Tag Mac VM regions allocated by V8. This has no effect other than making it possi...

src/platform-macos.cc

Index: src/platform-macos.cc
===================================================================
--- src/platform-macos.cc	(revision 2953)
+++ src/platform-macos.cc	(working copy)
@@ -42,6 +42,7 @@
 #include <mach/mach.h>
 #include <mach/semaphore.h>
 #include <mach/task.h>
+#include <mach/vm_statistics.h>
 #include <sys/time.h>
 #include <sys/resource.h>
 #include <sys/types.h>
@@ -128,7 +129,12 @@
                    bool is_executable) {
   const size_t msize = RoundUp(requested, getpagesize());
   int prot = PROT_READ | PROT_WRITE | (is_executable ? PROT_EXEC : 0);
-  void* mbase = mmap(NULL, msize, prot, MAP_PRIVATE | MAP_ANON, -1, 0);
+  // Use the fd parameter to pass vm_alloc flags to tag the region with the
+  // user-defined tag 255. This helps identify V8-allocated regions in memory
+  // analysis tools like vmmap(1).
+  void* mbase = mmap(NULL, msize, prot,
+                     MAP_PRIVATE | MAP_ANON,
+                     VM_MAKE_TAG(255), 0);
   if (mbase == MAP_FAILED) {
     LOG(StringEvent("OS::Allocate", "mmap failed"));
     return NULL;
@@ -195,8 +201,9 @@
   FILE* file = fopen(name, "w+");
   if (file == NULL) return NULL;
   fwrite(initial, size, 1, file);
-  void* memory =
-      mmap(0, size, PROT_READ | PROT_WRITE, MAP_SHARED, fileno(file), 0);
+  void* memory = mmap(0, size, PROT_READ | PROT_WRITE,
+                      MAP_SHARED,
+                      fileno(file), 0);
   return new PosixMemoryMappedFile(file, memory, size);
 }
 
@@ -280,14 +287,18 @@
 }
 
 
-// Constants used for mmap.
-static const int kMmapFd = -1;
+// Constants used for mmap calls by the VirtualMemory class.
+// kMmapFd is used to pass vm_alloc flags to tag the region with the user
+// defined tag 254. This helps identify V8-allocated regions in memory analysis
+// tools like vmmap(1).
+static const int kMmapFlags = MAP_PRIVATE | MAP_ANON;
+static const int kMmapFd = VM_MAKE_TAG(254);
 static const int kMmapFdOffset = 0;
 
 
 VirtualMemory::VirtualMemory(size_t size) {
   address_ = mmap(NULL, size, PROT_NONE,
-                  MAP_PRIVATE | MAP_ANON | MAP_NORESERVE,
+                  kMmapFlags | MAP_NORESERVE,
                   kMmapFd, kMmapFdOffset);
   size_ = size;
 }
@@ -308,7 +319,7 @@
 bool VirtualMemory::Commit(void* address, size_t size, bool is_executable) {
   int prot = PROT_READ | PROT_WRITE | (is_executable ? PROT_EXEC : 0);
   if (MAP_FAILED == mmap(address, size, prot,
-                         MAP_PRIVATE | MAP_ANON | MAP_FIXED,
+                         kMmapFlags | MAP_FIXED,
                          kMmapFd, kMmapFdOffset)) {
     return false;
   }
@@ -320,7 +331,7 @@
 
 bool VirtualMemory::Uncommit(void* address, size_t size) {
   return mmap(address, size, PROT_NONE,
-              MAP_PRIVATE | MAP_ANON | MAP_NORESERVE | MAP_FIXED,
+              kMmapFlags | MAP_NORESERVE | MAP_FIXED,
               kMmapFd, kMmapFdOffset) != MAP_FAILED;
 }