Ensure the memory reduces makes progress.

src/heap/memory-reducer.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/heap/memory-reducer.h"
 
 #include "src/flags.h"
 #include "src/heap/heap.h"
 #include "src/utils.h"
 #include "src/v8.h"
 
 namespace v8 {
 namespace internal {
 
 const int MemoryReducer::kLongDelayMs = 5000;
 const int MemoryReducer::kShortDelayMs = 500;
+const int MemoryReducer::kWatchdogDelayMs = 100000;
 const int MemoryReducer::kMaxNumberOfGCs = 3;
 
 MemoryReducer::TimerTask::TimerTask(MemoryReducer* memory_reducer)
     : CancelableTask(memory_reducer->heap()->isolate()),
       memory_reducer_(memory_reducer) {}
 
 
 void MemoryReducer::TimerTask::RunInternal() {
   Heap* heap = memory_reducer_->heap();
   Event event;
@@ skipping 76 matching lines @@
                    state_.started_gcs);
     }
   }
 }
 
 
 // For specification of this function see the comment for MemoryReducer class.
 MemoryReducer::State MemoryReducer::Step(const State& state,
                                          const Event& event) {
   if (!FLAG_incremental_marking) {
-    return State(kDone, 0, 0);
+    return State(kDone, 0, 0, state.last_gc_time_ms);
   }
   switch (state.action) {
     case kDone:
       if (event.type == kTimer || event.type == kBackgroundIdleNotification) {
         return state;
       } else {
         DCHECK(event.type == kContextDisposed || event.type == kMarkCompact);
-        return State(kWait, 0, event.time_ms + kLongDelayMs);
+        return State(
+            kWait, 0, event.time_ms + kLongDelayMs,
+            event.type == kMarkCompact ? event.time_ms : state.last_gc_time_ms);
       }
     case kWait:
       switch (event.type) {
         case kContextDisposed:
           return state;
         case kTimer:
           if (state.started_gcs >= kMaxNumberOfGCs) {
-            return State(kDone, 0, 0.0);
+            return State(kDone, 0, 0.0, state.last_gc_time_ms);
           } else if (event.can_start_incremental_gc &&
-                     event.low_allocation_rate) {
+                     (event.low_allocation_rate ||
+                      (state.last_gc_time_ms != 0 &&

[ulan, 2015/07/30 13:20:19]

This is the main change.

Other lines in this function ensure that state.last_gc_time_ms = event.time_ms
for mark-compact event or doesn't change.

[Hannes Payer (out of office), 2015/07/30 14:28:03]

Can we make the watchdog part a boolean function to increase readability?

[ulan, 2015/07/31 09:47:43]

Done.

+                       event.time_ms >
+                           state.last_gc_time_ms + kWatchdogDelayMs))) {
             if (state.next_gc_start_ms <= event.time_ms) {
-              return State(kRun, state.started_gcs + 1, 0.0);
+              return State(kRun, state.started_gcs + 1, 0.0,
+                           state.last_gc_time_ms);
             } else {
               return state;
             }
           } else {
-            return State(kWait, state.started_gcs,
-                         event.time_ms + kLongDelayMs);
+            return State(kWait, state.started_gcs, event.time_ms + kLongDelayMs,
+                         state.last_gc_time_ms);
           }
         case kBackgroundIdleNotification:
           if (event.can_start_incremental_gc &&
               state.started_gcs < kMaxNumberOfGCs) {
             return State(kWait, state.started_gcs + 1,
-                         event.time_ms + kLongDelayMs);
+                         event.time_ms + kLongDelayMs, state.last_gc_time_ms);
           } else {
             return state;
           }
         case kMarkCompact:
-          return State(kWait, state.started_gcs, event.time_ms + kLongDelayMs);
+          return State(kWait, state.started_gcs, event.time_ms + kLongDelayMs,
+                       event.time_ms);
       }
     case kRun:
       if (event.type != kMarkCompact) {
         return state;
       } else {
         if (state.started_gcs < kMaxNumberOfGCs &&
             (event.next_gc_likely_to_collect_more || state.started_gcs == 1)) {
-          return State(kWait, state.started_gcs, event.time_ms + kShortDelayMs);
+          return State(kWait, state.started_gcs, event.time_ms + kShortDelayMs,
+                       event.time_ms);
         } else {
-          return State(kDone, 0, 0.0);
+          return State(kDone, 0, 0.0, event.time_ms);
         }
       }
   }
   UNREACHABLE();
-  return State(kDone, 0, 0);  // Make the compiler happy.
+  return State(kDone, 0, 0, 0.0);  // Make the compiler happy.
 }
 
 
 void MemoryReducer::ScheduleTimer(double delay_ms) {
   DCHECK(delay_ms > 0);
   // Leave some room for precision error in task scheduler.
   const double kSlackMs = 100;
   v8::Isolate* isolate = reinterpret_cast<v8::Isolate*>(heap()->isolate());
   auto timer_task = new MemoryReducer::TimerTask(this);
   V8::GetCurrentPlatform()->CallDelayedOnForegroundThread(
       isolate, timer_task, (delay_ms + kSlackMs) / 1000.0);
 }
 
 
-void MemoryReducer::TearDown() {
-  state_ = State(kDone, 0, 0);
-}
+void MemoryReducer::TearDown() { state_ = State(kDone, 0, 0, 0.0); }
 
 }  // internal
 }  // v8