Force scavenge in idle notification if we estimate that it will take long.

src/heap/gc-idle-time-handler.cc

 // Copyright 2014 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/gc-idle-time-handler.h"
 #include "src/heap/gc-tracer.h"
 #include "src/utils.h"
 
 namespace v8 {
 namespace internal {
@@ skipping 53 matching lines @@
 size_t GCIdleTimeHandler::EstimateMarkCompactTime(
     size_t size_of_objects, size_t mark_compact_speed_in_bytes_per_ms) {
   if (mark_compact_speed_in_bytes_per_ms == 0) {
     mark_compact_speed_in_bytes_per_ms = kInitialConservativeMarkCompactSpeed;
   }
   size_t result = size_of_objects / mark_compact_speed_in_bytes_per_ms;
   return Min(result, kMaxMarkCompactTimeInMs);
 }
 
 
-size_t GCIdleTimeHandler::EstimateScavengeTime(
-    size_t new_space_size, size_t scavenge_speed_in_bytes_per_ms) {
+bool GCIdleTimeHandler::DoScavenge(
+    size_t idle_time_in_ms, size_t new_space_size, size_t used_new_space_size,
+    size_t scavenge_speed_in_bytes_per_ms,
+    size_t new_space_allocation_throughput_in_bytes_per_ms) {
+  size_t new_space_allocation_limit =
+      kMaxFrameRenderingIdleTime * scavenge_speed_in_bytes_per_ms;
+
+  // If the limit is larger than the new space size, then scavenging used to be
+  // really fast. We can take advantage of the whole new space.
+  if (new_space_allocation_limit > new_space_size) {
+    new_space_allocation_limit = new_space_size;
+  }
+
+  // We have to trigger scavenge before we reach the end of new space.
+  new_space_allocation_limit -=
+      new_space_allocation_throughput_in_bytes_per_ms *
+      kMaxFrameRenderingIdleTime;
+
   if (scavenge_speed_in_bytes_per_ms == 0) {
     scavenge_speed_in_bytes_per_ms = kInitialConservativeScavengeSpeed;
   }
-  return new_space_size / scavenge_speed_in_bytes_per_ms;
-}
 
-
-bool GCIdleTimeHandler::ScavangeMayHappenSoon(
-    size_t available_new_space_memory,
-    size_t new_space_allocation_throughput_in_bytes_per_ms) {
-  if (available_new_space_memory <=
-      new_space_allocation_throughput_in_bytes_per_ms *
-          kMaxFrameRenderingIdleTime) {
-    return true;
+  if (new_space_allocation_limit <= used_new_space_size) {
+    if (used_new_space_size / scavenge_speed_in_bytes_per_ms <=
+        idle_time_in_ms) {
+      return true;
+    }
   }
   return false;
 }
 
 
 // The following logic is implemented by the controller:
-// (1) If the new space is almost full and we can effort a Scavenge, then a
-// Scavenge is performed.
+// (1) If the new space is almost full and we can effort a Scavenge or if the

[ulan, 2014/09/26 08:12:22]

nit: "we can _afford_ a Scavenge"?

[Hannes Payer (out of office), 2014/10/02 07:22:09]

Done.

+// next Scavenge will very likely take long, then a Scavenge is performed.
 // (2) If there is currently no MarkCompact idle round going on, we start a
 // new idle round if enough garbage was created or we received a context
 // disposal event. Otherwise we do not perform garbage collection to keep
 // system utilization low.
 // (3) If incremental marking is done, we perform a full garbage collection
 // if context was disposed or if we are allowed to still do full garbage
 // collections during this idle round or if we are not allowed to start
 // incremental marking. Otherwise we do not perform garbage collection to
 // keep system utilization low.
 // (4) If sweeping is in progress and we received a large enough idle time
 // request, we finalize sweeping here.
 // (5) If incremental marking is in progress, we perform a marking step. Note,
 // that this currently may trigger a full garbage collection.
 GCIdleTimeAction GCIdleTimeHandler::Compute(size_t idle_time_in_ms,
                                             HeapState heap_state) {
-  if (ScavangeMayHappenSoon(
-          heap_state.available_new_space_memory,
-          heap_state.new_space_allocation_throughput_in_bytes_per_ms) &&
-      idle_time_in_ms >=
-          EstimateScavengeTime(heap_state.new_space_capacity,
-                               heap_state.scavenge_speed_in_bytes_per_ms)) {
+  if (DoScavenge(idle_time_in_ms, heap_state.new_space_capacity,
+                 heap_state.used_new_space_size,
+                 heap_state.scavenge_speed_in_bytes_per_ms,
+                 heap_state.new_space_allocation_throughput_in_bytes_per_ms)) {
     return GCIdleTimeAction::Scavenge();
   }
+
   if (IsMarkCompactIdleRoundFinished()) {
     if (EnoughGarbageSinceLastIdleRound() || heap_state.contexts_disposed > 0) {
       StartIdleRound();
     } else {
       return GCIdleTimeAction::Done();
     }
   }
 
   if (idle_time_in_ms == 0) {
     return GCIdleTimeAction::Nothing();
@@ skipping 33 matching lines @@
   if (heap_state.incremental_marking_stopped &&
       !heap_state.can_start_incremental_marking) {
     return GCIdleTimeAction::Nothing();
   }
   size_t step_size = EstimateMarkingStepSize(
       idle_time_in_ms, heap_state.incremental_marking_speed_in_bytes_per_ms);
   return GCIdleTimeAction::IncrementalMarking(step_size);
 }
 }
 }