runtime: clh: Add reclaim_guest_freed_memory [BACKPORT]

We're bringing to *Cloud Hypervisor only* the reclaim_guest_freed_memory
option already present in the runtime-rs.

This allows us to use virtio-balloon for the hypervisor to reclaim
memory freed by the guest.

The reason we're not touching other hypervisors is because we're very
much aware of avoiding to clutter the go code at this point, so we'll
leave it for whoever really needs this on other hypervisor (and trust
me, we really do need it for Cloud Hypervisor right now ;-)).

Signed-off-by: Champ-Goblem <cameron@northflank.com>
Signed-off-by: Fabiano Fidêncio <fidencio@northflank.com>

src/runtime/config/configuration-clh.toml.in

@@ -185,6 +185,16 @@ block_device_driver = "virtio-blk"
 # Default false
 #block_device_cache_direct = true
 
+# Reclaim guest freed memory.
+# Enabling this will result in the VM balloon device having f_reporting=on set.
+# Then the hypervisor will use it to reclaim guest freed memory.
+# This is useful for reducing the amount of memory used by a VM.
+# Enabling this feature may sometimes reduce the speed of memory access in
+# the VM.
+#
+# Default false
+#reclaim_guest_freed_memory = true
+
 # Enable huge pages for VM RAM, default false
 # Enabling this will result in the VM memory
 # being allocated using huge pages.

src/runtime/pkg/katautils/config-settings.go.in

@@ -76,6 +76,7 @@ const defaultBlockDeviceCacheDirect bool = false
 const defaultBlockDeviceCacheNoflush bool = false
 const defaultEnableIOThreads bool = false
 const defaultEnableMemPrealloc bool = false
+const defaultEnableReclaimGuestFreedMemory bool = false
 const defaultEnableHugePages bool = false
 const defaultEnableIOMMU bool = false
 const defaultEnableIOMMUPlatform bool = false

src/runtime/pkg/katautils/config.go

@@ -147,6 +147,7 @@ type hypervisor struct {
 	VhostUserDeviceReconnect       uint32                    `toml:"vhost_user_reconnect_timeout_sec"`
 	DisableBlockDeviceUse          bool                      `toml:"disable_block_device_use"`
 	MemPrealloc                    bool                      `toml:"enable_mem_prealloc"`
+	ReclaimGuestFreedMemory        bool                      `toml:"reclaim_guest_freed_memory"`
 	HugePages                      bool                      `toml:"enable_hugepages"`
 	VirtioMem                      bool                      `toml:"enable_virtio_mem"`
 	IOMMU                          bool                      `toml:"enable_iommu"`
@@ -1082,6 +1083,7 @@ func newClhHypervisorConfig(h hypervisor) (vc.HypervisorConfig, error) {
 		VirtioFSCacheSize:              h.VirtioFSCacheSize,
 		VirtioFSCache:                  h.VirtioFSCache,
 		MemPrealloc:                    h.MemPrealloc,
+		ReclaimGuestFreedMemory:        h.ReclaimGuestFreedMemory,
 		HugePages:                      h.HugePages,
 		FileBackedMemRootDir:           h.FileBackedMemRootDir,
 		FileBackedMemRootList:          h.FileBackedMemRootList,
@@ -1434,6 +1436,7 @@ func GetDefaultHypervisorConfig() vc.HypervisorConfig {
 		DisableBlockDeviceUse:    defaultDisableBlockDeviceUse,
 		DefaultBridges:           defaultBridgesCount,
 		MemPrealloc:              defaultEnableMemPrealloc,
+		ReclaimGuestFreedMemory:  defaultEnableReclaimGuestFreedMemory,
 		HugePages:                defaultEnableHugePages,
 		IOMMU:                    defaultEnableIOMMU,
 		IOMMUPlatform:            defaultEnableIOMMUPlatform,

src/runtime/pkg/oci/utils.go

@@ -705,6 +705,12 @@ func addHypervisorMemoryOverrides(ocispec specs.Spec, sbConfig *vc.SandboxConfig
 		sbConfig.HypervisorConfig.FileBackedMemRootDir = value
 	}
 
+	if err := newAnnotationConfiguration(ocispec, vcAnnotations.ReclaimGuestFreedMemory).setBool(func(reclaimGuestFreedMemory bool) {
+		sbConfig.HypervisorConfig.ReclaimGuestFreedMemory = reclaimGuestFreedMemory
+	}); err != nil {
+		return err
+	}
+
 	if err := newAnnotationConfiguration(ocispec, vcAnnotations.HugePages).setBool(func(hugePages bool) {
 		sbConfig.HypervisorConfig.HugePages = hugePages
 	}); err != nil {

src/runtime/virtcontainers/clh.go

@@ -527,7 +527,15 @@ func (clh *cloudHypervisor) CreateVM(ctx context.Context, id string, network Net
 		hotplugSize := clh.config.DefaultMaxMemorySize
 		// OpenAPI only supports int64 values
 		clh.vmconfig.Memory.HotplugSize = func(i int64) *int64 { return &i }(int64((utils.MemUnit(hotplugSize) * utils.MiB).ToBytes()))
+
+		if clh.config.ReclaimGuestFreedMemory {
+			// Create VM with a balloon config so we can enable free page reporting (size of the balloon can be set to zero)
+			clh.vmconfig.Balloon = chclient.NewBalloonConfig(0)
+			// Set the free page reporting flag for ballooning to be true
+			clh.vmconfig.Balloon.SetFreePageReporting(true)
+		}
 	}
+
 	// Set initial amount of cpu's for the virtual machine
 	clh.vmconfig.Cpus = chclient.NewCpusConfig(int32(clh.config.NumVCPUs()), int32(clh.config.DefaultMaxVCPUs))
 

src/runtime/virtcontainers/hypervisor.go

@@ -612,6 +612,9 @@ type HypervisorConfig struct {
 	// MemPrealloc specifies if the memory should be pre-allocated
 	MemPrealloc bool
 
+	// ReclaimGuestFreedMemory is a sandbox annotation that specifies whether the memory freed by the guest will be reclaimed by the hypervisor or not.
+	ReclaimGuestFreedMemory bool
+
 	// HugePages specifies if the memory should be pre-allocated from huge pages
 	HugePages bool
 

src/runtime/virtcontainers/pkg/annotations/annotations.go

@@ -167,6 +167,9 @@ const (
 	// MemPrealloc is a sandbox annotation that specifies the memory space used for nvdimm device by the hypervisor.
 	MemPrealloc = kataAnnotHypervisorPrefix + "enable_mem_prealloc"
 
+	// ReclaimGuestFreedMemory is a sandbox annotation that specifies whether the memory freed by the guest will be reclaimed by the hypervisor or not.
+	ReclaimGuestFreedMemory = kataAnnotHypervisorPrefix + "reclaim_guest_freed_memory"
+
 	// HugePages is a sandbox annotation to specify if the memory should be pre-allocated from huge pages
 	HugePages = kataAnnotHypervisorPrefix + "enable_hugepages"