Fix OOM bug 3976.

src/heap/mark-compact.cc

 // Copyright 2012 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/v8.h"
 
 #include "src/base/atomicops.h"
 #include "src/base/bits.h"
 #include "src/code-stubs.h"
 #include "src/compilation-cache.h"
@@ skipping 581 matching lines @@
   return NULL;
 }
 
 
 // Returns zero for pages that have so little fragmentation that it is not
 // worth defragmenting them.  Otherwise a positive integer that gives an
 // estimate of fragmentation on an arbitrary scale.
 static int FreeListFragmentation(PagedSpace* space, Page* p) {
   // If page was not swept then there are no free list items on it.
   if (!p->WasSwept()) {
-    if (FLAG_trace_fragmentation) {
+    if (FLAG_trace_fragmentation_verbose) {
       PrintF("%p [%s]: %d bytes live (unswept)\n", reinterpret_cast<void*>(p),
              AllocationSpaceName(space->identity()), p->LiveBytes());
     }
-    return 0;
+    return FLAG_always_compact ? 1 : 0;
   }
 
   PagedSpace::SizeStats sizes;
   space->ObtainFreeListStatistics(p, &sizes);
 
   intptr_t ratio;
   intptr_t ratio_threshold;
   intptr_t area_size = space->AreaSize();
   if (space->identity() == CODE_SPACE) {
     ratio = (sizes.medium_size_ * 10 + sizes.large_size_ * 2) * 100 / area_size;
     ratio_threshold = 10;
   } else {
     ratio = (sizes.small_size_ * 5 + sizes.medium_size_) * 100 / area_size;
     ratio_threshold = 15;
   }
 
-  if (FLAG_trace_fragmentation) {
+  if (FLAG_trace_fragmentation_verbose) {
     PrintF("%p [%s]: %d (%.2f%%) %d (%.2f%%) %d (%.2f%%) %d (%.2f%%) %s\n",
            reinterpret_cast<void*>(p), AllocationSpaceName(space->identity()),
            static_cast<int>(sizes.small_size_),
            static_cast<double>(sizes.small_size_ * 100) / area_size,
            static_cast<int>(sizes.medium_size_),
            static_cast<double>(sizes.medium_size_ * 100) / area_size,
            static_cast<int>(sizes.large_size_),
            static_cast<double>(sizes.large_size_ * 100) / area_size,
            static_cast<int>(sizes.huge_size_),
            static_cast<double>(sizes.huge_size_ * 100) / area_size,
@@ skipping 55 matching lines @@
 
 
   if (over_reserved > reserved / 3 && over_reserved >= 2 * space->AreaSize()) {
     // If over-usage is very high (more than a third of the space), we
     // try to free all mostly empty pages.  We expect that almost empty
     // pages are even easier to compact so bump the limit even more.
     mode = REDUCE_MEMORY_FOOTPRINT;
     max_evacuation_candidates *= 2;
   }
 
+  if (FLAG_always_compact) {
+    max_evacuation_candidates = kMaxMaxEvacuationCandidates;
+  }
+
   if (FLAG_trace_fragmentation && mode == REDUCE_MEMORY_FOOTPRINT) {
     PrintF(
         "Estimated over reserved memory: %.1f / %.1f MB (threshold %d), "
         "evacuation candidate limit: %d\n",
         static_cast<double>(over_reserved) / MB,
         static_cast<double>(reserved) / MB,
         static_cast<int>(kFreenessThreshold), max_evacuation_candidates);
   }
 
   intptr_t estimated_release = 0;
 
   Candidate candidates[kMaxMaxEvacuationCandidates];
 
+  if (FLAG_trace_fragmentation &&
+      max_evacuation_candidates >= kMaxMaxEvacuationCandidates) {
+    PrintF("Hit max page compaction limit of %d pages\n",
+           kMaxMaxEvacuationCandidates);
+  }
   max_evacuation_candidates =
       Min(kMaxMaxEvacuationCandidates, max_evacuation_candidates);
 
   int count = 0;
   int fragmentation = 0;
   Candidate* least = NULL;
 
