Record swap metrics

content/browser/memory/swap_metrics_observer_mac.cc

Index: content/browser/memory/swap_metrics_observer_mac.cc
diff --git a/content/browser/memory/swap_metrics_observer_mac.cc b/content/browser/memory/swap_metrics_observer_mac.cc
new file mode 100644
index 0000000000000000000000000000000000000000..d44b50fe543b11a7d633a3ed138595239157e837
--- /dev/null
+++ b/content/browser/memory/swap_metrics_observer_mac.cc
@@ -0,0 +1,15 @@
+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "content/browser/memory/swap_metrics_observer.h"
+
+namespace content {
+
+// static
+SwapMetricsObserver* SwapMetricsObserver::GetInstance() {
+  // TODO(bashi): Implement SwapMetricsObserver for macOS.

[erikchen, 2017/04/18 17:48:19]

You'll want to use host_statistics64.

See xnu-3789.1.32/osfmk/kern/host.c:524, available at
https://opensource.apple.com/release/macos-1012.html

Relevant stats:

 607       stat->compressions = host_vm_stat.compressions;                      
    
 608       stat->decompressions = host_vm_stat.decompressions;                  
    
 609       stat->swapins = host_vm_stat.swapins;                                
    
 610       stat->swapouts = host_vm_stat.swapouts;                              
    
...
618       stat->total_uncompressed_pages_in_compressor =
c_segment_pages_compressed;
 
Keep in mind that macOS uses both a compressor and swap. The basic structure is:
resident memory <--can be compressed/decompressed--> compressed memory . <--can
be swapped/unswapped--> swap

[bashi, 2017/04/20 01:32:04]

Thanks for detailed info! Using host_statistics64 is the plan and I'm aware of
macOS uses both compression and swap. I'm planning to implement it in follow-up
CLs if the overall approach is reasonable.

+  return nullptr;
+}
+
+}  // namespace content