Bug 1133759 - Always shrink GC buffers at the end of a shrinking GC r=terrence

dom/base/nsJSEnvironment.cpp

@@ -2204,8 +2204,11 @@ DOMGCSliceCallback(JSRuntime *aRt, JS::GCProgress aProgress, const JS::GCDescrip
         nsJSContext::KillFullGCTimer();
 
         // Avoid shrinking during heavy activity, which is suggested by
-        // compartment GC.
-        nsJSContext::PokeShrinkGCBuffers();
+        // compartment GC. We don't need to shrink after a shrinking GC as this
+        // happens automatically in this case.
+        if (aDesc.invocationKind_ == GC_NORMAL) {
+          nsJSContext::PokeShrinkGCBuffers();
+        }
       }
 
       if (ShouldTriggerCC(nsCycleCollector_suspectedCount())) {

js/public/GCAPI.h

@@ -263,9 +263,10 @@ enum GCProgress {
 
 struct JS_PUBLIC_API(GCDescription) {
     bool isCompartment_;
+    JSGCInvocationKind invocationKind_;
 
-    explicit GCDescription(bool isCompartment)
-      : isCompartment_(isCompartment) {}
+    GCDescription(bool isCompartment, JSGCInvocationKind kind)
+      : isCompartment_(isCompartment), invocationKind_(kind) {}
 
     char16_t *formatMessage(JSRuntime *rt) const;
     char16_t *formatJSON(JSRuntime *rt, uint64_t timestamp) const;

js/src/gc/Statistics.cpp

@@ -1005,7 +1005,7 @@ Statistics::beginSlice(const ZoneGCStats &zoneStats, JSGCInvocationKind gckind,
         bool wasFullGC = zoneStats.isCollectingAllZones();
         if (sliceCallback)
             (*sliceCallback)(runtime, first ? JS::GC_CYCLE_BEGIN : JS::GC_SLICE_BEGIN,
-                             JS::GCDescription(!wasFullGC));
+                             JS::GCDescription(!wasFullGC, gckind));
     }
 }
 
@@ -1029,7 +1029,7 @@ Statistics::endSlice()
         bool wasFullGC = zoneStats.isCollectingAllZones();
         if (sliceCallback)
             (*sliceCallback)(runtime, last ? JS::GC_CYCLE_END : JS::GC_SLICE_END,
-                             JS::GCDescription(!wasFullGC));
+                             JS::GCDescription(!wasFullGC, gckind));
     }
 
     /* Do this after the slice callback since it uses these values. */

js/src/jsgc.cpp

@@ -5463,6 +5463,10 @@ GCRuntime::compactPhase(bool lastGC)
         releaseRelocatedArenas(relocatedList);
 #endif
 
+    // Ensure execess chunks are returns to the system and free arenas
+    // decommitted.
+    shrinkBuffers();
+
 #ifdef DEBUG
     CheckHashTablesAfterMovingGC(rt);
     for (GCZonesIter zone(rt); !zone.done(); zone.next()) {
@@ -6303,6 +6307,7 @@ js::PrepareForDebugGC(JSRuntime *rt)
 JS_PUBLIC_API(void)
 JS::ShrinkGCBuffers(JSRuntime *rt)
 {
+    MOZ_ASSERT(!rt->isHeapBusy());
     rt->gc.shrinkBuffers();
 }
 
@@ -6311,7 +6316,6 @@ GCRuntime::shrinkBuffers()
 {
     AutoLockHelperThreadState helperLock;
     AutoLockGC lock(rt);
-    MOZ_ASSERT(!rt->isHeapBusy());
 
     if (CanUseExtraThreads())
         helperState.startBackgroundShrink(lock);