feat(scheduler): adding SpaceWeighted scheduler (#178)

adding a new scheduler logic which selects the node
which has max free space available. This is better scheduling
algorithm than the volumeweighted and capacity weighted where we
don't check for the free space available on the node.

Signed-off-by: Pawan <[email protected]>

Author: pawanpraka1

deploy/lvm-operator.yaml

@@ -1160,7 +1160,9 @@ metadata:
 value: 900000000
 globalDefault: false
 description: "This priority class should be used for the OpenEBS LVM localPV CSI driver controller deployment only."
+
 ---
+
 kind: StatefulSet
 apiVersion: apps/v1
 metadata:

pkg/driver/schd_helper.go

@@ -17,11 +17,13 @@ limitations under the License.
 package driver
 
 import (
+	"math"
 	"regexp"
 	"strconv"
 
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 
+	"github.com/openebs/lvm-localpv/pkg/builder/nodebuilder"
 	"github.com/openebs/lvm-localpv/pkg/builder/volbuilder"
 	"github.com/openebs/lvm-localpv/pkg/lvm"
 )
@@ -32,8 +34,11 @@ const (
 	VolumeWeighted = "VolumeWeighted"
 
 	// pick the node where total provisioned volumes have occupied less capacity from the given volume group
-	// this will be the default scheduler when none provided
 	CapacityWeighted = "CapacityWeighted"
+
+	// pick the node which is less loaded space wise
+	// this will be the default scheduler when none provided
+	SpaceWeightedMap = "SpaceWeighted"
 )
 
 // getVolumeWeightedMap goes through all the volumegroup on all the nodes
@@ -92,14 +97,50 @@ func getCapacityWeightedMap(re *regexp.Regexp) (map[string]int64, error) {
 	return nmap, nil
 }
 
+// getSpaceWeightedMap returns how weighted a node is space wise.
+// The node which has max free space available is less loaded and
+// can accumulate more volumes.
+func getSpaceWeightedMap(re *regexp.Regexp) (map[string]int64, error) {
+	nmap := map[string]int64{}
+
+	nodeList, err := nodebuilder.NewKubeclient().
+		WithNamespace(lvm.LvmNamespace).
+		List(metav1.ListOptions{})
+
+	if err != nil {
+		return nmap, err
+	}
+
+	for _, node := range nodeList.Items {
+		var maxFree int64 = 0
+		for _, vg := range node.VolumeGroups {
+			if re.MatchString(vg.Name) {
+				freeCapacity := vg.Free.Value()
+				if maxFree < freeCapacity {
+					maxFree = freeCapacity
+				}
+			}
+		}
+		if maxFree > 0 {
+			// converting to SpaceWeighted by subtracting it with MaxInt64
+			// as the node which has max free space available is less loaded.
+			nmap[node.Name] = math.MaxInt64 - maxFree
+		}
+	}
+
+	return nmap, nil
+}
+
 // getNodeMap returns the node mapping for the given scheduling algorithm
 func getNodeMap(schd string, vgPattern *regexp.Regexp) (map[string]int64, error) {
 	switch schd {
 	case VolumeWeighted:
 		return getVolumeWeightedMap(vgPattern)
 	case CapacityWeighted:
 		return getCapacityWeightedMap(vgPattern)
+	case SpaceWeightedMap:
+		return getSpaceWeightedMap(vgPattern)
 	}
-	// return CapacityWeighted(default) if not specified
-	return getCapacityWeightedMap(vgPattern)
+	// return getSpaceWeightedMap(default) if not specified
+	return getSpaceWeightedMap(vgPattern)
 }