Add support for CountResidentBytes in windows

base/trace_event/process_memory_dump.cc

Index: base/trace_event/process_memory_dump.cc
diff --git a/base/trace_event/process_memory_dump.cc b/base/trace_event/process_memory_dump.cc
index ae60bb06b152639c0e80ab2226a6a96b65699351..76da89d433a81eb780617ccc746cd9113fe6bb89 100644
--- a/base/trace_event/process_memory_dump.cc
+++ b/base/trace_event/process_memory_dump.cc
@@ -16,6 +16,10 @@
 #include <sys/mman.h>
 #endif
 
+#if defined(OS_WIN)
+#include <Psapi.h>
+#endif
+
 namespace base {
 namespace trace_event {
 
@@ -45,28 +49,43 @@ size_t ProcessMemoryDump::CountResidentBytes(void* start_address,
   const size_t kMaxChunkSize = 32 * 1024 * 1024;
   size_t offset = 0;
   size_t total_resident_size = 0;
-  int result = 0;
+  int result = 0;  // 0 on success.

[brucedawson, 2016/01/19 20:16:43]

Reusing "int result" as a success/error code across three platforms is probably
stretching it a bit. Perhaps better to have "bool failure = false;" and then
remap the mincore/QueryWorkingSetEx failure codes to that more obvious type.

[ssid, 2016/01/20 13:03:59]

Done.

   while (offset < mapped_size) {
-    void* chunk_start = reinterpret_cast<void*>(start_pointer + offset);
+    uintptr_t chunk_start = (start_pointer + offset);
     const size_t chunk_size = std::min(mapped_size - offset, kMaxChunkSize);
     const size_t page_count = (chunk_size + page_size - 1) / page_size;
     size_t resident_page_count = 0;
 
 #if defined(OS_MACOSX) || defined(OS_IOS)
-    std::vector<char> vec(page_count + 1);
+    std::vector<char> vec(page_count);
     // mincore in MAC does not fail with EAGAIN.
-    result = mincore(chunk_start, chunk_size, vec.data());
+    result =
+        mincore(reinterpret_cast<void*>(chunk_start), chunk_size, vec.data());
     if (result)
       break;
 
     for (size_t i = 0; i < page_count; i++)
       resident_page_count += vec[i] & MINCORE_INCORE ? 1 : 0;
+#elif defined(OS_WIN)
+    std::vector<PSAPI_WORKING_SET_EX_INFORMATION> vec(page_count);

[brucedawson, 2016/01/19 20:16:43]

Possibly out of scope for this change, but the std::vector should really be
allocated *outside* of the loop, to avoid reallocating it each time.

It's also worth thinking about using a local variable array instead of
std::vector to avoid allocating any memory. With kMaxChunkSize set to 32 MB that
would give us a 8K element array (probably 128 KB on 64-bit) which is large but
not totally nuts. kMaxChunkSize could be reduced on Windows to minimize the size
of the array, but knowing whether that was worthwhile would require profiling
QueryWorkingSetEx.

[ssid, 2016/01/20 13:03:59]

I will add a follow up to this CL.

+    for (size_t i = 0; i < page_count; i++) {
+      vec[i].VirtualAddress =
+          reinterpret_cast<void*>(chunk_start + i * page_size);
+    }
+    DWORD vec_size = static_cast<DWORD>(
+        page_count * sizeof(PSAPI_WORKING_SET_EX_INFORMATION));
+    result = !QueryWorkingSetEx(GetCurrentProcess(), vec.data(), vec_size);
+    if (result)
+      break;
+    for (size_t i = 0; i < page_count; i++)
+      resident_page_count += vec[i].VirtualAttributes.Valid;
 #else   // defined(OS_MACOSX) || defined(OS_IOS)

[brucedawson, 2016/01/19 20:16:43]

This comment is no longer meaningful. Consider changing this to #elif
defined(???) instead of just a fall-through.

[ssid, 2016/01/20 13:03:59]

Done.

-    std::vector<unsigned char> vec(page_count + 1);
+    std::vector<unsigned char> vec(page_count);
     int error_counter = 0;
     // HANDLE_EINTR tries for 100 times. So following the same pattern.
     do {
-      result = mincore(chunk_start, chunk_size, vec.data());
+      result =
+          mincore(reinterpret_cast<void*>(chunk_start), chunk_size, vec.data());
     } while (result == -1 && errno == EAGAIN && error_counter++ < 100);
     if (result)
       break;