Manual 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
+}