   PageIterator it(space);
   while (it.has_next()) {
     Page* p = it.next();
     if (p->NeverEvacuate()) continue;
 
     // Invariant: Evacuation candidates are just created when marking is
     // started. At the end of a GC all evacuation candidates are cleared and
     // their slot buffers are released.
     CHECK(!p->IsEvacuationCandidate());
     CHECK(p->slots_buffer() == NULL);
 
     if (FLAG_stress_compaction) {
       unsigned int counter = space->heap()->ms_count();
       uintptr_t page_number = reinterpret_cast<uintptr_t>(p) >> kPageSizeBits;
       if ((counter & 1) == (page_number & 1)) fragmentation = 1;
-    } else if (mode == REDUCE_MEMORY_FOOTPRINT) {
+    } else if (mode == REDUCE_MEMORY_FOOTPRINT && !FLAG_always_compact) {
       // Don't try to release too many pages.
       if (estimated_release >= over_reserved) {
         continue;
       }
 
       intptr_t free_bytes = 0;
 
       if (!p->WasSwept()) {
         free_bytes = (p->area_size() - p->LiveBytes());
       } else {
         PagedSpace::SizeStats sizes;
         space->ObtainFreeListStatistics(p, &sizes);
         free_bytes = sizes.Total();
       }
 
       int free_pct = static_cast<int>(free_bytes * 100) / p->area_size();
 
       if (free_pct >= kFreenessThreshold) {
         estimated_release += free_bytes;
         fragmentation = free_pct;
       } else {
         fragmentation = 0;
       }
 
-      if (FLAG_trace_fragmentation) {
+      if (FLAG_trace_fragmentation_verbose) {
         PrintF("%p [%s]: %d (%.2f%%) free %s\n", reinterpret_cast<void*>(p),
                AllocationSpaceName(space->identity()),
                static_cast<int>(free_bytes),
                static_cast<double>(free_bytes * 100) / p->area_size(),
                (fragmentation > 0) ? "[fragmented]" : "");
       }
     } else {
       fragmentation = FreeListFragmentation(space, p);
     }
 
@@ skipping 2465 matching lines @@
 
     // Clear marking bits for current cell.
     *cell = 0;
   }
   p->ResetLiveBytes();
 }
 
 
 void MarkCompactCollector::EvacuatePages() {
   int npages = evacuation_candidates_.length();
+  int abandoned_pages = 0;
   for (int i = 0; i < npages; i++) {
     Page* p = evacuation_candidates_[i];
     DCHECK(p->IsEvacuationCandidate() ||
            p->IsFlagSet(Page::RESCAN_ON_EVACUATION));
     DCHECK(static_cast<int>(p->parallel_sweeping()) ==
            MemoryChunk::SWEEPING_DONE);
     PagedSpace* space = static_cast<PagedSpace*>(p->owner());
     // Allocate emergency memory for the case when compaction fails due to out
     // of memory.
     if (!space->HasEmergencyMemory()) {
       space->CreateEmergencyMemory();
     }
     if (p->IsEvacuationCandidate()) {
       // During compaction we might have to request a new page. Check that we
       // have an emergency page and the space still has room for that.
-      if (space->HasEmergencyMemory() && space->CanExpand()) {
+      if (space->HasEmergencyMemory() || space->CanExpand()) {
         EvacuateLiveObjectsFromPage(p);
         // Unlink the page from the list of pages here. We must not iterate
         // over that page later (e.g. when scan on scavenge pages are
         // processed). The page itself will be freed later and is still
         // reachable from the evacuation candidates list.
         p->Unlink();
       } else {
         // Without room for expansion evacuation is not guaranteed to succeed.
         // Pessimistically abandon unevacuated pages.
         for (int j = i; j < npages; j++) {
           Page* page = evacuation_candidates_[j];
           slots_buffer_allocator_.DeallocateChain(page->slots_buffer_address());
           page->ClearEvacuationCandidate();
           page->SetFlag(Page::RESCAN_ON_EVACUATION);
         }
+        abandoned_pages = npages - i;
         break;
       }
     }
   }
   if (npages > 0) {
     // Release emergency memory.
     PagedSpaces spaces(heap());
     for (PagedSpace* space = spaces.next(); space != NULL;
          space = spaces.next()) {
       if (space->HasEmergencyMemory()) {
         space->FreeEmergencyMemory();
       }
     }
+    if (FLAG_trace_fragmentation) {
+      if (abandoned_pages != 0) {
+        PrintF(
+            "  Abandon %d out of %d page defragmentations due to lack of "
+            "memory\n",
+            abandoned_pages, npages);
+      } else {
+        PrintF("  Defragmented %d pages\n", npages);
+      }
+    }
   }
 }
 
