Bug 1296639 - Remove SpiderMonkey's periodic full GC r=sfink

js/public/GCAPI.h

@@ -65,7 +65,7 @@ namespace JS {
     D(EVICT_NURSERY)                            \
     D(FULL_STORE_BUFFER)                        \
     D(SHARED_MEMORY_LIMIT)                      \
-    D(PERIODIC_FULL_GC)                         \
+    D(UNUSED1)                                  \
     D(INCREMENTAL_TOO_SLOW)                     \
     D(ABORT_GC)                                 \
                                                 \

js/src/gc/GCRuntime.h

@@ -459,14 +459,6 @@ class GCSchedulingTunables
  *            -> Responsiveness is proportional to t[marking] + t[sweeping].
  *            -> size[retained] is proportional only to GC allocations.
  *
- *      PERIODIC_FULL_GC
- *      ----------------
- *      When we return to the event loop and it has been 20 seconds since we've
- *      done a GC, we start an incremenal, all-zones, shrinking GC.
- *
- *          Assumptions:
- *            -> Our triggers are incomplete.
- *
  *      ALLOC_TRIGGER (non-incremental)
  *      -------------------------------
  *      If we do not return to the event loop before getting all the way to our
@@ -623,8 +615,7 @@ class GCRuntime
     void maybeAllocTriggerZoneGC(Zone* zone, const AutoLockGC& lock);
     // The return value indicates if we were able to do the GC.
     bool triggerZoneGC(Zone* zone, JS::gcreason::Reason reason);
-    MOZ_MUST_USE bool maybeGC(Zone* zone);
-    void maybePeriodicFullGC();
+    void maybeGC(Zone* zone);
     void minorGC(JS::gcreason::Reason reason,
                  gcstats::Phase phase = gcstats::PHASE_MINOR_GC) JS_HAZ_GC_CALL;
     void evictNursery(JS::gcreason::Reason reason = JS::gcreason::EVICT_NURSERY) {
@@ -1072,7 +1063,6 @@ class GCRuntime
 
   private:
     bool chunkAllocationSinceLastGC;
-    int64_t nextFullGCTime;
     int64_t lastGCTime;
 
     JSGCMode mode;

js/src/jsapi.cpp

@@ -1339,8 +1339,7 @@ JS_PUBLIC_API(void)
 JS_MaybeGC(JSContext* cx)
 {
     GCRuntime& gc = cx->runtime()->gc;
-    if (!gc.maybeGC(cx->zone()))
-        gc.maybePeriodicFullGC();
+    gc.maybeGC(cx->zone());
 }
 
 JS_PUBLIC_API(void)

js/src/jsgc.cpp

@@ -249,9 +249,6 @@ using mozilla::Swap;
 
 using JS::AutoGCRooter;
 
-/* Perform a Full GC every 20 seconds if MaybeGC is called */
-static const uint64_t GC_IDLE_FULL_SPAN = 20 * 1000 * 1000;
-
 /* Increase the IGC marking slice time if we are in highFrequencyGC mode. */
 static const int IGC_MARK_SLICE_MULTIPLIER = 2;
 
@@ -807,7 +804,6 @@ GCRuntime::GCRuntime(JSRuntime* rt) :
     numArenasFreeCommitted(0),
     verifyPreData(nullptr),
     chunkAllocationSinceLastGC(false),
-    nextFullGCTime(0),
     lastGCTime(PRMJ_Now()),
     mode(JSGC_MODE_INCREMENTAL),
     numActiveZoneIters(0),
@@ -3039,7 +3035,7 @@ GCRuntime::triggerZoneGC(Zone* zone, JS::gcreason::Reason reason)
     return true;
 }
 
-bool
+void
 GCRuntime::maybeGC(Zone* zone)
 {
     MOZ_ASSERT(CurrentThreadCanAccessRuntime(rt));
@@ -3048,12 +3044,12 @@ GCRuntime::maybeGC(Zone* zone)
     if (hasZealMode(ZealMode::Alloc) || hasZealMode(ZealMode::Poke)) {
         JS::PrepareForFullGC(rt->contextFromMainThread());
         gc(GC_NORMAL, JS::gcreason::DEBUG_GC);
-        return true;
+        return;
     }
 #endif
 
     if (gcIfRequested())
-        return true;
+        return;
 
     if (zone->usage.gcBytes() > 1024 * 1024 &&
         zone->usage.gcBytes() >= zone->threshold.allocTrigger(schedulingState.inHighFrequencyGCMode()) &&
@@ -3062,37 +3058,7 @@ GCRuntime::maybeGC(Zone* zone)
     {
         PrepareZoneForGC(zone);
         startGC(GC_NORMAL, JS::gcreason::EAGER_ALLOC_TRIGGER);
-        return true;
     }
-
-    return false;
-}
-
-void
-GCRuntime::maybePeriodicFullGC()
-{
-    /*
-     * Trigger a periodic full GC.
-     *
-     * This is a source of non-determinism, but is not called from the shell.
-     *
-     * Access to the counters and, on 32 bit, setting gcNextFullGCTime below
-     * is not atomic and a race condition could trigger or suppress the GC. We
-     * tolerate this.
-     */
-#ifndef JS_MORE_DETERMINISTIC
-    int64_t now = PRMJ_Now();
-    if (nextFullGCTime && nextFullGCTime <= now && !isIncrementalGCInProgress()) {
-        if (chunkAllocationSinceLastGC ||
-            numArenasFreeCommitted > decommitThreshold)
-        {
-            JS::PrepareForFullGC(rt->contextFromMainThread());
-            startGC(GC_SHRINK, JS::gcreason::PERIODIC_FULL_GC);
-        } else {
-            nextFullGCTime = now + GC_IDLE_FULL_SPAN;
-        }
-    }
-#endif
 }
 
 // Do all possible decommit immediately from the current thread without
@@ -6141,10 +6107,6 @@ GCRuntime::gcCycle(bool nonincrementalByAPI, SliceBudget& budget, JS::gcreason::
 
     incrementalCollectSlice(budget, reason, session.lock);
 
-#ifndef JS_MORE_DETERMINISTIC
-    nextFullGCTime = PRMJ_Now() + GC_IDLE_FULL_SPAN;
-#endif
-
     chunkAllocationSinceLastGC = false;
 
 #ifdef JS_GC_ZEAL