Bug 723350 - Improve last-ditch GC trigger. r=billm

js/src/jsapi.cpp

@@ -757,7 +757,6 @@ JSRuntime::JSRuntime()
     gcCallback(NULL),
     gcSliceCallback(NULL),
     gcFinalizeCallback(NULL),
-    gcMallocBytes(0),
     gcBlackRootsTraceOp(NULL),
     gcBlackRootsData(NULL),
     gcGrayRootsTraceOp(NULL),

js/src/jscntxt.cpp

@@ -1102,22 +1102,10 @@ JSContext::runningWithTrustedPrincipals() const
 void
 JSRuntime::updateMallocCounter(JSContext *cx, size_t nbytes)
 {
-    /* We tolerate any thread races when updating gcMallocBytes. */
-    ptrdiff_t oldCount = gcMallocBytes;
-    ptrdiff_t newCount = oldCount - ptrdiff_t(nbytes);
-    gcMallocBytes = newCount;
-    if (JS_UNLIKELY(newCount <= 0 && oldCount > 0))
-        onTooMuchMalloc();
-    else if (cx && cx->compartment)
+    if (cx && cx->compartment)
         cx->compartment->updateMallocCounter(nbytes);
 }
 
-JS_FRIEND_API(void)
-JSRuntime::onTooMuchMalloc()
-{
-    TriggerGC(this, gcreason::TOO_MUCH_MALLOC);
-}
-
 JS_FRIEND_API(void *)
 JSRuntime::onOutOfMemory(void *p, size_t nbytes, JSContext *cx)
 {

js/src/jscntxt.h

@@ -644,13 +644,6 @@ struct JSRuntime : js::RuntimeFriendFields
     js::GCSliceCallback gcSliceCallback;
     JSFinalizeCallback  gcFinalizeCallback;
 
-  private:
-    /*
-     * Malloc counter to measure memory pressure for GC scheduling. It runs
-     * from gcMaxMallocBytes down to zero.
-     */
-    volatile ptrdiff_t  gcMallocBytes;
-
   public:
     /*
      * The trace operations to trace embedding-specific GC roots. One is for
@@ -855,17 +848,8 @@ struct JSRuntime : js::RuntimeFriendFields
     JS_DECLARE_NEW_METHODS(malloc_, JS_ALWAYS_INLINE)
     JS_DECLARE_DELETE_METHODS(free_, JS_ALWAYS_INLINE)
 
-    bool isGCMallocLimitReached() const { return gcMallocBytes <= 0; }
-
-    void resetGCMallocBytes() { gcMallocBytes = ptrdiff_t(gcMaxMallocBytes); }
-
     void setGCMaxMallocBytes(size_t value) {
-        /*
-         * For compatibility treat any value that exceeds PTRDIFF_T_MAX to
-         * mean that value.
-         */
-        gcMaxMallocBytes = (ptrdiff_t(value) >= 0) ? value : size_t(-1) >> 1;
-        resetGCMallocBytes();
+        gcMaxMallocBytes = value;
     }
 
     /*
@@ -877,12 +861,6 @@ struct JSRuntime : js::RuntimeFriendFields
      * the caller must ensure that no deadlock possible during OOM reporting.
      */
     void updateMallocCounter(JSContext *cx, size_t nbytes);
-
-    /*
-     * The function must be called outside the GC lock.
-     */
-    JS_FRIEND_API(void) onTooMuchMalloc();
-
     /*
      * This should be called after system malloc/realloc returns NULL to try
      * to recove some memory or to report an error. Failures in malloc and

js/src/jscompartment.cpp

@@ -535,17 +535,13 @@ JSCompartment::purge()
 void
 JSCompartment::resetGCMallocBytes()
 {
-    gcMallocBytes = ptrdiff_t(gcMaxMallocBytes);
+    gcMallocBytes = gcMaxMallocBytes;
 }
 
 void
 JSCompartment::setGCMaxMallocBytes(size_t value)
 {
-    /*
-     * For compatibility treat any value that exceeds PTRDIFF_T_MAX to
-     * mean that value.
-     */
-    gcMaxMallocBytes = (ptrdiff_t(value) >= 0) ? value : size_t(-1) >> 1;
+    gcMaxMallocBytes = value;
     resetGCMallocBytes();
 }
 

js/src/jscompartment.h

@@ -178,7 +178,6 @@ struct JSCompartment
 
     size_t                       gcBytes;
     size_t                       gcTriggerBytes;
-    size_t                       gcMaxMallocBytes;
 
     bool                         hold;
     bool                         isSystemCompartment;
@@ -245,7 +244,8 @@ struct JSCompartment
      * gcMaxMallocBytes down to zero. This counter should be used only when it's
      * not possible to know the size of a free.
      */
-    ptrdiff_t                    gcMallocBytes;
+    size_t                       gcMallocBytes;
+    size_t                       gcMaxMallocBytes;
 
     enum { DebugFromC = 1, DebugFromJS = 2 };
 
@@ -281,13 +281,19 @@ struct JSCompartment
     void resetGCMallocBytes();
     void setGCMaxMallocBytes(size_t value);
     void updateMallocCounter(size_t nbytes) {
-        ptrdiff_t oldCount = gcMallocBytes;
-        ptrdiff_t newCount = oldCount - ptrdiff_t(nbytes);
+        size_t oldCount = gcMallocBytes;
+        size_t newCount = oldCount - nbytes;
         gcMallocBytes = newCount;
-        if (JS_UNLIKELY(newCount <= 0 && oldCount > 0))
+        // gcMallocBytes will wrap around and be bigger than gcMaxAllocBytes if a signed value
+        // would be < 0
+        if (JS_UNLIKELY(oldCount <= gcMaxMallocBytes && newCount > gcMaxMallocBytes))
             onTooMuchMalloc();
     }
 
+    bool isTooMuchMalloc() const {
+        return gcMallocBytes > gcMaxMallocBytes;
+     }
+
     void onTooMuchMalloc();
 
     void mallocInCompartment(size_t nbytes) {

js/src/jsgc.cpp

@@ -1666,7 +1666,8 @@ ArenaLists::refillFreeList(JSContext *cx, AllocKind thingKind)
     JSRuntime *rt = comp->rt;
     JS_ASSERT(!rt->gcRunning);
 
-    bool runGC = rt->gcIncrementalState != NO_INCREMENTAL && comp->gcBytes > comp->gcTriggerBytes;
+    bool runGC = rt->gcIncrementalState != NO_INCREMENTAL &&
+            (comp->gcBytes > comp->gcTriggerBytes || comp->isTooMuchMalloc());
     for (;;) {
         if (JS_UNLIKELY(runGC)) {
             PrepareCompartmentForGC(comp);
@@ -3308,8 +3309,6 @@ AutoGCSession::AutoGCSession(JSRuntime *rt)
 
     runtime->gcNumber++;
 
-    runtime->resetGCMallocBytes();
-
     /* Clear gcMallocBytes for all compartments */
     for (CompartmentsIter c(runtime); !c.done(); c.next())
         c->resetGCMallocBytes();