 
 class EvacuationWeakObjectRetainer : public WeakObjectRetainer {
  public:
   virtual Object* RetainAs(Object* object) {
     if (object->IsHeapObject()) {
       HeapObject* heap_object = HeapObject::cast(object);
       MapWord map_word = heap_object->map_word();
@@ skipping 323 matching lines @@
     StoreBufferRebuildScope scope(heap_, heap_->store_buffer(),
                                   &Heap::ScavengeStoreBufferCallback);
     heap_->store_buffer()->IteratePointersToNewSpace(&UpdatePointer);
   }
 
   {
     GCTracer::Scope gc_scope(heap()->tracer(),
                              GCTracer::Scope::MC_UPDATE_POINTERS_TO_EVACUATED);
     SlotsBuffer::UpdateSlotsRecordedIn(heap_, migration_slots_buffer_,
                                        code_slots_filtering_required);
-    if (FLAG_trace_fragmentation) {
+    if (FLAG_trace_fragmentation_verbose) {
       PrintF("  migration slots buffer: %d\n",
              SlotsBuffer::SizeOfChain(migration_slots_buffer_));
     }
 
     if (compacting_ && was_marked_incrementally_) {
       // It's difficult to filter out slots recorded for large objects.
       LargeObjectIterator it(heap_->lo_space());
       for (HeapObject* obj = it.Next(); obj != NULL; obj = it.Next()) {
         // LargeObjectSpace is not swept yet thus we have to skip
         // dead objects explicitly.
@@ skipping 14 matching lines @@
         heap()->tracer(),
         GCTracer::Scope::MC_UPDATE_POINTERS_BETWEEN_EVACUATED);
     for (int i = 0; i < npages; i++) {
       Page* p = evacuation_candidates_[i];
       DCHECK(p->IsEvacuationCandidate() ||
              p->IsFlagSet(Page::RESCAN_ON_EVACUATION));
 
       if (p->IsEvacuationCandidate()) {
         SlotsBuffer::UpdateSlotsRecordedIn(heap_, p->slots_buffer(),
                                            code_slots_filtering_required);
-        if (FLAG_trace_fragmentation) {
+        if (FLAG_trace_fragmentation_verbose) {
           PrintF("  page %p slots buffer: %d\n", reinterpret_cast<void*>(p),
                  SlotsBuffer::SizeOfChain(p->slots_buffer()));
         }
 
         // Important: skip list should be cleared only after roots were updated
         // because root iteration traverses the stack and might have to find
         // code objects from non-updated pc pointing into evacuation candidate.
         SkipList* list = p->skip_list();
         if (list != NULL) list->Clear();
       } else {
@@ skipping 918 matching lines @@
   SlotsBuffer* buffer = *buffer_address;
   while (buffer != NULL) {
     SlotsBuffer* next_buffer = buffer->next();
     DeallocateBuffer(buffer);
     buffer = next_buffer;
   }
   *buffer_address = NULL;
 }
 }
 }  // namespace v8::internal