Update MemoryMonitorChromeOS

Current guidelines for defining critical memory state is swapping will
occur in that situation. Update MemoryMonitorChromeOS to align the
guidelines.

- Use |available| field of base::SystemMemoryInfoKB if the OS supports it
- Don't count SwapFree as free available memory

BUG=696844

Review-Url: https://codereview.chromium.org/2731273003
Cr-Commit-Position: refs/heads/master@{#455970}

content/browser/memory/memory_monitor_chromeos.cc

@@ -25,11 +25,9 @@ int MemoryMonitorChromeOS::GetFreeMemoryUntilCriticalMB() {
   base::SystemMemoryInfoKB mem_info = {};
   delegate_->GetSystemMemoryInfo(&mem_info);
 
-  // The available memory consists of "real" and virtual (z)ram memory.
-  // Since swappable memory uses a non pre-deterministic compression and
-  // the compression creates its own "dynamic" in the system, it gets
-  // de-emphasized by the |kSwapWeight| factor.
-  const int kSwapWeight = 4;
+  // Use available free memory provided by the OS if the OS supports it.
+  if (mem_info.available > 0)
+    return mem_info.available >> kShiftKiBtoMiB;
 
   // The kernel internally uses 50MB.
   const int kMinFileMemory = 50 * 1024;
@@ -39,9 +37,8 @@ int MemoryMonitorChromeOS::GetFreeMemoryUntilCriticalMB() {
   // unless it is dirty or it's a minimal portion which is required.
   file_memory -= mem_info.dirty + kMinFileMemory;
 
-  // Available memory is the sum of free, swap and easy reclaimable memory.
-  return (mem_info.free + mem_info.swap_free / kSwapWeight + file_memory) >>
-         kShiftKiBtoMiB;
+  // Available memory is the sum of free and easy reclaimable memory.
+  return (mem_info.free + file_memory) >> kShiftKiBtoMiB;
 }
 
 // static

content/browser/memory/memory_monitor_chromeos_unittest.cc

@@ -20,12 +20,14 @@ class TestMemoryMonitorChromeOSDelegate : public TestMemoryMonitorDelegate {
                        int swap_kb,
                        int active_kb,
                        int inactive_kb,
-                       int dirty_kb) {
+                       int dirty_kb,
+                       int available_kb) {
     mem_info_.free = free_kb;
     mem_info_.swap_free = swap_kb;
     mem_info_.active_file = active_kb;
     mem_info_.inactive_file = inactive_kb;
     mem_info_.dirty = dirty_kb;
+    mem_info_.available = available_kb;
   }
 
  private:
@@ -56,10 +58,17 @@ TEST_F(MemoryMonitorChromeOSTest, GetFreeMemoryUntilCriticalMB) {
   monitor_.reset(new MemoryMonitorChromeOS(&delegate_));
   EXPECT_EQ(0u, delegate_.calls());
 
-  delegate_.SetFreeMemoryKB(256 * kKBperMB, 128 * kKBperMB, 64 * kKBperMB,
-                            32 * kKBperMB, 16 * kKBperMB);
-  EXPECT_EQ(318, monitor_->GetFreeMemoryUntilCriticalMB());
+  // |available| is supported.
+  delegate_.SetFreeMemoryKB(1 * kKBperMB, 1 * kKBperMB, 1 * kKBperMB,
+                            1 * kKBperMB, 1 * kKBperMB, 286 * kKBperMB);
+  EXPECT_EQ(286, monitor_->GetFreeMemoryUntilCriticalMB());
   EXPECT_EQ(1U, delegate_.calls());
+
+  // |available| is not supported.
+  delegate_.SetFreeMemoryKB(256 * kKBperMB, 128 * kKBperMB, 64 * kKBperMB,
+                            32 * kKBperMB, 16 * kKBperMB, 0 * kKBperMB);
+  EXPECT_EQ(286, monitor_->GetFreeMemoryUntilCriticalMB());
+  EXPECT_EQ(2U, delegate_.calls());
 }
 
 }  // namespace content