Fix free memory calculation.

base/process/process_metrics_mac.cc

Index: base/process/process_metrics_mac.cc
diff --git a/base/process/process_metrics_mac.cc b/base/process/process_metrics_mac.cc
index a3c2d6a14aa6acbd2e07e9afd6a55a836bbb3f10..74c9c0aa1f795d2ab1b971149a9c76a89d1c75c0 100644
--- a/base/process/process_metrics_mac.cc
+++ b/base/process/process_metrics_mac.cc
@@ -80,11 +80,6 @@ bool IsAddressInSharedRegion(mach_vm_address_t addr, cpu_type_t type) {
 
 }  // namespace
 
-SystemMemoryInfoKB::SystemMemoryInfoKB() : total(0), free(0) {}
-
-SystemMemoryInfoKB::SystemMemoryInfoKB(const SystemMemoryInfoKB& other) =
-    default;
-
 // Getting a mach task from a pid for another process requires permissions in
 // general, so there doesn't really seem to be a way to do these (and spinning
 // up ps to fetch each stats seems dangerous to put in a base api for anyone to
@@ -377,7 +372,6 @@ size_t GetSystemCommitCharge() {
   return (data.active_count * PAGE_SIZE) / 1024;
 }
 
-// On Mac, We only get total memory and free memory from the system.
 bool GetSystemMemoryInfo(SystemMemoryInfoKB* meminfo) {
   struct host_basic_info hostinfo;
   mach_msg_type_number_t count = HOST_BASIC_INFO_COUNT;
@@ -390,17 +384,24 @@ bool GetSystemMemoryInfo(SystemMemoryInfoKB* meminfo) {
   DCHECK_EQ(HOST_BASIC_INFO_COUNT, count);
   meminfo->total = static_cast<int>(hostinfo.max_mem / 1024);
 
-  vm_statistics_data_t vm_info;
-  count = HOST_VM_INFO_COUNT;
+  vm_statistics64_data_t vm_info;
+  count = HOST_VM_INFO64_COUNT;
 
-  if (host_statistics(host.get(), HOST_VM_INFO,
-                      reinterpret_cast<host_info_t>(&vm_info),
-                      &count) != KERN_SUCCESS) {
+  if (host_statistics64(host.get(), HOST_VM_INFO64,
+                        reinterpret_cast<host_info64_t>(&vm_info),
+                        &count) != KERN_SUCCESS) {
     return false;
   }
+  DCHECK_EQ(HOST_VM_INFO64_COUNT, count);
 
   meminfo->free = static_cast<int>(
       (vm_info.free_count - vm_info.speculative_count) * PAGE_SIZE / 1024);
+  meminfo->speculative =
+      static_cast<int>(vm_info.speculative_count * PAGE_SIZE / 1024);

[danakj, 2017/03/10 17:13:48]

should these fields on meminfo not be int64? if not..

should these all be saturated_cast? or checked_cast? should we encourage it to
not overflow by doing the division step first? or does the compiler do the right
thing?

[Michael K. (Yandex Team), 2017/03/10 18:22:37]

meminfo contains data in kilobytes. So it is hard to imagine that ordinary "int"
isn't enough.

What about safe casts... vm_info's fields are unsigned 32bit. And multiplying by
4k page size ... It's  easy to overflow(
Doing the division step first isn't right (3 * 4k / 1k != 3 / 1k * 4k)
It's better do PAGE_SIZE / 1024 * value.
With the assumption that PAGE_SIZE is divisible by 1024.

Done.
 

+  meminfo->file_backed =
+      static_cast<int>(vm_info.external_page_count * PAGE_SIZE / 1024);
+  meminfo->purgeable =
+      static_cast<int>(vm_info.purgeable_count * PAGE_SIZE / 1024);
 
   return true;
 }