More robust when allocation fails during compaction

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 3336 matching lines @@
   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();
+      space->CreateEmergencyMemory();  // If the OS lets us.
     }
     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()) {
+      // During compaction we might have to request a new page in order to free
+      // up a page.  Check that we actually got an emergency page above so we
+      // can guarantee that this succeeds.
+      if (space->HasEmergencyMemory()) {
         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++) {
@@ skipping 1424 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