Fix free memory calculation.

base/process/process_metrics_win.cc

Index: base/process/process_metrics_win.cc
diff --git a/base/process/process_metrics_win.cc b/base/process/process_metrics_win.cc
index d2f0c935531071a092289637b9696a744c22ea9a..a9f7762dad637355694adfc32b7291dc47892942 100644
--- a/base/process/process_metrics_win.cc
+++ b/base/process/process_metrics_win.cc
@@ -23,6 +23,21 @@ namespace {
 // System pagesize. This value remains constant on x86/64 architectures.
 const int PAGESIZE_KB = 4;
 
+typedef enum _SYSTEM_INFORMATION_CLASS {
+  SystemMemoryListInformation = 80
+} SYSTEM_INFORMATION_CLASS;
+
+struct SYSTEM_MEMORY_LIST_INFORMATION {
+  SIZE_T ZeroPageCount;
+  SIZE_T FreePageCount;
+  SIZE_T ModifiedPageCount;
+  SIZE_T ModifiedNoWritePageCount;
+  SIZE_T BadPageCount;
+  SIZE_T PageCountByPriority[8];
+  SIZE_T RepurposedPagesByPriority[8];
+  SIZE_T ModifiedPageCountPageFile;
+};
+
 typedef NTSTATUS(WINAPI* NTQUERYSYSTEMINFORMATION)(
     SYSTEM_INFORMATION_CLASS SystemInformationClass,
     PVOID SystemInformation,
@@ -32,7 +47,7 @@ typedef NTSTATUS(WINAPI* NTQUERYSYSTEMINFORMATION)(
 }  // namespace
 
 SystemMemoryInfoKB::SystemMemoryInfoKB()
-    : total(0), free(0), swap_total(0), swap_free(0) {}
+    : total(0), free(0), zero(0), available(0), swap_total(0), swap_free(0) {}
 
 SystemMemoryInfoKB::SystemMemoryInfoKB(const SystemMemoryInfoKB& other) =
     default;
@@ -349,17 +364,36 @@ size_t GetPageSize() {
 // This function uses the following mapping between MEMORYSTATUSEX and
 // SystemMemoryInfoKB:
 //   ullTotalPhys ==> total
-//   ullAvailPhys ==> free
+//   ullAvailPhys ==> available
 //   ullTotalPageFile ==> swap_total
 //   ullAvailPageFile ==> swap_free
 bool GetSystemMemoryInfo(SystemMemoryInfoKB* meminfo) {
+  // Get the function pointer.
+  static const NTQUERYSYSTEMINFORMATION query_sys_info =
+      reinterpret_cast<NTQUERYSYSTEMINFORMATION>(::GetProcAddress(
+          GetModuleHandle(L"ntdll.dll"), "NtQuerySystemInformation"));
+
+  if (query_sys_info != nullptr) {
+    SYSTEM_MEMORY_LIST_INFORMATION mem_list_info = {};
+    ULONG ret_length = 0;
+    NTSTATUS status =
+        query_sys_info(SystemMemoryListInformation, &mem_list_info,
+                       sizeof(mem_list_info), &ret_length);
+    if (NT_SUCCESS(status)) {
+      meminfo->zero = mem_list_info.ZeroPageCount * PAGESIZE_KB;
+      meminfo->free = mem_list_info.FreePageCount * PAGESIZE_KB;
+    } else {
+      NOTREACHED() << "status = " << (ULONG)status << ", ret_length = " << ret_length;
+    }
+  }
+
   MEMORYSTATUSEX mem_status;
   mem_status.dwLength = sizeof(mem_status);
   if (!::GlobalMemoryStatusEx(&mem_status))
     return false;
 
   meminfo->total = mem_status.ullTotalPhys / 1024;
-  meminfo->free = mem_status.ullAvailPhys / 1024;
+  meminfo->available = mem_status.ullAvailPhys / 1024;
   meminfo->swap_total = mem_status.ullTotalPageFile / 1024;
   meminfo->swap_free = mem_status.ullAvailPageFile / 1024;