Actually on Windows VirtualAlloc'ated address might have bigger alignment tha...

third_party/tcmalloc/port.cc

Index: third_party/tcmalloc/port.cc
===================================================================
--- third_party/tcmalloc/port.cc	(revision 26805)
+++ third_party/tcmalloc/port.cc	(working copy)
@@ -71,7 +71,8 @@
   if (pagesize == 0) {
     SYSTEM_INFO system_info;
     GetSystemInfo(&system_info);
-    pagesize = system_info.dwPageSize;
+    pagesize = std::max(system_info.dwPageSize,
+                        system_info.dwAllocationGranularity);
   }
   return pagesize;
 }
@@ -188,17 +189,19 @@
 // munmap's in the middle of the page, which is forbidden in windows.
 extern void* TCMalloc_SystemAlloc(size_t size, size_t *actual_size,
                                   size_t alignment) {
-  // Safest is to make actual_size same as input-size.
-  if (actual_size) {
-    *actual_size = size;
-  }
-
   SpinLockHolder sh(&alloc_lock);
   // Align on the pagesize boundary
   const int pagesize = getpagesize();
   if (alignment < pagesize) alignment = pagesize;
   size = ((size + alignment - 1) / alignment) * alignment;
 
+  // Safest is to make actual_size same as input-size.
+  // TODO(antonm): proper processing of alignments
+  // in actual_size and decommitting.
+  if (actual_size) {
+    *actual_size = size;
+  }
+
   // Ask for extra memory if alignment > pagesize
   size_t extra = 0;
   if (alignment > pagesize) {