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

third_party/tcmalloc/chromium/src/common.h

 // Copyright (c) 2008, Google Inc.
 // All rights reserved.
 // 
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 // 
 //     * Redistributions of source code must retain the above copyright
 // notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
@@ skipping 13 matching lines @@
 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 // ---
 // Author: Sanjay Ghemawat <opensource@google.com>
 //
 // Common definitions for tcmalloc code.
-
 #ifndef TCMALLOC_COMMON_H_
 #define TCMALLOC_COMMON_H_
 
 #include "config.h"
 #include <stddef.h>                     // for size_t
 #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
 typedef uintptr_t PageID;
 
 // Type that can hold the length of a run of pages
 typedef uintptr_t Length;
 
 //-------------------------------------------------------------------
 // Configuration
 //-------------------------------------------------------------------
 
 // Using large pages speeds up the execution at a cost of larger memory use.
 // Deallocation may speed up by a factor as the page map gets 8x smaller, so
 // lookups in the page map result in fewer L2 cache misses, which translates to
 // speedup for application/platform combinations with high L2 cache pressure.
 // As the number of size classes increases with large pages, we increase
 // the thread cache allowance to avoid passing more free ranges to and from
 // 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);
 
 // Default bound on the total amount of thread caches.
 #ifdef TCMALLOC_SMALL_BUT_SLOW
 // Make the overall thread cache no bigger than that of a single thread
 // for the small memory footprint case.
 static const size_t kDefaultOverallThreadCacheSize = kMaxThreadCacheSize;
 #else
 static const size_t kDefaultOverallThreadCacheSize = 8u * kMaxThreadCacheSize;
@@ skipping 157 matching lines @@
 static const int kMaxStackDepth = 31;
 struct StackTrace {
   uintptr_t size;          // Size of object
   uintptr_t depth;         // Number of PC values stored in array below
   void*     stack[kMaxStackDepth];
 };
 
 }  // namespace tcmalloc
 
 #endif  // TCMALLOC_COMMON_H_