do_work(&mut self, worker: &mut GCWorker<E::VM>, mmtk: &'static MMTK<E::VM>) {
         // Scan modbuf only if the current GC is a nursery GC
-        if mmtk.plan.is_current_gc_nursery() {
+        if mmtk
+            .plan
+            .generational()
+            .unwrap()
+            .common_gen()
+            .is_current_gc_nursery()
+        {
             // Collect all the entries in all the slices
             let mut edges = vec![];
             for slice in &self.modbuf {

src/plan/generational/global.rs

@@ -5,7 +5,6 @@ use crate::plan::Plan;
 use crate::policy::copyspace::CopySpace;
 use crate::policy::space::Space;
 use crate::scheduler::*;
-use crate::util::conversions;
 use crate::util::copy::CopySemantics;
 use crate::util::heap::VMRequest;
 use crate::util::metadata::side_metadata::SideMetadataSanity;
@@ -22,7 +21,7 @@ use mmtk_macros::PlanTraceObject;
 /// Common implementation for generational plans. Each generational plan
 /// should include this type, and forward calls to it where possible.
 #[derive(PlanTraceObject)]
-pub struct Gen<VM: VMBinding> {
+pub struct CommonGenPlan<VM: VMBinding> {
     /// The nursery space.
     #[trace(CopySemantics::PromoteToMature)]
     pub nursery: CopySpace<VM>,
@@ -36,21 +35,21 @@ pub struct Gen<VM: VMBinding> {
     pub full_heap_gc_count: Arc<Mutex<EventCounter>>,
 }
 
-impl<VM: VMBinding> Gen<VM> {
+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(), false),
+                VMRequest::fixed_extent(args.global_args.options.get_max_nursery_bytes(), false),
             ),
             true,
         );
         let common = CommonPlan::new(args);
 
         let full_heap_gc_count = common.base.stats.new_event_counter("majorGC", true, true);
 
-        Gen {
+        CommonGenPlan {
             nursery,
             common,
             gc_full_heap: AtomicBool::default(),
@@ -97,28 +96,35 @@ impl<VM: VMBinding> Gen<VM> {
     ///
     /// Returns `true` if the nursery has grown to the extent that it may not be able to be copied
     /// into the mature space.
-    fn virtual_memory_exhausted<P: Plan>(&self, plan: &P) -> bool {
+    fn virtual_memory_exhausted(plan: &dyn GenerationalPlan<VM = VM>) -> bool {
         ((plan.get_collection_reserved_pages() as f64
             * VM::VMObjectModel::VM_WORST_CASE_COPY_EXPANSION) as usize)
             > plan.get_mature_physical_pages_available()
     }
 
     /// Check if we need a GC based on the nursery space usage. This method may mark
     /// the following GC as a full heap GC.
-    pub fn collection_required<P: Plan>(
+    pub fn collection_required<P: Plan<VM = VM>>(
         &self,
         plan: &P,
         space_full: bool,
         space: Option<&dyn Space<VM>>,
     ) -> bool {
-        let nursery_full = self.nursery.reserved_pages()
-            >= (conversions::bytes_to_pages_up(self.common.base.options.get_max_nursery()));
+        let cur_nursery = self.nursery.reserved_pages();
+        let max_nursery = self.common.base.options.get_max_nursery_pages();
+        let nursery_full = cur_nursery >= max_nursery;
+        trace!(
+            "nursery_full = {:?} (nursery = {}, max_nursery = {})",
+            nursery_full,
+            cur_nursery,
+            max_nursery,
+        );
 
         if nursery_full {
             return true;
         }
 
-        if self.virtual_memory_exhausted(plan) {
+        if Self::virtual_memory_exhausted(plan.generational().unwrap()) {
             return true;
         }
 
@@ -146,11 +152,12 @@ impl<VM: VMBinding> Gen<VM> {
 
     /// Check if we should do a full heap GC. It returns true if we should have a full heap GC.
     /// It also sets gc_full_heap based on the result.
-    pub fn requires_full_heap_collection<P: Plan>(&self, plan: &P) -> bool {
+    pub fn requires_full_heap_collection<P: Plan<VM = VM>>(&self, plan: &P) -> bool {
         // Allow the same 'true' block for if-else.
         // The conditions are complex, and it is easier to read if we put them to separate if blocks.
         #[allow(clippy::if_same_then_else, clippy::needless_bool)]
         let is_full_heap = if crate::plan::generational::FULL_NURSERY_GC {
+            trace!("full heap: forced full heap");
             // For barrier overhead measurements, we always do full gc in nursery collections.
             true
         } else if self
@@ -160,6 +167,7 @@ impl<VM: VMBinding> Gen<VM> {
             .load(Ordering::SeqCst)
             && *self.common.base.options.full_heap_system_gc
         {
+            trace!("full heap: user triggered");
             // User triggered collection, and we force full heap for user triggered collection
             true
         } else if self.next_gc_full_heap.load(Ordering::SeqCst)
@@ -170,9 +178,18 @@ impl<VM: VMBinding> Gen<VM> {
                 .load(Ordering::SeqCst)
                 > 1
         {
+            trace!(
+                "full heap: next_gc_full_heap = {}, cur_collection_attempts = {}",
+                self.next_gc_full_heap.load(Ordering::SeqCst),
+                self.common
+                    .base
+                    .cur_collection_attempts
+                    .load(Ordering::SeqCst)
+            );
             // Forces full heap collection
             true
-        } else if self.virtual_memory_exhausted(plan) {
+        } else if Self::virtual_memory_exhausted(plan.generational().unwrap()) {
+            trace!("full heap: virtual memory exhausted");
             true
         } else {
             // We use an Appel-style nursery. The default GC (even for a "heap-full" collection)
@@ -250,8 +267,16 @@ impl<VM: VMBinding> Gen<VM> {
     /// [`get_available_pages`](crate::plan::Plan::get_available_pages)
     /// whose value depends on which spaces have been released.
     pub fn should_next_gc_be_full_heap(plan: &dyn Plan<VM = VM>) -> bool {
-        plan.get_available_pages()
-            < conversions::bytes_to_pages_up(plan.base().options.get_min_nursery())
+        let available = plan.get_available_pages();
+        let min_nursery = plan.base().options.get_min_nursery_pages();
+        let next_gc_full_heap = available < min_nursery;
+        trace!(
+            "next gc will be full heap? {}, availabe pages = {}, min nursery = {}",
+            next_gc_full_heap,
+            available,
+            min_nursery
+        );
+        next_gc_full_heap
     }
 
     /// Set next_gc_full_heap to the given value.
@@ -272,3 +297,22 @@ impl<VM: VMBinding> Gen<VM> {
         self.nursery.reserved_pages() + self.common.get_used_pages()
     }
 }
+
+/// This trait include methods that are specific to generational plans.
+pub trait GenerationalPlan: Plan {
+    /// Return the common generational implementation [`crate::plan::generational::global::CommonGenPlan`].
+    fn common_gen(&self) -> &CommonGenPlan<Self::VM>;
+
+    /// Return the number of pages available for allocation into the mature space.
+    fn get_mature_physical_pages_available(&self) -> usize;
+
+    /// Return the number of used pages in the mature space.
+    fn get_mature_reserved_pages(&self) -> usize;
+}
+
+/// Is current GC only collecting objects allocated since last GC? This method can be called
+/// with any plan (generational or not). For non generational plans, it will always return false.
+pub fn is_nursery_gc<VM: VMBinding>(plan: &dyn Plan<VM = VM>) -> bool {
+    plan.generational()
+        .map_or(false, |plan| plan.common_gen().is_current_gc_nursery())
+}