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..30f80a816bfea9bf8ba8ea9ba2110b67ac7c9c96 100644
--- a/athena/resource_manager/delegate/resource_manager_delegate.cc
+++ b/athena/resource_manager/delegate/resource_manager_delegate.cc
@@ -4,6 +4,7 @@
 
 #include "athena/resource_manager/public/resource_manager_delegate.h"
 
+#include <algorithm>
 #include <string>
 
 #include "base/logging.h"
@@ -25,11 +26,35 @@ 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) && info.total > 0 && info.free >= 0) {

[Luigi Semenzato, 2014/08/29 15:37:36]

Not sure that you should check info.total and info.free.  If GetSystemMemoryInfo
returns true, info.total should have a sane value, and if not, it's not your job
to report problems here i.e. the sanity check should already happen inside
GetSystemMemoryInfo.  Same for info.free.

[Mr4D (OOO till 08-26), 2014/08/29 16:45:47]

Done.

+      // TODO(skuhne): Instead of adding the kernel memory pressure calculation

[Luigi Semenzato, 2014/08/29 15:37:36]

Do you want to open a bug to keep track of this?

[Mr4D (OOO till 08-26), 2014/08/29 16:45:47]

Done.

+      // logic here, we should have a kernel mechanism similar to the low memory
+      // notifier in ChromeOS which offers multiple pressure states.
+
+      // The available memory consists of "real" and virtual (z)ram memory.
+      // Since swapp-able memory uses a non pre-deterministic compression and

[Luigi Semenzato, 2014/08/29 15:37:36]

"swappable" may be better

[Mr4D (OOO till 08-26), 2014/08/29 16:45:46]

Done.

+      // the compression creates it's own "dynamic" in the system, it gets

[Luigi Semenzato, 2014/08/29 15:37:36]

its

[Mr4D (OOO till 08-26), 2014/08/29 16:45:46]

Done.

+      // 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;
+
+      // We don't know this value - it's kernel internal.

[Luigi Semenzato, 2014/08/29 15:37:36]

Just use 50Mb.  You're already copying kernel internals by making the same
calculation as the kernel.

[Mr4D (OOO till 08-26), 2014/08/29 16:45:46]

Done.

+      int min_file_memory = 0;
+
+      // 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;
+
+      // Available memory is the sum of free, swap and easy reclaimable memory.
+      int available_memory =
+          info.free + info.swap_free / kSwapWeight + file_memory;
+
+      int percentage = ((total_memory - available_memory) * 100) / total_memory;
+      return std::min(0, std::max(percentage, 100));

[Luigi Semenzato, 2014/08/29 15:37:36]

available memory can be assumed to be positive, so you only have to check that
available_memory < total_memory, and log an error if it is not.

[Mr4D (OOO till 08-26), 2014/08/29 16:45:47]

Done. I might be wrong, but what if the compression ratio comes out to be much
higher then expected. Wouldn't it be possible to have then more avail then total
memory?

[Luigi Semenzato, 2014/08/29 18:42:56]

Ah, good question.  This may be a concern in general but not with our typical
numbers: our swap is at most 1.5 * RAM size, and divided by 4 it's 0.375 * RAM
so...

but OK, you can leave as is.  Either way.


On 2014/08/29 16:45:47, Mr4D wrote:

     }
     LOG(WARNING) << "Cannot determine the free memory of the system.";
     return 0;