[test] Enable random marking start points.

Stress marking by starting it in random points between 0 and
--stress_marking percent of the standard limit.

Bug: v8:6972

Change-Id: I84572ba937f34cf4fd7b5eb2d532f48ff122a060
Reviewed-on: https://chromium-review.googlesource.com/763453
Commit-Queue: Michał Majewski <majeski@google.com>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49332}

src/flag-definitions.h

@@ -679,8 +679,9 @@ DEFINE_INT(stress_compaction_percentage, 0,
            "candidates. It overrides stress_compaction.")
 DEFINE_BOOL(stress_incremental_marking, false,
             "force incremental marking for small heaps and run it more often")
-DEFINE_INT(stress_incremental_marking_percentage, 0,
-           "force incremental marking after X percent of the standard limit")
+DEFINE_INT(stress_marking, 0,
+           "force marking at random points between 0 and X (inclusive) percent "
+           "of the regular marking start limit")
 DEFINE_BOOL(manual_evacuation_candidates_selection, false,
             "Test mode only flag. It allows an unit test to select evacuation "
             "candidates pages (requires --stress_compaction).")

src/heap/heap.cc

@@ -5346,7 +5346,7 @@ Heap::IncrementalMarkingLimit Heap::IncrementalMarkingLimitReached() {
     return IncrementalMarkingLimit::kHardLimit;
   }
 
-  if (FLAG_stress_incremental_marking_percentage > 0) {
+  if (FLAG_stress_marking > 0) {
     double gained_since_last_gc =
         PromotedSinceLastGC() +
         (external_memory_ - external_memory_at_last_mark_compact_);
@@ -5361,8 +5361,8 @@ Heap::IncrementalMarkingLimit Heap::IncrementalMarkingLimitReached() {
             current_percent);
       }
 
-      if (static_cast<int>(current_percent) >=
-          FLAG_stress_incremental_marking_percentage) {
+      if (static_cast<int>(current_percent) >= stress_marking_percentage_) {
+        stress_marking_percentage_ = NextStressMarkingLimit();
         return IncrementalMarkingLimit::kHardLimit;
       }
     }
@@ -5514,6 +5514,10 @@ bool Heap::SetUp() {
   SetGetExternallyAllocatedMemoryInBytesCallback(
       DefaultGetExternallyAllocatedMemoryInBytesCallback);
 
+  if (FLAG_stress_marking > 0) {
+    stress_marking_percentage_ = NextStressMarkingLimit();
+  }
+
   return true;
 }
 
@@ -5550,6 +5554,9 @@ void Heap::PrintAllocationsHash() {
   PrintF("\n### Allocations = %u, hash = 0x%08x\n", allocations_count(), hash);
 }
 
+int Heap::NextStressMarkingLimit() {
+  return isolate()->fuzzer_rng()->NextInt(FLAG_stress_marking + 1);
+}
 
 void Heap::NotifyDeserializationComplete() {
   PagedSpaces spaces(this);

src/heap/heap.h

@@ -1802,6 +1802,8 @@ class Heap {
   inline void UpdateAllocationsHash(uint32_t value);
   void PrintAllocationsHash();
 
+  int NextStressMarkingLimit();
+
   void AddToRingBuffer(const char* string);
   void GetFromRingBuffer(char* buffer);
 
@@ -2293,6 +2295,10 @@ class Heap {
   // Running hash over allocations performed.
   uint32_t raw_allocations_hash_;
 
+  // Starts marking when stress_marking_percentage_% of the marking start limit
+  // is reached.
+  int stress_marking_percentage_;
+
   // How many mark-sweep collections happened.
   unsigned int ms_count_;