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It can be accessed and reviewed at: https://github.com/lxc/lxd/pull/7955
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=== Description (from pull-request) ===
Adds support for shrinking the memory limit of VM (when hugepages are not being used) using `lxc config set limits.memory`.
From ae4618cf9461a9e1def2fdf9196cc55f8cb3e841 Mon Sep 17 00:00:00 2001
From: Thomas Parrott <thomas.parr...@canonical.com>
Date: Wed, 30 Sep 2020 10:28:29 +0100
Subject: [PATCH 1/2] lxd/instance/drivers/qmp/monitor: Adds
GetBalloonSizeBytes and SetBalloonSizeBytes
Signed-off-by: Thomas Parrott <thomas.parr...@canonical.com>
---
lxd/instance/drivers/qmp/monitor.go | 38 +++++++++++++++++++++++++++++
1 file changed, 38 insertions(+)
diff --git a/lxd/instance/drivers/qmp/monitor.go
b/lxd/instance/drivers/qmp/monitor.go
index fb4bacf2eb..11c011da38 100644
--- a/lxd/instance/drivers/qmp/monitor.go
+++ b/lxd/instance/drivers/qmp/monitor.go
@@ -322,3 +322,41 @@ func (m *Monitor) GetCPUs() ([]int, error) {
return pids, nil
}
+
+// GetBalloonSizeBytes returns the current size of the memory balloon in bytes.
+func (m *Monitor) GetBalloonSizeBytes() (int64, error) {
+ respRaw, err := m.qmp.Run([]byte("{'execute': 'query-balloon'}"))
+ if err != nil {
+ m.Disconnect()
+ return -1, ErrMonitorDisconnect
+ }
+
+ // Process the response.
+ var respDecoded struct {
+ Return struct {
+ Actual int64 `json:"actual"`
+ } `json:"return"`
+ }
+
+ err = json.Unmarshal(respRaw, &respDecoded)
+ if err != nil {
+ return -1, ErrMonitorBadReturn
+ }
+
+ return respDecoded.Return.Actual, nil
+}
+
+// SetBalloonSizeBytes sets the size of the memory balloon in bytes.
+func (m *Monitor) SetBalloonSizeBytes(sizeBytes int64) error {
+ respRaw, err := m.qmp.Run([]byte(fmt.Sprintf("{'execute': 'balloon',
'arguments': {'value': %d}}", sizeBytes)))
+ if err != nil {
+ m.Disconnect()
+ return ErrMonitorDisconnect
+ }
+
+ if string(respRaw) != `{"return": {}}` {
+ return ErrMonitorBadReturn
+ }
+
+ return nil
+}
From 1023637b7bab9ac02540100ecb633bbbb12a4087 Mon Sep 17 00:00:00 2001
From: Thomas Parrott <thomas.parr...@canonical.com>
Date: Wed, 30 Sep 2020 10:29:02 +0100
Subject: [PATCH 2/2] lxd/instance/drivers/driver/qemu: Adds live shrinking of
memory
Signed-off-by: Thomas Parrott <thomas.parr...@canonical.com>
---
lxd/instance/drivers/driver_qemu.go | 82 +++++++++++++++++++++++++++--
1 file changed, 79 insertions(+), 3 deletions(-)
diff --git a/lxd/instance/drivers/driver_qemu.go
b/lxd/instance/drivers/driver_qemu.go
index 8572365fb2..c1cf5c91f2 100644
--- a/lxd/instance/drivers/driver_qemu.go
+++ b/lxd/instance/drivers/driver_qemu.go
@@ -2659,7 +2659,9 @@ func (vm *qemu) Rename(newName string) error {
// Update the instance config.
func (vm *qemu) Update(args db.InstanceArgs, userRequested bool) error {
- // Only user.* keys can be changed on a running VM
+ // Only certain can be changed on a running VM.
