PM: Add UMA metrics for WorkingSetTrim

Add to simple UMA metrics so we can better track the frequency that working set trim is used.

Bug: b:169771540
Change-Id: I77b9bb5d7bd17207b08513429748e90cc82f6d08
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2441313Reviewed-by: François Doray <fdoray@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Commit-Queue: Brian Geffon <bgeffon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#812464}

chrome/browser/performance_manager/policies/working_set_trimmer_policy.cc

@@ -7,6 +7,7 @@
 #include "base/time/time.h"
 #include "build/build_config.h"
 
+#include "base/metrics/histogram_macros.h"
 #include "base/strings/strcat.h"
 #include "base/strings/string_number_conversions.h"
 #include "chrome/browser/performance_manager/mechanisms/working_set_trimmer.h"
@@ -87,7 +88,11 @@ void WorkingSetTrimmerPolicy::SetLastTrimTime(const ProcessNode* process_node,
 bool WorkingSetTrimmerPolicy::TrimWorkingSet(const ProcessNode* process_node) {
   auto* trimmer = mechanism::WorkingSetTrimmer::GetInstance();
   DCHECK(trimmer);
+
+  static int renderers_trimmed = 0;
   if (process_node->GetProcess().IsValid()) {
+    UMA_HISTOGRAM_COUNTS_10000("Memory.WorkingSetTrim.RendererTrimCount",
+                               ++renderers_trimmed);
     SetLastTrimTimeNow(process_node);
     return trimmer->TrimWorkingSet(process_node);
   }

chrome/browser/performance_manager/policies/working_set_trimmer_policy_chromeos.cc

@@ -5,6 +5,7 @@
 #include "chrome/browser/performance_manager/policies/working_set_trimmer_policy_chromeos.h"
 
 #include "base/bind.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/rand_util.h"
 #include "chrome/browser/chromeos/arc/arc_util.h"
 #include "chrome/browser/chromeos/arc/process/arc_process.h"
@@ -162,6 +163,10 @@ bool WorkingSetTrimmerPolicyChromeOS::IsArcProcessEligibleForReclaim(
 bool WorkingSetTrimmerPolicyChromeOS::TrimArcProcess(base::ProcessId pid) {
   SetArcProcessLastTrimTime(pid, base::TimeTicks::Now());
 
+  static int arc_processes_trimmed = 0;
+  UMA_HISTOGRAM_COUNTS_10000("Memory.WorkingSetTrim.ArcProcessTrimCount",
+                             ++arc_processes_trimmed);
+
   auto* trimmer = static_cast<mechanism::WorkingSetTrimmerChromeOS*>(
       mechanism::WorkingSetTrimmer::GetInstance());
   return trimmer->TrimWorkingSet(pid);

tools/metrics/histograms/histograms_xml/memory/histograms.xml

@@ -2221,6 +2221,26 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   </summary>
 </histogram>
 
+<histogram name="Memory.WorkingSetTrim.ArcProcessTrimCount"
+    units="ProcessesTrimmed" expires_after="M95">
+  <owner>bgeffon@chromium.org</owner>
+  <owner>fdoray@chromium.org</owner>
+  <summary>
+    Cumulative number of ARC processes trimmed during a user's session, recorded
+    each time an ARC process is trimmed. Available on ChromeOS.
+  </summary>
+</histogram>
+
+<histogram name="Memory.WorkingSetTrim.RendererTrimCount"
+    units="RenderersTrimmed" expires_after="M95">
+  <owner>bgeffon@chromium.org</owner>
+  <owner>fdoray@chromium.org</owner>
+  <summary>
+    Cumulative number of renderers trimmed during a user's session, recorded
+    each time a renderer is trimmed. Available on Windows and ChromeOS.
+  </summary>
+</histogram>
+
 <histogram name="MemoryAndroid.DeviceMemoryClass" units="units"
     expires_after="2020-06-07">
   <owner>hajimehoshi@chromium.org</owner>