Thu Sep 10 13:51:15 2009 Google Inc. <opensource@google.com>

	* google-perftools: version 1.4 release
	* Add debugallocation library, to catch memory leaks, stomping, etc
	* Add --raw mode to allow for delayed processing of pprof files
	* Use less memory when reading CPU profiles
	* New environment variables to control kernel-allocs (sbrk, memfs, etc)
	* Add MarkThreadBusy(): performance improvement
	* Remove static thread-cache-size code; all is dynamic now
	* Add new HiddenPointer class to heap checker
	* BUGFIX: pvalloc(0) allocates now (found by new debugalloc library)
	* BUGFIX: valloc test (not implementation) no longer overruns memory
	* BUGFIX: GetHeapProfile no longer deadlocks
	* BUGFIX: Support unmapping memory regions before main
	* BUGFIX: Fix some malloc-stats formatting
	* BUGFIX: Don't crash as often when freeing libc-allocated memory
	* BUGFIX: Deal better with incorrect PPROF_PATH when symbolizing
	* BUGFIX: weaken new/delete/etc in addition to malloc/free/etc
	* BUGFIX: Fix return value of GetAllocatedSize
	* PORTING: Fix mmap-#define problem on some 64-bit systems
	* PORTING: Call ranlib again (some OS X versions need it)
	* PORTING: Fix a leak when building with LLVM
	* PORTING: Remove some unneeded bash-ishs from testing scripts
	* WINDOWS: Support library unloading as well as loading
	* WINDOWS/BUGFIX: Set page to 'xrw' instead of 'rw' when patching


git-svn-id: http://gperftools.googlecode.com/svn/trunk@76 6b5cf1ce-ec42-a296-1ba9-69fdba395a50

1 files changed, 11 insertions, 15 deletions

diff --git a/src/common.cc b/src/common.cc
index d89ba83..04723b1 100644
--- a/src/common.cc
+++ b/src/common.cc
@@ -58,21 +58,17 @@ int SizeMap::NumMoveSize(size_t size) {
   // Use approx 64k transfers between thread and central caches.
   int num = static_cast<int>(64.0 * 1024.0 / size);
   if (num < 2) num = 2;
-  // Clamp well below kMaxFreeListLength to avoid ping pong between central
-  // and thread caches.
-  if (num > static_cast<int>(0.8 * kMaxFreeListLength))
-    num = static_cast<int>(0.8 * kMaxFreeListLength);
-
-  // Also, avoid bringing in too many objects into small object free
-  // lists.  There are lots of such lists, and if we allow each one to
-  // fetch too many at a time, we end up having to scavenge too often
-  // (especially when there are lots of threads and each thread gets a
-  // small allowance for its thread cache).  This fixes a problem seen
-  // in the 20060502 bigtable release by both Andrew Fikes and Ben
-  // Darnell.
-  //
-  // TODO: Make thread cache free list sizes dynamic so that we do not
-  // have to equally divide a fixed resource amongst lots of threads.
+
+  // Avoid bringing too many objects into small object free lists.
+  // If this value is too large:
+  // - We waste memory with extra objects sitting in the thread caches.
+  // - The central freelist holds its lock for too long while
+  //   building a linked list of objects, slowing down the allocations
+  //   of other threads.
+  // If this value is too small:
+  // - We go to the central freelist too often and we have to acquire
+  //   its lock each time.
+  // This value strikes a balance between the constraints above.
   if (num > 32) num = 32;
 
   return num;