Memory plugin: use 'available' instead of 'actual_'

Closes #214

plugins/system/MEM_README.md

@@ -7,17 +7,18 @@ explanation of the difference between `used` and `actual_used` RAM, see
 [Linux ate my ram](http://www.linuxatemyram.com/).
 
 - **total**: total physical memory available
-- **actual_free**: the actual amount of available memory that can be given instantly
-to processes that request more memory in bytes; this is calculated by summing
-different memory values depending on the platform (e.g. free + buffers + cached on Linux)
-and it is supposed to be used to monitor actual memory usage in a cross platform fashion.
-- **actual_used**: inverse of actual_free, see above
-- **actual_used_percent**: the percentage usage calculated as (total - actual_used) / total * 100
+- **available**: the actual amount of available memory that can be given instantly
+to processes that request more memory in bytes; In linux kernel 3.14+, this
+is available natively in /proc/meminfo. In other platforms, this is calculated by
+summing different memory values depending on the platform
+(e.g. free + buffers + cached on Linux).
+It is supposed to be used to monitor actual memory usage in a cross platform fashion.
+- **available_percent**: Percent of memory available, `available / total * 100`
 - **used**: memory used, calculated differently depending on the platform and
 designed for informational purposes only.
 - **free**: memory not being used at all (zeroed) that is readily available; note
 that this doesn't reflect the actual memory available (use 'available' instead).
-- **used_percent**: the percentage usage calculated as (total - used) / total * 100
+- **used_percent**: the percentage usage calculated as `(total - used) / total * 100`
 
 ## Measurements:
 #### Raw Memory measurements:
@@ -28,8 +29,7 @@ Meta:
 
 Measurement names:
 - mem_total
-- mem_actual_free
-- mem_actual_used
+- mem_available
 - mem_used
 - mem_free
 
@@ -41,4 +41,4 @@ Meta:
 
 Measurement names:
 - mem_used_percent
-- mem_actual_used_percent
+- mem_available_percent

plugins/system/memory.go

@@ -25,13 +25,12 @@ func (s *MemStats) Gather(acc plugins.Accumulator) error {
 	vmtags := map[string]string(nil)
 
 	acc.Add("total", vm.Total, vmtags)
-	acc.Add("actual_free", vm.Available, vmtags)
-	acc.Add("actual_used", vm.Total-vm.Available, vmtags)
+	acc.Add("available", vm.Available, vmtags)
 	acc.Add("used", vm.Used, vmtags)
 	acc.Add("free", vm.Free, vmtags)
 	acc.Add("used_percent", 100*float64(vm.Used)/float64(vm.Total), vmtags)
-	acc.Add("actual_used_percent",
-		100*float64(vm.Total-vm.Available)/float64(vm.Total),
+	acc.Add("available_percent",
+		100*float64(vm.Available)/float64(vm.Total),
 		vmtags)
 
 	return nil

plugins/system/system_test.go

@@ -230,11 +230,10 @@ func TestSystemStats_GenerateStats(t *testing.T) {
 	vmtags := map[string]string(nil)
 
 	assert.True(t, acc.CheckTaggedValue("total", uint64(12400), vmtags))
-	assert.True(t, acc.CheckTaggedValue("actual_free", uint64(7600), vmtags))
-	assert.True(t, acc.CheckTaggedValue("actual_used", uint64(12400-7600), vmtags))
+	assert.True(t, acc.CheckTaggedValue("available", uint64(7600), vmtags))
 	assert.True(t, acc.CheckTaggedValue("used", uint64(5000), vmtags))
-	assert.True(t, acc.CheckTaggedValue("actual_used_percent",
-		float64(12400-7600)/float64(12400)*100,
+	assert.True(t, acc.CheckTaggedValue("available_percent",
+		float64(7600)/float64(12400)*100,
 		vmtags))
 	assert.True(t, acc.CheckTaggedValue("used_percent",
 		float64(5000)/float64(12400)*100,