WIP: memory coordinator: Check /dev/chromeos-low-mem to determine memory condition

base/memory/memory_pressure_monitor_chromeos.cc

Index: base/memory/memory_pressure_monitor_chromeos.cc
diff --git a/base/memory/memory_pressure_monitor_chromeos.cc b/base/memory/memory_pressure_monitor_chromeos.cc
index 05fcc9e1511acf80fbcc4611309ca214473e120c..120cd6be1c8d3f02c59cd700901fe7a528d00388 100644
--- a/base/memory/memory_pressure_monitor_chromeos.cc
+++ b/base/memory/memory_pressure_monitor_chromeos.cc
@@ -4,14 +4,10 @@
 
 #include "base/memory/memory_pressure_monitor_chromeos.h"
 
-#include <fcntl.h>
-#include <sys/select.h>
-
+#include "base/memory/ptr_util.h"
 #include "base/metrics/histogram_macros.h"
-#include "base/posix/eintr_wrapper.h"
 #include "base/process/process_metrics.h"
 #include "base/single_thread_task_runner.h"
-#include "base/sys_info.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "base/time/time.h"
 
@@ -47,11 +43,6 @@ enum MemoryPressureLevelUMA {
   NUM_MEMORY_PRESSURE_LEVELS
 };
 
-// This is the file that will exist if low memory notification is available
-// on the device.  Whenever it becomes readable, it signals a low memory
-// condition.
-const char kLowMemFile[] = "/dev/chromeos-low-mem";
-
 // Converts a |MemoryPressureThreshold| value into a used memory percentage for
 // the moderate pressure event.
 int GetModerateMemoryThresholdInPercent(
@@ -86,21 +77,6 @@ MemoryPressureListener::MemoryPressureLevel GetMemoryPressureLevelFromFillLevel(
              : MemoryPressureListener::MEMORY_PRESSURE_LEVEL_CRITICAL;
 }
 
-// This function will be called less than once a second. It will check if
-// the kernel has detected a low memory situation.
-bool IsLowMemoryCondition(int file_descriptor) {
-  fd_set fds;
-  struct timeval tv;
-
-  FD_ZERO(&fds);
-  FD_SET(file_descriptor, &fds);
-
-  tv.tv_sec = 0;
-  tv.tv_usec = 0;
-
-  return HANDLE_EINTR(select(file_descriptor + 1, &fds, NULL, NULL, &tv)) > 0;
-}
-
 }  // namespace
 
 MemoryPressureMonitor::MemoryPressureMonitor(
@@ -113,14 +89,11 @@ MemoryPressureMonitor::MemoryPressureMonitor(
           GetModerateMemoryThresholdInPercent(thresholds)),
       critical_pressure_threshold_percent_(
           GetCriticalMemoryThresholdInPercent(thresholds)),
-      low_mem_file_(HANDLE_EINTR(::open(kLowMemFile, O_RDONLY))),
+      low_mem_observer_(base::MakeUnique<LowMemoryObserver>()),
       dispatch_callback_(
           base::Bind(&MemoryPressureListener::NotifyMemoryPressure)),
       weak_ptr_factory_(this) {
   StartObserving();
-  LOG_IF(ERROR,
-         base::SysInfo::IsRunningOnChromeOS() && !low_mem_file_.is_valid())
-      << "Cannot open kernel listener";
 }
 
 MemoryPressureMonitor::~MemoryPressureMonitor() {
@@ -194,7 +167,7 @@ void MemoryPressureMonitor::CheckMemoryPressure() {
   // computation come to similar results and then remove this override again.
   // TODO(skuhne): Add some testing framework here to see how close the kernel
   // and the internal functions are.
-  if (low_mem_file_.is_valid() && IsLowMemoryCondition(low_mem_file_.get())) {
+  if (low_mem_observer_->IsLowMemoryCondition()) {
     current_memory_pressure_level_ =
         MemoryPressureListener::MEMORY_PRESSURE_LEVEL_CRITICAL;
   } else {
@@ -205,9 +178,9 @@ void MemoryPressureMonitor::CheckMemoryPressure() {
 
     // When listening to the kernel, we ignore the reported memory pressure
     // level from our own computation and reduce critical to moderate.
-    if (low_mem_file_.is_valid() &&
+    if (low_mem_observer_->is_valid() &&
         current_memory_pressure_level_ ==
-        MemoryPressureListener::MEMORY_PRESSURE_LEVEL_CRITICAL) {
+            MemoryPressureListener::MEMORY_PRESSURE_LEVEL_CRITICAL) {
       current_memory_pressure_level_ =
           MemoryPressureListener::MEMORY_PRESSURE_LEVEL_MODERATE;
     }