Bug 1787526 - Part 1: Add configuration for semispace nursery r=sfink

Add a GC parameter and pref for semispace nursery which is disabled by default.

Enable it for the shell rootanalysis job to get get some test coverage.

Differential Revision: https://phabricator.services.mozilla.com/D196431

dom/base/nsJSEnvironment.cpp

@@ -2121,6 +2121,13 @@ void nsJSContext::EnsureStatics() {
                                        "javascript.options.mem.gc_compacting",
                                        (void*)JSGC_COMPACTING_ENABLED);
 
+#ifdef NIGHTLY_BUILD
+  Preferences::RegisterCallbackAndCall(
+      SetMemoryPrefChangedCallbackBool,
+      "javascript.options.mem.gc_experimental_semispace_nursery",
+      (void*)JSGC_SEMISPACE_NURSERY_ENABLED);
+#endif
+
   Preferences::RegisterCallbackAndCall(
       SetMemoryPrefChangedCallbackBool,
       "javascript.options.mem.gc_parallel_marking",

dom/workers/RuntimeService.cpp

@@ -372,6 +372,9 @@ void LoadJSGCMemoryOptions(const char* aPrefName, void* /* aClosure */) {
       PREF("gc_parallel_marking", JSGC_PARALLEL_MARKING_ENABLED),
       PREF("gc_parallel_marking_threshold_mb",
            JSGC_PARALLEL_MARKING_THRESHOLD_MB),
+#ifdef NIGHTLY_BUILD
+      PREF("gc_experimental_semispace_nursery", JSGC_SEMISPACE_NURSERY_ENABLED),
+#endif
       // Note: Workers do not currently trigger eager minor GC, but if that is
       // desired the following parameters should be added:
       // javascript.options.mem.nursery_eager_collection_threshold_kb
@@ -426,6 +429,9 @@ void LoadJSGCMemoryOptions(const char* aPrefName, void* /* aClosure */) {
       }
       case JSGC_COMPACTING_ENABLED:
       case JSGC_PARALLEL_MARKING_ENABLED:
+#ifdef NIGHTLY_BUILD
+      case JSGC_SEMISPACE_NURSERY_ENABLED:
+#endif
       case JSGC_BALANCED_HEAP_LIMITS_ENABLED: {
         bool present;
         bool prefValue = GetPref(pref->fullName, false, &present);

js/public/GCAPI.h

@@ -459,6 +459,15 @@ typedef enum JSGCParamKey {
    * Default: ParallelMarkingThresholdMB
    */
   JSGC_PARALLEL_MARKING_THRESHOLD_MB = 50,
+
+  /**
+   * Whether the semispace nursery is enabled.
+   *
+   * Pref: javascript.options.mem.gc_experimental_semispace_nursery
+   * Default: SemispaceNurseryEnabled
+   */
+  JSGC_SEMISPACE_NURSERY_ENABLED = 51,
+
 } JSGCParamKey;
 
 /*

js/src/devtools/automation/variants/rootanalysis

@@ -4,6 +4,6 @@
     "debug": true,
     "env": {
         "JS_GC_ZEAL": "GenerationalGC",
-        "JSTESTS_EXTRA_ARGS": "--jitflags=debug"
+        "JSTESTS_EXTRA_ARGS": "--jitflags=debug --args='--gc-param=semispaceNurseryEnabled=1'"
     }
 }

js/src/gc/GC.cpp

@@ -1073,6 +1073,11 @@ bool GCRuntime::setParameter(JSGCParamKey key, uint32_t value,
         marker->incrementalWeakMapMarkingEnabled = value != 0;
       }
       break;
+    case JSGC_SEMISPACE_NURSERY_ENABLED: {
+      AutoUnlockGC unlock(lock);
+      nursery().setSemispaceEnabled(value);
+      break;
+    }
     case JSGC_MIN_EMPTY_CHUNK_COUNT:
       setMinEmptyChunkCount(value, lock);
       break;
@@ -1160,6 +1165,11 @@ void GCRuntime::resetParameter(JSGCParamKey key, AutoLockGC& lock) {
             TuningDefaults::IncrementalWeakMapMarkingEnabled;
       }
       break;
+    case JSGC_SEMISPACE_NURSERY_ENABLED: {
+      AutoUnlockGC unlock(lock);
+      nursery().setSemispaceEnabled(TuningDefaults::SemispaceNurseryEnabled);
+      break;
+    }
     case JSGC_MIN_EMPTY_CHUNK_COUNT:
       setMinEmptyChunkCount(TuningDefaults::MinEmptyChunkCount, lock);
       break;
@@ -1241,6 +1251,8 @@ uint32_t GCRuntime::getParameter(JSGCParamKey key, const AutoLockGC& lock) {
       return parallelMarkingEnabled;
     case JSGC_INCREMENTAL_WEAKMAP_ENABLED:
       return marker().incrementalWeakMapMarkingEnabled;
+    case JSGC_SEMISPACE_NURSERY_ENABLED:
+      return nursery().semispaceEnabled();
     case JSGC_CHUNK_BYTES:
       return ChunkSize;
     case JSGC_HELPER_THREAD_RATIO:

