Use an allocation site scratchpad to speed up allocaton site processing during gc.

src/heap.cc

Index: src/heap.cc
diff --git a/src/heap.cc b/src/heap.cc
index b9e1a2b323a36664d1e53e84e7c7e899f2f9817e..3ff9a49aa79a867995112155f30aee7ba8bb9c04 100644
--- a/src/heap.cc
+++ b/src/heap.cc
@@ -148,6 +148,7 @@ Heap::Heap()
 #ifdef VERIFY_HEAP
       no_weak_object_verification_scope_depth_(0),
 #endif
+      allocation_sites_scratchpad_pointer(0),

[mvstanton, 2013/12/13 10:30:17]

How about using the word count or length instead of pointer for the name.

[Hannes Payer (out of office), 2013/12/18 14:29:19]

Done.

       promotion_queue_(this),
       configured_(false),
       chunks_queued_for_free_(NULL),
@@ -504,25 +505,52 @@ void Heap::RepairFreeListsAfterBoot() {
 }
 
 
-void Heap::GarbageCollectionEpilogue() {
+void Heap::ProcessPretenuringFeedback() {
   if (FLAG_allocation_site_pretenuring) {
     int tenure_decisions = 0;
     int dont_tenure_decisions = 0;
     int allocation_mementos_found = 0;
-
-    Object* cur = allocation_sites_list();
-    while (cur->IsAllocationSite()) {
-      AllocationSite* casted = AllocationSite::cast(cur);
-      allocation_mementos_found += casted->memento_found_count()->value();
-      if (casted->DigestPretenuringFeedback()) {
-        if (casted->GetPretenureMode() == TENURED) {
-          tenure_decisions++;
-        } else {
-          dont_tenure_decisions++;
+    int allocation_sites = 0;
+    int active_allocation_sites = 0;
+    bool use_scratchpad =
+        allocation_sites_scratchpad_pointer < kAllocationSiteScratchpadSize;
+
+    if (use_scratchpad) {

[Hannes Payer (out of office), 2013/12/12 15:26:05]

Should I make an Iterator for that duplicated piece of code?

[mvstanton, 2013/12/13 10:30:17]

Yep that is a good idea. Alternatively, a function that accepts an
AllocationSite, but I see it would have to accept all these statistics variables
which wouldn't be fun.

[Hannes Payer (out of office), 2013/12/18 14:29:19]

I decided to do the simplified version, not beautiful but an extra iterator is
overkill. WDYT?

+      for (int i = 0; i < allocation_sites_scratchpad_pointer; i++) {
+        AllocationSite* casted = allocation_sites_scratchpad[i];
+        allocation_mementos_found += casted->memento_found_count()->value();
+        if (casted->memento_found_count()->value() > 0) {
+          active_allocation_sites++;
+        }
+        if (casted->DigestPretenuringFeedback()) {
+          if (casted->GetPretenureMode() == TENURED) {
+            tenure_decisions++;
+          } else {
+            dont_tenure_decisions++;
+          }
+        }
+        allocation_sites++;
+      }
+    } else {
+      Object* cur = allocation_sites_list();
+      while (cur->IsAllocationSite()) {
+        AllocationSite* casted = AllocationSite::cast(cur);
+        allocation_mementos_found += casted->memento_found_count()->value();
+        if (casted->memento_found_count()->value() > 0) {
+          active_allocation_sites++;
+        }
+        if (casted->DigestPretenuringFeedback()) {
+          if (casted->GetPretenureMode() == TENURED) {
+            tenure_decisions++;
+          } else {
+            dont_tenure_decisions++;
+          }
         }
+        cur = casted->weak_next();
+        allocation_sites++;
       }
-      cur = casted->weak_next();
     }
+    allocation_sites_scratchpad_pointer = 0;
 
     // TODO(mvstanton): Pretenure decisions are only made once for an allocation
     // site. Find a sane way to decide about revisiting the decision later.
@@ -531,14 +559,21 @@ void Heap::GarbageCollectionEpilogue() {
         (allocation_mementos_found > 0 ||
          tenure_decisions > 0 ||
          dont_tenure_decisions > 0)) {
-      PrintF("GC: (#mementos, #tenure decisions, #donttenure decisions) "
-             "(%d, %d, %d)\n",
+      PrintF("GC(%d): (#allocation sites, #active allocation sites, "
+             "#mementos, #tenure decisions, #donttenure decisions) "
+             "(%d, %d, %d, %d, %d)\n",
+             use_scratchpad,
+             allocation_sites,
+             active_allocation_sites,
              allocation_mementos_found,
              tenure_decisions,
              dont_tenure_decisions);
     }
   }
+}
+
 
+void Heap::GarbageCollectionEpilogue() {
   store_buffer()->GCEpilogue();
 
   // In release mode, we only zap the from space under heap verification.
@@ -1565,6 +1600,8 @@ void Heap::Scavenge() {
   IncrementYoungSurvivorsCounter(static_cast<int>(
       (PromotedSpaceSizeOfObjects() - survived_watermark) + new_space_.Size()));
 
+  ProcessPretenuringFeedback();
+
   LOG(isolate_, ResourceEvent("scavenge", "end"));
 
   gc_state_ = NOT_IN_GC;