Bug 1380768 (part 2) - Add a pref for nursery size, r=sfink.

dom/base/nsJSEnvironment.cpp

@@ -2598,8 +2598,18 @@ SetMemoryMaxPrefChangedCallback(const char* aPrefName, void* aClosure)
 {
   int32_t pref = Preferences::GetInt(aPrefName, -1);
   // handle overflow and negative pref values
-  uint32_t max = (pref <= 0 || pref >= 0x1000) ? -1 : (uint32_t)pref * 1024 * 1024;
-  SetGCParameter(JSGC_MAX_BYTES, max);
+  CheckedInt<uint32_t> max = CheckedInt<uint32_t>(pref) * 1024 * 1024;
+  SetGCParameter(JSGC_MAX_BYTES, max.isValid() ? max.value() : -1);
+}
+
+static void
+SetMemoryNurseryMaxPrefChangedCallback(const char* aPrefName, void* aClosure)
+{
+  int32_t pref = Preferences::GetInt(aPrefName, -1);
+  // handle overflow and negative pref values
+  CheckedInt<uint32_t> max = CheckedInt<uint32_t>(pref) * 1024;
+  SetGCParameter(JSGC_MAX_NURSERY_BYTES,
+    max.isValid() ? max.value() : JS::DefaultNurseryBytes);
 }
 
 static void
@@ -2792,6 +2802,8 @@ nsJSContext::EnsureStatics()
 
   Preferences::RegisterCallbackAndCall(SetMemoryMaxPrefChangedCallback,
                                        "javascript.options.mem.max");
+  Preferences::RegisterCallbackAndCall(SetMemoryNurseryMaxPrefChangedCallback,
+                                       "javascript.options.mem.nursery.max_kb");
 
   Preferences::RegisterCallbackAndCall(SetMemoryGCModePrefChangedCallback,
                                        "javascript.options.mem.gc_per_zone");

js/public/HeapAPI.h

@@ -101,7 +101,11 @@ MOZ_ALWAYS_INLINE bool IsInsideNursery(const js::gc::Cell* cell);
 namespace JS {
 struct Zone;
 
-/* Default size for the generational nursery in bytes. */
+/*
+ * Default size for the generational nursery in bytes.
+ * This is the initial nursery size, when running in the browser this is
+ * updated by JS_SetGCParameter().
+ */
 const uint32_t DefaultNurseryBytes = 16 * js::gc::ChunkSize;
 
 /* Default maximum heap size in bytes to pass to JS_NewContext(). */

js/src/gc/GCRuntime.h

@@ -140,7 +140,11 @@ class GCSchedulingTunables
      */
     UnprotectedData<size_t> gcMaxBytes_;
 
-    /* Maximum nursery size for each zone group. */
+    /*
+     * Maximum nursery size for each zone group.
+     * Initially DefaultNurseryBytes and can be set by
+     * javascript.options.mem.nursery.max_kb
+     */
     ActiveThreadData<size_t> gcMaxNurseryBytes_;
 
     /*

js/src/gc/Nursery.cpp

@@ -646,6 +646,11 @@ js::Nursery::collect(JS::gcreason::Reason reason)
     // because gcBytes >= gcMaxBytes.
     if (rt->gc.usage.gcBytes() >= rt->gc.tunables.gcMaxBytes())
         disable();
+    // Disable the nursery if the user changed the configuration setting.  The
+    // nursery can only be re-enabled by resetting the configurationa and
+    // restarting firefox.
+    if (maxNurseryChunks_ == 0)
+        disable();
 
     endProfile(ProfileKey::Total);
     minorGcCount_++;
@@ -924,6 +929,7 @@ js::Nursery::maybeResizeNursery(JS::gcreason::Reason reason, double promotionRat
 {
     static const double GrowThreshold   = 0.05;
     static const double ShrinkThreshold = 0.01;
+    unsigned newMaxNurseryChunks;
 
     // Shrink the nursery to its minimum size of we ran out of memory or
     // received a memory pressure event.
@@ -932,10 +938,30 @@ js::Nursery::maybeResizeNursery(JS::gcreason::Reason reason, double promotionRat
         return;
     }
 
+#ifdef JS_GC_ZEAL
+    // This zeal mode disabled nursery resizing.
+    if (runtime()->hasZealMode(ZealMode::GenerationalGC))
+        return;
+#endif
+
+    newMaxNurseryChunks = runtime()->gc.tunables.gcMaxNurseryBytes() >> ChunkShift;
+    if (newMaxNurseryChunks != maxNurseryChunks_) {
+        maxNurseryChunks_ = newMaxNurseryChunks;
+        /* The configured maximum nursery size is changing */
+        int extraChunks = numChunks() - newMaxNurseryChunks;
+        if (extraChunks > 0) {
+            /* We need to shrink the nursery */
+            shrinkAllocableSpace(extraChunks);
+
+            previousPromotionRate_ = promotionRate;
+            return;
+        }
+    }
+
     if (promotionRate > GrowThreshold)
         growAllocableSpace();
     else if (promotionRate < ShrinkThreshold && previousPromotionRate_ < ShrinkThreshold)
-        shrinkAllocableSpace();
+        shrinkAllocableSpace(1);
 
     previousPromotionRate_ = promotionRate;
 }
@@ -947,13 +973,13 @@ js::Nursery::growAllocableSpace()
 }
 
 void
-js::Nursery::shrinkAllocableSpace()
+js::Nursery::shrinkAllocableSpace(unsigned removeNumChunks)
 {
 #ifdef JS_GC_ZEAL
     if (runtime()->hasZealMode(ZealMode::GenerationalGC))
         return;
 #endif
-    updateNumChunks(Max(numChunks() - 1, 1u));
+    updateNumChunks(Max(numChunks() - removeNumChunks, 1u));
 }
 
 void

js/src/gc/Nursery.h

@@ -468,7 +468,7 @@ class Nursery
     /* Change the allocable space provided by the nursery. */
     void maybeResizeNursery(JS::gcreason::Reason reason, double promotionRate);
     void growAllocableSpace();
-    void shrinkAllocableSpace();
+    void shrinkAllocableSpace(unsigned removeNumChunks);
     void minimizeAllocableSpace();
 
     /* Profile recording and printing. */

modules/libpref/init/all.js

@@ -1436,6 +1436,7 @@ pref("javascript.options.discardSystemSource", false);
 // Comment 32 and Bug 613551.
 pref("javascript.options.mem.high_water_mark", 128);
 pref("javascript.options.mem.max", -1);
+pref("javascript.options.mem.nursery.max_kb", -1);
 pref("javascript.options.mem.gc_per_zone", true);
 pref("javascript.options.mem.gc_incremental", true);
 pref("javascript.options.mem.gc_incremental_slice_ms", 5);