js/src/gc/GC.h

@@ -83,7 +83,8 @@ class TenuredChunk;
   _("maxHelperThreads", JSGC_MAX_HELPER_THREADS, true)                      \
   _("helperThreadCount", JSGC_HELPER_THREAD_COUNT, false)                   \
   _("markingThreadCount", JSGC_MARKING_THREAD_COUNT, true)                  \
-  _("systemPageSizeKB", JSGC_SYSTEM_PAGE_SIZE_KB, false)
+  _("systemPageSizeKB", JSGC_SYSTEM_PAGE_SIZE_KB, false)                    \
+  _("semispaceNurseryEnabled", JSGC_SEMISPACE_NURSERY_ENABLED, true)
 
 // Get the key and writability give a GC parameter name.
 extern bool GetGCParameterInfo(const char* name, JSGCParamKey* keyOut,

js/src/gc/Nursery.cpp

@@ -223,6 +223,7 @@ js::Nursery::Nursery(GCRuntime* gc)
       startPosition_(0),
       capacity_(0),
       enableProfiling_(false),
+      semispaceEnabled_(gc::TuningDefaults::SemispaceNurseryEnabled),
       canAllocateStrings_(true),
       canAllocateBigInts_(true),
       reportDeduplications_(false),
@@ -464,6 +465,20 @@ void js::Nursery::discardCodeAndSetJitFlagsForZone(JS::Zone* zone) {
   }
 }
 
+void js::Nursery::setSemispaceEnabled(bool enabled) {
+  if (semispaceEnabled() == enabled) {
+    return;
+  }
+
+  if (!isEmpty()) {
+    gc->minorGC(JS::GCReason::EVICT_NURSERY);
+  }
+
+  disable();
+  semispaceEnabled_ = enabled;
+  enable();
+}
+
 bool js::Nursery::isEmpty() const {
   if (!isEnabled()) {
     return true;

js/src/gc/Nursery.h

@@ -103,6 +103,9 @@ class Nursery {
   void disableBigInts();
   bool canAllocateBigInts() const { return canAllocateBigInts_; }
 
+  void setSemispaceEnabled(bool enabled);
+  bool semispaceEnabled() const { return semispaceEnabled_; }
+
   // Return true if no allocations have been made since the last collection.
   bool isEmpty() const;
 
@@ -553,6 +556,9 @@ class Nursery {
 
   mozilla::TimeDuration profileThreshold_;
 
+  // Whether to use semispace collection.
+  bool semispaceEnabled_;
+
   // Whether we will nursery-allocate strings.
   bool canAllocateStrings_;
 

js/src/gc/Scheduling.h

@@ -536,6 +536,9 @@ static const bool ParallelMarkingEnabled = false;
 /* JSGC_INCREMENTAL_WEAKMAP_ENABLED */
 static const bool IncrementalWeakMapMarkingEnabled = true;
 
+/* JSGC_SEMISPACE_NURSERY_ENABLED */
+static const bool SemispaceNurseryEnabled = false;
+
 /* JSGC_HELPER_THREAD_RATIO */
 static const double HelperThreadRatio = 0.5;
 

js/src/jit-test/tests/gc/gcparam.js

@@ -60,3 +60,4 @@ testChangeParam("mallocThresholdBase");
 testChangeParam("urgentThreshold");
 testChangeParam("helperThreadRatio");
 testChangeParam("maxHelperThreads");
+testChangeParam("semispaceNurseryEnabled");

modules/libpref/init/all.js

@@ -959,6 +959,11 @@ pref("javascript.options.mem.gc_incremental_slice_ms", 5);
 // JSGC_COMPACTING_ENABLED
 pref("javascript.options.mem.gc_compacting", true);
 
+#ifdef NIGHTLY_BUILD
+// JSGC_SEMISPACE_NURSERY_ENABLED
+pref("javascript.options.mem.gc_experimental_semispace_nursery", false);
+#endif
+
 // JSGC_PARALLEL_MARKING_ENABLED
 // This only applies to the main runtime and does not affect workers.
 #ifndef ANDROID