Enable UMA histogram logger for low memor kill events in ArcMetricsService.

components/arc/metrics/arc_low_memory_killer_monitor.cc

 // Copyright 2016 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 "chrome/browser/chromeos/arc/arc_low_memory_killer_monitor.h"
+#include "components/arc/metrics/arc_low_memory_killer_monitor.h"
 
 #include <errno.h>
 #include <fcntl.h>
 #include <stdio.h>
 
 #include <vector>
 
 #include "base/bind.h"
 #include "base/files/file_util.h"
 #include "base/location.h"
@@ skipping 49 matching lines @@
   }
   // Skip kernel messages prior to the instantiation of this object to avoid
   // double reporting.
   fseek(kmsg_handle, 0, SEEK_END);
 
   char buf[kMaxBufSize];
   int freed_size;
   int64_t timestamp, last_timestamp = -1;
   const TimeDelta kMaxTimeDelta =
       TimeDelta::FromSeconds(MAX_LOWMEMORYKILL_TIME_SECS);
+  int oom_kills = 0;
 
   while (fgets(buf, kMaxBufSize, kmsg_handle)) {
     if (worker_pool->IsShutdownInProgress()) {
       DVLOG(1) << "Chrome is shutting down, exit now.";
       break;
     }
     if (RE2::PartialMatch(buf, "lowmemorykiller: .* to free (\\d+)kB",
                           &freed_size)) {
       std::vector<StringPiece> fields = SplitStringPiece(
           buf, ",", base::TRIM_WHITESPACE, base::SPLIT_WANT_ALL);
 
       // The time to last kill event. Could be |kMaxTimeDelta| in case of the
       // first kill event.
       TimeDelta time_delta(kMaxTimeDelta);
       // Timestamp is the third field in a line of /dev/kmsg.
       //
       // Sample log line:
       // 6,2302,533604004,-;lowmemorykiller: Killing 'externalstorage' (21742),
       // adj 1000,\x0a   to free 27320kB on behalf of 'kswapd0' (47) because\x0a
       // cache 181920kB is below limit 184320kB for oom_score_adj 1000\x0a
       // Free memory is 1228kB above reserved
       if (fields.size() >= 3) {
         base::StringToInt64(fields[2], &timestamp);
         if (last_timestamp > 0) {
           time_delta = TimeDelta::FromMicroseconds(timestamp - last_timestamp);
         }
         last_timestamp = timestamp;
+        UMA_HISTOGRAM_LOWMEMORYKILL_TIMES(
+            "Arc.LowMemoryKiller.TimeDelta", time_delta);
 
-        UMA_HISTOGRAM_MEMORY_KB("ArcRuntime.LowMemoryKiller.FreedSize",
+        ++oom_kills;
+        UMA_HISTOGRAM_CUSTOM_COUNTS(

[hidehiko, 2016/03/24 08:11:21]

Shouldn't this be out of the while loop?
If it is intentional to count less values than final oom_kills value, it's nice
to comment why.

[cylee1, 2016/03/24 14:36:06]

Yes it's intentional. One of the reason is this dedicated loop may not exit when
shutting down chrome because of the blocking fgets(). As a workaround a
cumulative count should be acceptable. The existing metric
"Tabs.SadTab.KillCreated.OOM" is also cumulative.

+            "Arc.LowMemoryKiller.Count", oom_kills, 1, 1000, 1001);
+
+        UMA_HISTOGRAM_MEMORY_KB("Arc.LowMemoryKiller.FreedSize",
                                 freed_size);
-        UMA_HISTOGRAM_LOWMEMORYKILL_TIMES(
-            "ArcRuntime.LowMemoryKiller.TimeDelta", time_delta);
       }
     }
   }
   base::CloseFile(kmsg_handle);
 }
 
 }  // namespace arc