Adding proper GetUsedMemoryInPercent calculation

athena/resource_manager/delegate/resource_manager_delegate.cc

Index: athena/resource_manager/delegate/resource_manager_delegate.cc
diff --git a/athena/resource_manager/delegate/resource_manager_delegate.cc b/athena/resource_manager/delegate/resource_manager_delegate.cc
index ca76c650907b1cf80d434601a9c31717bdf46479..f0ea87646a0ab4db96b107e7387f793b2f01af40 100644
--- a/athena/resource_manager/delegate/resource_manager_delegate.cc
+++ b/athena/resource_manager/delegate/resource_manager_delegate.cc
@@ -25,11 +25,37 @@ class ResourceManagerDelegateImpl : public ResourceManagerDelegate {
 
  private:
   virtual int GetUsedMemoryInPercent() OVERRIDE {
-    base::SystemMemoryInfoKB memory;
-    // TODO(skuhne): According to semenzato this calculation has to change.
-    if (base::GetSystemMemoryInfo(&memory) &&
-        memory.total > 0 && memory.free >= 0) {
-      return ((memory.total - memory.free) * 100) / memory.total;
+    base::SystemMemoryInfoKB info;
+    if (base::GetSystemMemoryInfo(&info)) {

[Jun Mukai, 2014/08/29 22:59:32]

Early exit like if(!base::GetSystemMemoryInfo(&info)) { LOG(WARNING) << ...;
return 0; }
would be better.

[Mr4D (OOO till 08-26), 2014/08/29 23:44:03]

Done.

+      // TODO(skuhne): Instead of adding the kernel memory pressure calculation
+      // logic here, we should have a kernel mechanism similar to the low memory
+      // notifier in ChromeOS which offers multiple pressure states.
+      // To track this, we have crbug.com/381196.
+
+      // 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;
+
+      // The total memory we have is the "real memory" plus the virtual (z)ram.
+      int total_memory = info.total + info.swap_total / kSwapWeight;
+
+      // The kernel internally uses 50MB.
+      int min_file_memory = 50 * 1024;

[Jun Mukai, 2014/08/29 22:59:32]

const int kMinFileMemory = ...

[Mr4D (OOO till 08-26), 2014/08/29 23:44:03]

Done.

+
+      // Most file memory can be easily reclaimed.
+      int file_memory = info.active_file + info.inactive_file;
+      // unless it is dirty or it's a minimal portion which is required.
+      file_memory -= info.dirty - min_file_memory;

[Jun Mukai, 2014/08/29 22:59:33]

If dirty is less than 50MB, it will increase file_memory, right?
should be std::max(0, info.dirty - ...)?

[Mr4D (OOO till 08-26), 2014/08/29 23:44:03]

sign got now corrected.

+
+      // Available memory is the sum of free, swap and easy reclaimable memory.
+      int available_memory =
+          info.free + info.swap_free / kSwapWeight + file_memory;

[Jun Mukai, 2014/08/29 22:59:33]

or this could be std::min(file_memory, min_file_memory) here rather than
operating above?

[Mr4D (OOO till 08-26), 2014/08/29 23:44:03]

According to our semenzato that isn't a problem. (I had it that way before). But
the worst which can happen is that the fill goes above 100% - which is treated
as above 90% anyways.

+
+      DCHECK(available_memory < total_memory);
+      int percentage = ((total_memory - available_memory) * 100) / total_memory;
+      return percentage;
     }
     LOG(WARNING) << "Cannot determine the free memory of the system.";
     return 0;