Add Slab, Shared and PageTables metric for VirtualMemory under linux

mem/mem.go

@@ -54,6 +54,9 @@ type VirtualMemoryStat struct {
 	Writeback    uint64 `json:"writeback"`
 	Dirty        uint64 `json:"dirty"`
 	WritebackTmp uint64 `json:"writebacktmp"`
+	Shared       uint64 `json:"shared"`
+	Slab         uint64 `json:"slab"`
+	PageTables   uint64 `json:"pagetables"`
 }
 
 type SwapMemoryStat struct {

mem/mem_linux.go

@@ -52,6 +52,12 @@ func VirtualMemory() (*VirtualMemoryStat, error) {
 			ret.WritebackTmp = t * 1024
 		case "Dirty":
 			ret.Dirty = t * 1024
+		case "Shmem":
+			ret.Shared = t * 1024
+		case "Slab":
+			ret.Slab = t * 1024
+		case "PageTables":
+			ret.PageTables = t * 1024
 		}
 	}
 	if !memavail {

mem/mem_test.go

@@ -52,7 +52,7 @@ func TestVirtualMemoryStat_String(t *testing.T) {
 		UsedPercent: 30.1,
 		Free:        40,
 	}
-	e := `{"total":10,"available":20,"used":30,"usedPercent":30.1,"free":40,"active":0,"inactive":0,"wired":0,"buffers":0,"cached":0,"writeback":0,"dirty":0,"writebacktmp":0}`
+	e := `{"total":10,"available":20,"used":30,"usedPercent":30.1,"free":40,"active":0,"inactive":0,"wired":0,"buffers":0,"cached":0,"writeback":0,"dirty":0,"writebacktmp":0,"shared":0,"slab":0,"pagetables":0}`
 	if e != fmt.Sprintf("%v", v) {
 		t.Errorf("VirtualMemoryStat string is invalid: %v", v)
 	}