Dump /proc/<pid>/maps with every heap profile dump.

third_party/tcmalloc/chromium/src/deep-heap-profile.cc

Index: third_party/tcmalloc/chromium/src/deep-heap-profile.cc
diff --git a/third_party/tcmalloc/chromium/src/deep-heap-profile.cc b/third_party/tcmalloc/chromium/src/deep-heap-profile.cc
index 3577d04c92989b60bc4848ea31b70e96df744bed..ef73ff09e4774cd131b044cb8a6b84499be07ba3 100644
--- a/third_party/tcmalloc/chromium/src/deep-heap-profile.cc
+++ b/third_party/tcmalloc/chromium/src/deep-heap-profile.cc
@@ -91,8 +91,11 @@ int DeepHeapProfile::FillOrderedProfile(char buffer[], int buffer_size) {
     }
 
     // Write maps into a .maps file with using the global buffer.
-    WriteMapsToFile(filename_prefix_, kProfilerBufferSize, profiler_buffer_);
+    WriteMapsToFile(filename_prefix_, 0,

[Alexander Potapenko, 2012/08/14 08:39:57]

Why is this 0?
If the process didn't call exec() you're going to have the same memory mappings
and the same allocation history after fork(), so the only thing you need to do
is to reopen the correct /proc/<pid>/maps.

[Dai Mikurube (NOT FULLTIME), 2012/08/14 09:33:26]

Data in /proc/<pid>/maps is used in this dumper "deep-heap-profile", and in the
post-mortem analyzer script "dmprof".  dmprof expects a set of files for a
Chrome process:

* prefix.<pid>.maps: maps when the process started or forked
* prefix.<pid>.<nnnn>.heap: heap profile dumps
* prefix.<pid>.<nnnn>.buckets: bucket lists

To make it easy to manage all files for one process, deep-heap-profile has
dumped "maps" in the beginning of every process.  (We can copy required files by
"prefix.<pid>.*".)


By this change, deep-heap-profile dumps "maps" for every request in addition to
one in the beginning of the process.  It is to understand memory mapping history
of the process.

We will have the following "maps" files :

* prefix.<pid>.maps: maps when the process started or forked
* prefix.<pid>.<nnnn>.maps: maps when requested to dump

"0" for WriteMapsToFile is for the former.

[Alexander Potapenko, 2012/08/14 09:36:47]

Can you please prepend a comment to "0" so that the reader could understand what
this parameter stands for? (Because zero count has a special meaning, it may be
better to note that)

+                    kProfilerBufferSize, profiler_buffer_);
   }
+  WriteMapsToFile(filename_prefix_, dump_count_,

[Alexander Potapenko, 2012/08/14 08:39:57]

Are you going to write the mappings twice if most_recent_pid_ != getpid()?

[Dai Mikurube (NOT FULLTIME), 2012/08/14 09:33:26]

Yes, I know normally "prefix.<pid>.maps" and "prefix.<pid>.0001.maps" will be
same.

Some existing scripts assume "prefix.<pid>.maps".  I'd like to dump both for a
while for compatibility.  (Will remove the former.)

I think it is not a large problem since "maps" is not large.

+                  kProfilerBufferSize, profiler_buffer_);
 
   // Reset committed sizes of buckets.
   ResetCommittedSize(deep_table_);
@@ -323,11 +326,18 @@ size_t DeepHeapProfile::GetCommittedSize(
 
 // static
 void DeepHeapProfile::WriteMapsToFile(const char* filename_prefix,
+                                      unsigned count,
                                       int buffer_size,
                                       char buffer[]) {
   char filename[100];
-  snprintf(filename, sizeof(filename),
-           "%s.%05d.maps", filename_prefix, static_cast<int>(getpid()));
+  if (count > 0) {
+    snprintf(filename, sizeof(filename),
+             "%s.%05d.%04d.maps", filename_prefix, static_cast<int>(getpid()),
+             count);
+  } else {
+    snprintf(filename, sizeof(filename),
+             "%s.%05d.maps", filename_prefix, static_cast<int>(getpid()));
+  }
 
   RawFD maps_fd = RawOpenForWriting(filename);
   RAW_DCHECK(maps_fd != kIllegalRawFD, "");