ArcLowMemoryKillerMonitor:

chrome/browser/chromeos/arc/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 <fcntl.h>
+#include <vector>
+
+#include "base/bind.h"
+#include "base/location.h"
+#include "base/logging.h"
+#include "base/metrics/histogram_macros.h"
+#include "base/sequenced_task_runner.h"
+#include "base/strings/string_number_conversions.h"
+#include "base/strings/string_split.h"
+#include "base/time/time.h"
+#include "third_party/re2/src/re2/re2.h"
+
+namespace arc {
+
+using base::SequencedWorkerPool;
+using base::StringPiece;
+using base::TimeDelta;
+
+#define MAX_LOWMEMORYKILL_TIME_SECS 30
+#define UMA_HISTOGRAM_LOWMEMORYKILL_TIMES(name, sample) \
+    UMA_HISTOGRAM_CUSTOM_TIMES( \
+        name, sample, base::TimeDelta::FromMilliseconds(1), \
+        base::TimeDelta::FromSeconds(MAX_LOWMEMORYKILL_TIME_SECS), 50)
+
+ArcLowMemoryKillerMonitor::ArcLowMemoryKillerMonitor()
+    : worker_pool_(
+        new SequencedWorkerPool(1, "arc_low_memory_killer_monitor")),
+      weak_ptr_factory_(this) {}
+
+ArcLowMemoryKillerMonitor::~ArcLowMemoryKillerMonitor() {
+  Stop();
+}
+
+void ArcLowMemoryKillerMonitor::Start() {
+  auto task_runner = worker_pool_->GetTaskRunnerWithShutdownBehavior(
+      SequencedWorkerPool::CONTINUE_ON_SHUTDOWN);
+  task_runner->PostTask(
+      FROM_HERE,
+      base::Bind(&ArcLowMemoryKillerMonitor::Run,
+                 weak_ptr_factory_.GetWeakPtr()));
+}
+
+void ArcLowMemoryKillerMonitor::Stop() {
+  worker_pool_->Shutdown();
+}
+
+void ArcLowMemoryKillerMonitor::Run() {
+  // Keep a reference to worker_pool_ in case |this| is deleted in
+  // shutdown process while this thread returns from a blocking read.
+  scoped_refptr<SequencedWorkerPool> worker_pool(worker_pool_);

[Yusuke Sato, 2016/03/14 18:02:12]

please remove this and modify the Bind code if you agree.

[cylee1, 2016/03/15 12:49:15]

Done.

+
+  static const int kMaxBufSize = 512;
+
+  FILE* kmsg_handle = fopen("/dev/kmsg", "r");

[Yusuke Sato, 2016/03/14 18:02:12]

If you really want to go with FILE, that's fine, but I think you should still
check the current calling thread with ThreadRestrictions::AssertIOAllowed() and
handle EINTR properly. In short, instead of the raw fopen, please use OpenFile
in base/files/file_util.h at least.

[cylee1, 2016/03/15 12:49:15]

Ah sorry I'm not familiar with base/files so missed such a function. I didn't
use base::File() because I can't see how to read a line using that interface.

+  char buf[kMaxBufSize];
+  int freed_size;
+  int64_t timestamp, last_timestamp = -1;
+  const TimeDelta kMaxTimeDelta = TimeDelta::FromSeconds(
+      MAX_LOWMEMORYKILL_TIME_SECS);
+
+  int kmsg_fd = fileno(kmsg_handle);
+  int flags = fcntl(kmsg_fd, F_GETFL, 0);
+  // Consume kernel messages prior to the instantiation of this object to avoid
+  // double reporting.
+  fcntl(kmsg_fd, F_SETFL, flags | O_NONBLOCK);

[Yusuke Sato, 2016/03/14 18:02:12]

SetNonBlocking()

[cylee1, 2016/03/15 12:49:15]

Done.

+  while (fgets(buf, kMaxBufSize, kmsg_handle)) {}

[Yusuke Sato, 2016/03/14 18:02:12]

The code (setting O_NONBLOCK to the underlying fd, then entering fgets loop)
seems a bit complicated, can't we just fseek to the end of the stream? Or, can't
we do something like the following?

 ct = currnettime();
 while (fgets()) {
   timestamp = parseline();
   if (timestamp < ct)
      continue;
   ...
 }

[cylee1, 2016/03/15 12:49:15]

fseek is better, I missed it.
I can't use the time recording method as you described because when logging out
Chrome OS may starts a whole new main chrome process, so losses all states. To
remember the state the only way is writing the state to disk.

+
+  // Switch back to blocking read.
+  fcntl(kmsg_fd, F_SETFL, flags & ~O_NONBLOCK);

[Yusuke Sato, 2016/03/14 18:02:12]

same

[cylee1, 2016/03/15 12:49:15]

Done.

+
+  while (fgets(buf, kMaxBufSize, kmsg_handle)) {
+    if (worker_pool->IsShutdownInProgress()) {
+      LOG(WARNING) << "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_MEMORY_KB(
+            "ArcRuntime.LowMemoryKiller.FreedSize", freed_size);
+        UMA_HISTOGRAM_LOWMEMORYKILL_TIMES(
+            "ArcRuntime.LowMemoryKiller.TimeDelta", time_delta);
+      }
+    }
+  }
+  fclose(kmsg_handle);

[Yusuke Sato, 2016/03/14 18:02:12]

CloseFile()

[cylee1, 2016/03/15 18:26:57]

Done.

+}
+
+}  // namespace arc