Record swap metrics

content/browser/memory/swap_metrics_observer_linux.cc

+// 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_linux.h"
+
+#include "base/metrics/histogram_macros.h"
+#include "base/process/process_metrics.h"
+
+namespace content {
+
+// static
+SwapMetricsObserver* SwapMetricsObserver::GetInstance() {
+  return SwapMetricsObserverLinux::GetInstance();
+}
+
+// static
+SwapMetricsObserverLinux* SwapMetricsObserverLinux::GetInstance() {
+  return base::Singleton<

[Primiano Tucci (use gerrit), 2017/04/27 10:01:20]

IWYU (+base/singleton.h).
BTW these days you can just use static locals, as they are thread-safe in c++11,
i..e

static SwapMemoryObserverLinux* instance = new SwapMemoryObserverLinux();
return instance.

The alternative I learned from dcheng@ is using base::LazyInstance, which is
more efficient: it doesnt cause a new (conversely to both singleton and the
static local) and allocates directly the instance from static storage in bzz,
hence reducing the indirection layers involved.

[bashi, 2017/04/28 02:05:35]

Changed to use static local. Thanks for the info!

+      SwapMetricsObserverLinux,
+      base::LeakySingletonTraits<SwapMetricsObserverLinux>>::get();
+}
+
+SwapMetricsObserverLinux::SwapMetricsObserverLinux() {}
+
+SwapMetricsObserverLinux::~SwapMetricsObserverLinux() {}
+
+void SwapMetricsObserverLinux::UpdateMetricsInternal(base::TimeDelta interval) {
+  base::SystemMemoryInfoKB memory_info;
+  if (!base::GetSystemMemoryInfo(&memory_info))
+    return;
+
+  // Don't record metrics when the system doesn't seem to have swap.
+  if (memory_info.pswpin == 0)
+    return;

[Primiano Tucci (use gerrit), 2017/04/27 10:01:20]

maybe also stop the timer in these failure cases? 

[bashi, 2017/04/28 02:05:35]

Yes. Probably we shouldn't start the timer in the first place when these fails.
Added checks.

+
+  double in_counts = memory_info.pswpin - last_pswpin_;
+  double out_counts = memory_info.pswpout - last_pswpout_;
+  last_pswpin_ = memory_info.pswpin;
+  last_pswpout_ = memory_info.pswpout;
+
+  if (interval.is_zero())
+    return;
+
+  UMA_HISTOGRAM_COUNTS_10000("Memory.Experimental.SwapInPerSecond",
+                             in_counts / interval.InSecondsF());
+  UMA_HISTOGRAM_COUNTS_10000("Memory.Experimental.SwapOutPerSecond",
+                             out_counts / interval.InSecondsF());
+}
+
+}  // namespace content