doubly-linked free-lists for thread caches and page heaps

third_party/tcmalloc/chromium/src/common.h

Index: third_party/tcmalloc/chromium/src/common.h
diff --git a/third_party/tcmalloc/chromium/src/common.h b/third_party/tcmalloc/chromium/src/common.h
index a3df8de02fd0056b750e096d0d74eb5477cde6bb..78cdc036ceb27bf3538d6c3411810f9a27757ce9 100644
--- a/third_party/tcmalloc/chromium/src/common.h
+++ b/third_party/tcmalloc/chromium/src/common.h
@@ -31,7 +31,6 @@
 // Author: Sanjay Ghemawat <opensource@google.com>
 //
 // Common definitions for tcmalloc code.
-
 #ifndef TCMALLOC_COMMON_H_
 #define TCMALLOC_COMMON_H_
 
@@ -40,6 +39,7 @@
 #ifdef HAVE_STDINT_H
 #include <stdint.h>                     // for uintptr_t, uint64_t
 #endif
+#include "free_list.h"  // for SIZE_CLASS macros
 #include "internal_logging.h"  // for ASSERT, etc
 
 // Type that can hold a page number
@@ -61,19 +61,30 @@ typedef uintptr_t Length;
 // central lists.  Also, larger pages are less likely to get freed.
 // These two factors cause a bounded increase in memory use.
 
+static const size_t kAlignment  = 8;
+
+// Constants dependant on tcmalloc configuration and archetecture.
+// We need to guarantee the smallest class size is big enough to hold the
+// pointers that form the free list.
+static const size_t kNumFreeListPointers = 
+  (tcmalloc::kSupportsDoublyLinkedList ? 2 : 1);
+static const size_t kLinkSize = kNumFreeListPointers * sizeof(void *);
+static const size_t kMinClassSize = 
+  (kLinkSize > kAlignment ? kLinkSize : kAlignment);
+static const size_t kSkippedClasses = (kAlignment < kMinClassSize ? 1 : 0);
+
 #if defined(TCMALLOC_LARGE_PAGES)
 static const size_t kPageShift  = 15;
-static const size_t kNumClasses = 95;
+static const size_t kNumClasses = 95 - kSkippedClasses;
 static const size_t kMaxThreadCacheSize = 4 << 20;
 #else
 static const size_t kPageShift  = 12;
-static const size_t kNumClasses = 61;
+static const size_t kNumClasses = 61 - kSkippedClasses;
 static const size_t kMaxThreadCacheSize = 2 << 20;
 #endif
 
 static const size_t kPageSize   = 1 << kPageShift;
 static const size_t kMaxSize    = 8u * kPageSize;
-static const size_t kAlignment  = 8;
 // For all span-lengths < kMaxPages we keep an exact-size list.
 static const size_t kMaxPages = 1 << (20 - kPageShift);