AvailableMemory is't calculated automatically under kenel 3.14 so it is needed to calcuate manually

manual available memory calculation should be done if only memavail is false

Manual Available Memory calculation under kernel 3.14

accurate manaul available memory calculation

mem/mem_linux.go

@@ -4,6 +4,8 @@ package mem
 
 import (
 	"context"
+	"math"
+	"os"
 	"strconv"
 	"strings"
 
@@ -103,8 +105,9 @@ func VirtualMemoryWithContext(ctx context.Context) (*VirtualMemoryStat, error) {
 	ret.Cached += ret.SReclaimable
 
 	if !memavail {
-		ret.Available = ret.Free + ret.Buffers + ret.Cached
+		ret.Available = calcuateAvailVmem(ret)
 	}
+
 	ret.Used = ret.Total - ret.Free - ret.Buffers - ret.Cached
 	ret.UsedPercent = float64(ret.Used) / float64(ret.Total) * 100.0
 
@@ -156,3 +159,39 @@ func SwapMemoryWithContext(ctx context.Context) (*SwapMemoryStat, error) {
 	}
 	return ret, nil
 }
+
+func calcuateAvailVmem(ret *VirtualMemoryStat) uint64 {
+	var watermarkLow uint64
+	fn := common.HostProc("zoneinfo")
+	lines, _ := common.ReadLines(fn)
+	pagesize := uint64(os.Getpagesize())
+	watermarkLow = 0
+
+	for _, line := range lines {
+		fields := strings.Fields(line)
+
+		if strings.HasPrefix(fields[0], "low") {
+			lowValue, err := strconv.ParseUint(fields[1], 10, 64)
+
+			if err != nil {
+				lowValue = 0
+			}
+
+			watermarkLow += lowValue
+		}
+	}
+
+	watermarkLow *= pagesize
+
+	availMemory := ret.Free - watermarkLow
+	pageCache := ret.Active + ret.Inactive
+	pageCache -= uint64(math.Min(float64(pageCache/2), float64(watermarkLow)))
+	availMemory += pageCache
+	availMemory += ret.SReclaimable - uint64(math.Min(float64(ret.SReclaimable/2.0), float64(watermarkLow)))
+
+	if availMemory < 0 {
+		availMemory = 0
+	}
+
+	return availMemory
+}