This creates a field trial to determine the best level for low memory

notification.

It creates a field trial with 7 groups: default (kernel default
value), turning notification off (relying on OOM killer only), 0MB, 25MB, 50MB
margin, 100MB margin, and 200MB margin.

Also, in order to set parameters for the trial, this CL creates
an API for setting the low memory margin.

BUG=chromium-os:20080
TEST=Ran on device several times, checked that the memory margin was
set correctly when the session started, and that different trial groups
were selected.


Review URL: http://codereview.chromium.org/10206029

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@135205 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 29 insertions, 16 deletions

diff --git a/chrome/browser/oom_priority_manager.cc b/chrome/browser/oom_priority_manager.cc
index 0d87d4c..60fa186 100644
--- a/chrome/browser/oom_priority_manager.cc
+++ b/chrome/browser/oom_priority_manager.cc
@@ -10,6 +10,7 @@
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/command_line.h"
+#include "base/metrics/field_trial.h"
 #include "base/metrics/histogram.h"
 #include "base/process.h"
 #include "base/process_util.h"
@@ -51,14 +52,25 @@ namespace browser {
 
 namespace {
 
+// Name of the experiment to run.
+const char kExperiment[] = "LowMemoryMargin";
+
+#define EXPERIMENT_CUSTOM_COUNTS(name, sample, min, max, buckets)          \
+    UMA_HISTOGRAM_CUSTOM_COUNTS(name, sample, min, max, buckets);          \
+    if (base::FieldTrialList::TrialExists(kExperiment))                    \
+      UMA_HISTOGRAM_CUSTOM_COUNTS(                                         \
+          base::FieldTrial::MakeName(name, kExperiment),                   \
+          sample, min, max, buckets);
+
 // Record a time in seconds, over a potential interval of about a day. Must be a
 // macro and not a function because the histograms system requires a unique
 // static variable at the site of each call.
-#define UMA_HISTOGRAM_SECONDS(name, sample) UMA_HISTOGRAM_CUSTOM_COUNTS( \
-    name, sample, 1, 10000, 50)
+#define EXPERIMENT_HISTOGRAM_SECONDS(name, sample)                         \
+    EXPERIMENT_CUSTOM_COUNTS(name, sample, 1, 10000, 50)
+
 // Record a size in megabytes, over a potential interval up to 32 GB.
-#define UMA_HISTOGRAM_MEGABYTES(name, sample) UMA_HISTOGRAM_CUSTOM_COUNTS( \
-    name, sample, 1, 32768, 50)
+#define EXPERIMENT_HISTOGRAM_MEGABYTES(name, sample)                       \
+    EXPERIMENT_CUSTOM_COUNTS(name, sample, 1, 32768, 50)
 
 // The default interval in seconds after which to adjust the oom_score_adj
 // value.
@@ -241,11 +253,11 @@ bool OomPriorityManager::DiscardTabById(int64 target_web_contents_id) {
 void OomPriorityManager::RecordDiscardStatistics() {
   // Record a raw count so we can compare to discard reloads.
   discard_count_++;
-  UMA_HISTOGRAM_CUSTOM_COUNTS(
-      "Tabs.Discard.DiscardCount", discard_count_, 1, 1000, 50);
+  EXPERIMENT_CUSTOM_COUNTS("Tabs.Discard.DiscardCount",
+                           discard_count_, 1, 1000, 50);
 
   // TODO(jamescook): Maybe incorporate extension count?
-  UMA_HISTOGRAM_COUNTS_100("Tabs.Discard.TabCount", GetTabCount());
+  EXPERIMENT_CUSTOM_COUNTS("Tabs.Discard.TabCount", GetTabCount(), 1, 100, 50);
 
   // TODO(jamescook): If the time stats prove too noisy, then divide up users
   // based on how heavily they use Chrome using tab count as a proxy.
@@ -254,23 +266,24 @@ void OomPriorityManager::RecordDiscardStatistics() {
     // This is the first discard this session.
     TimeDelta interval = TimeTicks::Now() - start_time_;
     int interval_seconds = static_cast<int>(interval.InSeconds());
-    UMA_HISTOGRAM_SECONDS("Tabs.Discard.InitialTime", interval_seconds);
+    EXPERIMENT_HISTOGRAM_SECONDS("Tabs.Discard.InitialTime", interval_seconds);
   } else {
     // Not the first discard, so compute time since last discard.
     TimeDelta interval = TimeTicks::Now() - last_discard_time_;
     int interval_seconds = static_cast<int>(interval.InSeconds());
-    UMA_HISTOGRAM_SECONDS("Tabs.Discard.IntervalTime", interval_seconds);
+    EXPERIMENT_HISTOGRAM_SECONDS("Tabs.Discard.IntervalTime", interval_seconds);
   }
   // Record Chrome's concept of system memory usage at the time of the discard.
   base::SystemMemoryInfoKB memory;
   if (base::GetSystemMemoryInfo(&memory)) {
-    int mem_anonymous_kb = memory.active_anon + memory.inactive_anon;
-    UMA_HISTOGRAM_MEGABYTES("Tabs.Discard.MemAnonymousMB",
-                            mem_anonymous_kb / 1024);
-    int mem_available_kb =
-        memory.active_file + memory.inactive_file + memory.free;
-    UMA_HISTOGRAM_MEGABYTES("Tabs.Discard.MemAvailableMB",
-                            mem_available_kb / 1024);
+    int mem_anonymous_mb = (memory.active_anon + memory.inactive_anon) / 1024;
+    EXPERIMENT_HISTOGRAM_MEGABYTES("Tabs.Discard.MemAnonymousMB",
+                                   mem_anonymous_mb);
+
+    int mem_available_mb =
+        (memory.active_file + memory.inactive_file + memory.free) / 1024;
+    EXPERIMENT_HISTOGRAM_MEGABYTES("Tabs.Discard.MemAvailableMB",
+                                   mem_available_mb);
   }
   // Set up to record the next interval.
   last_discard_time_ = TimeTicks::Now();