Fixed bug where server complains about "Insufficient free RAM to start VM"...

Fixed bug where server complains about "Insufficient free RAM to start VM" despite enough RAM available

src/consts/consts.go

@@ -11,4 +11,12 @@ const (
 	VMSpiceMaxPort = 65000
 
 	MaxUploadSize = "30G"
+
+	// We estimate that KVM allows for this amount of RAM saving in %
+	// (due to page sharing across VMs).
+	KsmRamSaving = 0.3
+
+	// To prevent RAM saturation, we refuse running new VMs if more than
+	// this amount of memory is being used (in %).
+	RamUsageLimit = .85
 )

src/qga/qga.go

@@ -38,6 +38,7 @@ func (q *QGACon)SendShutdown() error {
 	return err
 }
 
+// TODO: work in progress...
 func (q *QGACon)WriteFile(filePath string) error {
 	filePath = "/home/nexus/pipo.txt"
 	_, err := q.sock.Write([]byte(`{"execute":"guest-file-open", "arguments":{"path":"`+filePath+`","mode":"w+"}}`))

src/utils/memory.go

@@ -23,7 +23,6 @@ func GetRAM() (int, int, error) {
 
 	var memTotal int = -1
 	var memAvail int = -1
-
 	const units = 1024
 
     for scan.Scan() {

src/vms/vms.go

@@ -4,6 +4,7 @@ import (
 	"os"
 	"sort"
 	"sync"
+	"math"
 	"errors"
 	"path/filepath"
 	"nexus-server/exec"
@@ -23,6 +24,7 @@ type (
 		dir string             // Base directory where VMs are stored
 		rwlock *sync.RWMutex   // RWlock to ensure the coherency of the map (m) of VMs
 		usedPorts [65536]bool  // Indicates which ports are used by the VMs
+		usedRAM int            // Used RAM by running VMs (in MB)
 	}
 )
 
@@ -39,7 +41,7 @@ func GetVMsInstance() *VMs {
 // NOTE: path is the root directory where VMs reside.
 func InitVMs() error {
 	vmsDir := paths.GetInstance().VMsDir
-	vms = &VMs { m: make(map[string]VM), dir: vmsDir, rwlock: new(sync.RWMutex) }
+	vms = &VMs { m: make(map[string]VM), dir: vmsDir, rwlock: new(sync.RWMutex), usedRAM: 0 }
 
 	errMsg := "Failed reading VMs directory: "
 	dirs1, err := utils.GetSubDirs(vmsDir)
@@ -170,18 +172,20 @@ func (vms *VMs)StartVM(vmID uuid.UUID) (int, string, error) {
 		return 0, "", err
 	}
 
-	_, availRAM, err := utils.GetRAM()
+	totalRAM, availRAM, err := utils.GetRAM()
 	if err != nil {
 		return -1, "", errors.New("Failed obtaining memory info: "+err.Error())
 	}
 
-	// Check there will be at least 16GB of RAM left after the VM has started,
-	// otherwise, we prevent the execution of the VM to avoid RAM saturation.
-	// Thanks to Linux's KSVM technology, pages sharing the same content are actually shared
-	// which dramatically reduces the amount of RAM being used (roughly ~50% in average).
-	log.Info("vm.RAM: ", vm.Ram)
-	log.Info("Available RAM: ", availRAM)
-	if availRAM - vm.Ram < 16*1024  {
+	// We estimate that KVM allows for ~30% RAM saving (due to page sharing across VMs).
+	estimatedVmRAM := int(math.Round(float64(vm.Ram)*(1.-consts.KsmRamSaving)))
+
+	vms.usedRAM += estimatedVmRAM
+
+	// Checks that at least 15% of the available RAM is left after the VM has started,
+	// otherwise, refuses to run it in order to avoid RAM saturation.
+	if availRAM - vms.usedRAM <= int(math.Round(float64(totalRAM)*(1.-consts.RamUsageLimit))) {
+		vms.usedRAM -= estimatedVmRAM
 		return -1, "", errors.New("Insufficient free RAM to start VM")
 	}
 
@@ -205,6 +209,7 @@ func (vms *VMs)StartVM(vmID uuid.UUID) (int, string, error) {
 		vm.mutex.Unlock()
 		vms.rwlock.Lock()
 		vms.usedPorts[vm.Run.Port] = false
+		vms.usedRAM -= estimatedVmRAM
 		vms.updateVMMap(vm)
 		vms.rwlock.Unlock()
 	}
@@ -213,6 +218,7 @@ func (vms *VMs)StartVM(vmID uuid.UUID) (int, string, error) {
 	pwd, err := vm.start(port, endofExecFn)
 	vms.updateVMMap(&vm)
 	vm.mutex.Unlock()
+
 	return port, pwd, err
 }