Bug 1640844 - Part 5: Take account of how much time we spend collecting when calculating nursery size r=sfink

This adds a goal of using less then 1% of total time collecthing the nursery, which has the effect of increasing the nursery size where a lot of nursery garbage is created but little is tenured.

In local testing this is a win on ARES6 and octane, but perfherder paints a more ambiguous picture.  I'd like to land this anyway and we can back it out if it causes problems.

Differential Revision: https://phabricator.services.mozilla.com/D80003

js/src/gc/Nursery.cpp

@@ -1557,10 +1557,22 @@ size_t js::Nursery::targetSize(JSGCInvocationKind kind, JS::GCReason reason) {
   double fractionPromoted =
       double(previousGC.tenuredBytes) / double(previousGC.nurseryCapacity);
 
-  // Adjust the nursery size to try to achieve a target promotion rate.
-  static const double PromotionGoal = 0.02;
+  // Calculate the fraction of time spent collecting the nursery.
+  double timeFraction = 0.0;
+#ifndef JS_MORE_DETERMINISTIC
+  if (lastResizeTime) {
+    TimeDuration collectorTime = now - collectionStartTime();
+    TimeDuration totalTime = now - lastResizeTime;
+    timeFraction = collectorTime.ToSeconds() / totalTime.ToSeconds();
+  }
+#endif
 
-  double growthFactor = fractionPromoted / PromotionGoal;
+  // Adjust the nursery size to try to achieve a target promotion rate and
+  // collector time goals.
+  static const double PromotionGoal = 0.02;
+  static const double TimeGoal = 0.01;
+  double growthFactor =
+      std::max(fractionPromoted / PromotionGoal, timeFraction / TimeGoal);
 
   // Limit the range of the growth factor to prevent transient high promotion
   // rates from affecting the nursery size too far into the future.
@@ -1574,6 +1586,7 @@ size_t js::Nursery::targetSize(JSGCInvocationKind kind, JS::GCReason reason) {
       now - lastResizeTime < TimeDuration::FromMilliseconds(200)) {
     growthFactor = 0.75 * smoothedGrowthFactor + 0.25 * growthFactor;
   }
+
   lastResizeTime = now;
   smoothedGrowthFactor = growthFactor;
 #endif

js/src/gc/Nursery.h

@@ -426,6 +426,10 @@ class Nursery {
 
   void joinDecommitTask() { decommitTask.join(); }
 
+  mozilla::TimeStamp collectionStartTime() {
+    return startTimes_[ProfileKey::Total];
+  }
+
   // Round a size in bytes to the nearest valid nursery size.
   static size_t roundSize(size_t size);