Bug 1458154 - Add a tunable for idle nursery collection r=jonco

--HG--
extra : source : c5b1eae8a19756f85b8b059bff4bb1b4b8ab7c90
extra : amend_source : e1b38bbadd6d62efd22e754e752b064d175193ec

js/public/GCAPI.h

@@ -256,6 +256,15 @@ typedef enum JSGCParamKey {
      * Pref: None
      */
     JSGC_ALLOCATION_THRESHOLD_FACTOR_AVOID_INTERRUPT = 26,
+
+    /**
+     * Attempt to run a minor GC in the idle time if the free space falls
+     * below this threshold.
+     *
+     * Default: NurseryChunkUsableSize / 4
+     * Pref: None
+     */
+    JSGC_NURSERY_FREE_THRESHOLD_FOR_IDLE_COLLECTION = 27,
 } JSGCParamKey;
 
 /*

js/src/gc/GC.cpp

@@ -336,6 +336,10 @@ namespace TuningDefaults {
     /* JSGC_COMPACTING_ENABLED */
     static const bool CompactingEnabled = true;
 
+    /* JSGC_NURSERY_FREE_THRESHOLD_FOR_IDLE_COLLECTION */
+    static const uint32_t NurseryFreeThresholdForIdleCollection =
+        Nursery::NurseryChunkUsableSize / 4;
+
 }}} // namespace js::gc::TuningDefaults
 
 /*
@@ -1479,6 +1483,11 @@ GCSchedulingTunables::setParameter(JSGCParamKey key, uint32_t value, const AutoL
       case JSGC_MAX_EMPTY_CHUNK_COUNT:
         setMaxEmptyChunkCount(value);
         break;
+      case JSGC_NURSERY_FREE_THRESHOLD_FOR_IDLE_COLLECTION:
+        if (value > gcMaxNurseryBytes())
+            value = gcMaxNurseryBytes();
+        nurseryFreeThresholdForIdleCollection_ = value;
+        break;
       default:
         MOZ_CRASH("Unknown GC parameter.");
     }
@@ -1572,7 +1581,8 @@ GCSchedulingTunables::GCSchedulingTunables()
     lowFrequencyHeapGrowth_(TuningDefaults::LowFrequencyHeapGrowth),
     dynamicMarkSliceEnabled_(TuningDefaults::DynamicMarkSliceEnabled),
     minEmptyChunkCount_(TuningDefaults::MinEmptyChunkCount),
-    maxEmptyChunkCount_(TuningDefaults::MaxEmptyChunkCount)
+    maxEmptyChunkCount_(TuningDefaults::MaxEmptyChunkCount),
+    nurseryFreeThresholdForIdleCollection_(TuningDefaults::NurseryFreeThresholdForIdleCollection)
 {}
 
 void
@@ -1653,6 +1663,10 @@ GCSchedulingTunables::resetParameter(JSGCParamKey key, const AutoLockGC& lock)
       case JSGC_MAX_EMPTY_CHUNK_COUNT:
         setMaxEmptyChunkCount(TuningDefaults::MaxEmptyChunkCount);
         break;
+      case JSGC_NURSERY_FREE_THRESHOLD_FOR_IDLE_COLLECTION:
+        nurseryFreeThresholdForIdleCollection_ =
+            TuningDefaults::NurseryFreeThresholdForIdleCollection;
+        break;
       default:
         MOZ_CRASH("Unknown GC parameter.");
     }

js/src/gc/Nursery.cpp

@@ -676,6 +676,13 @@ js::Nursery::endProfile(ProfileKey key)
     totalDurations_[key] += profileDurations_[key];
 }
 
+bool
+js::Nursery::needIdleTimeCollection() const {
+    uint32_t threshold =
+        runtime()->gc.tunables.nurseryFreeThresholdForIdleCollection();
+    return minorGCRequested() || freeSpace() < threshold;
+}
+
 static inline bool
 IsFullStoreBufferReason(JS::gcreason::Reason reason)
 {

js/src/gc/Nursery.h

@@ -333,20 +333,14 @@ class Nursery
     JS::gcreason::Reason minorGCTriggerReason() const { return minorGCTriggerReason_; }
     void clearMinorGCRequest() { minorGCTriggerReason_ = JS::gcreason::NO_REASON; }
 
-    bool needIdleTimeCollection() const {
-        return minorGCRequested() ||
-               (freeSpace() < kIdleTimeCollectionThreshold);
-    }
+    bool needIdleTimeCollection() const;
 
     bool enableProfiling() const { return enableProfiling_; }
 
-  private:
     /* The amount of space in the mapped nursery available to allocations. */
     static const size_t NurseryChunkUsableSize = gc::ChunkSize - gc::ChunkTrailerSize;
 
-    /* Attemp to run a minor GC in the idle time if the free space falls below this threshold. */
-    static constexpr size_t kIdleTimeCollectionThreshold = NurseryChunkUsableSize / 4;
-
+  private:
     JSRuntime* runtime_;
 
     /* Vector of allocated chunks to allocate from. */

js/src/gc/Scheduling.h

@@ -429,6 +429,14 @@ class GCSchedulingTunables
     UnprotectedData<uint32_t> minEmptyChunkCount_;
     UnprotectedData<uint32_t> maxEmptyChunkCount_;
 
+    /*
+     * JSGC_NURSERY_FREE_THRESHOLD_FOR_IDLE_COLLECTION
+     *
+     * Attempt to run a minor GC in the idle time if the free space falls
+     * below this threshold.
+     */
+    UnprotectedData<uint32_t> nurseryFreeThresholdForIdleCollection_;
+
   public:
     GCSchedulingTunables();
 
@@ -449,6 +457,9 @@ class GCSchedulingTunables
     bool isDynamicMarkSliceEnabled() const { return dynamicMarkSliceEnabled_; }
     unsigned minEmptyChunkCount(const AutoLockGC&) const { return minEmptyChunkCount_; }
     unsigned maxEmptyChunkCount() const { return maxEmptyChunkCount_; }
+    uint32_t nurseryFreeThresholdForIdleCollection() const {
+        return nurseryFreeThresholdForIdleCollection_;
+    }
 
     MOZ_MUST_USE bool setParameter(JSGCParamKey key, uint32_t value, const AutoLockGC& lock);
     void resetParameter(JSGCParamKey key, const AutoLockGC& lock);