+ liveUpdateKeys := []string{"limits.memory"}
+
if vm.IsRunning() {
if args.Config == nil {
args.Config = map[string]string{}
@@ -2720,8 +2722,8 @@ func (vm *qemu) Update(args db.InstanceArgs,
userRequested bool) error {
}
for _, key := range changedConfig {
- if !strings.HasPrefix(key, "user.") {
- return fmt.Errorf("Only user.* keys can be
updated on running VMs")
+ if !strings.HasPrefix(key, "user.") &&
!shared.StringInSlice(key, liveUpdateKeys) {
+ return fmt.Errorf("Key %q cannot be updated
when VM is running", key)
}
}
@@ -2733,6 +2735,19 @@ func (vm *qemu) Update(args db.InstanceArgs,
userRequested bool) error {
}
}
+ for _, key := range changedConfig {
+ value := vm.expandedConfig[key]
+
+ if key == "limits.memory" {
+ err = vm.updateMemoryLimit(value)
+ if err != nil {
+ if err != nil {
+ return errors.Wrapf(err,
"Failed updating memory limit")
+ }
+ }
+ }
+ }
+
err = vm.state.Cluster.Transaction(func(tx *db.ClusterTx) error
{
object, err := tx.GetInstance(vm.project, vm.name)
if err != nil {
@@ -3070,6 +3085,67 @@ func (vm *qemu) Update(args db.InstanceArgs,
userRequested bool) error {
return nil
}
+// updateMemoryLimit live updates the VM's memory limit by shrinking the
balloon device.
+// Only memory shrinking is supported at this time.
+func (vm *qemu) updateMemoryLimit(newLimit string) error {
+ if shared.IsTrue(vm.expandedConfig["limits.memory.hugepages"]) {
+ return fmt.Errorf("Cannot live update memory limit when using
huge pages")
+ }
+
+ // Check new size string is valid and convert to bytes.
+ newSizeBytes, err := units.ParseByteSizeString(newLimit)
+ if err != nil {
+ return errors.Wrapf(err, "Invalid memory size")
+ }
+
+ // Connect to the monitor.
+ monitor, err := qmp.Connect(vm.monitorPath(), qemuSerialChardevName,
vm.getMonitorEventHandler())
+ if err != nil {
+ return err // The VM isn't running as no monitor socket
available.
+ }
+
+ curSizeBytes, err := monitor.GetBalloonSizeBytes()
+ if err != nil {
+ return err
+ }
+
+ if curSizeBytes == newSizeBytes {
+ return nil
+ } else if curSizeBytes < newSizeBytes {
+ return fmt.Errorf("Cannot increase memory size when VM is
running")
+ }
+
+ // Shrink balloon device.
+ err = monitor.SetBalloonSizeBytes(newSizeBytes)
+ if err != nil {
+ return err
+ }
+
+ // Shrinking the balloon can take time, so poll the actual balloon size
to check it has shrunk within 1%
+ // of the target size, which we then take as success (it may still
continue to shrink closer to target).
+ for i := 0; i < 5; i++ {
+ curSizeBytes, err = monitor.GetBalloonSizeBytes()
+ if err != nil {
+ return err
+ }
+
+ var diff int64
+ if curSizeBytes < newSizeBytes {
+ diff = newSizeBytes - curSizeBytes
+ } else {
+ diff = curSizeBytes - newSizeBytes
+ }
+
+ if diff <= (newSizeBytes / 100) {
+ return nil // We reached to within 1% of our target
size.
+ }
+
+ time.Sleep(500 * time.Millisecond)
+ }
+
+ return fmt.Errorf("Failed setting memory to %d bytes (currently %d
bytes) as it was taking too long", newSizeBytes, curSizeBytes)
+}
+
func (vm *qemu) updateDevices(removeDevices deviceConfig.Devices, addDevices
deviceConfig.Devices, updateDevices deviceConfig.Devices, oldExpandedDevices
deviceConfig.Devices) error {
isRunning := vm.IsRunning()
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