hypervisor: don't enforce a minimum memory setting

Currently, we enforce a lower limit of 256MB for the defaultMemorySize.

In general case with QEMU, this isn't a major problem, since we'll just
eat the extra page table overhead, and only consume pages when needed.
The memcgroup in the guest should make sure it only utilizes requested
amount, not what is actually available.

However, this becomes very problematic when you use preallocated memory.
In the k8s case, the VMM will get OOM killed very quickly since the host's
memory cgroup (created by kubelet) will limit the entire sandbox to the
requests + pod overhead (on the order of 140 MB). We should allow the administrator
of kata to set a better default value, which should be much closer aligned
with what's used for PodOverhead (in the kube case).

Let's remove the artifical limit in kata, and leave it up to the end
user to pick an appropriate non-default value, if desired.

Fixes: #2987

Signed-off-by: Eric Ernst <[email protected]>

pkg/katautils/config.go

@@ -326,11 +326,11 @@ func (h hypervisor) defaultMaxVCPUs() uint32 {
 }
 
 func (h hypervisor) defaultMemSz() uint32 {
-	if h.MemorySize < vc.MinHypervisorMemory {
-		return defaultMemSize // MiB
+	if h.MemorySize > 0 {
+		return h.MemorySize
 	}
 
-	return h.MemorySize
+	return defaultMemSize
 }
 
 func (h hypervisor) defaultMemSlots() uint32 {

virtcontainers/hypervisor.go

@@ -75,9 +75,6 @@ const (
 	// Port where the agent will send the logs. Logs are sent through the vsock in cases
 	// where the hypervisor has no console.sock, i.e firecracker
 	vSockLogsPort = 1025
-
-	// MinHypervisorMemory is the minimum memory required for a VM.
-	MinHypervisorMemory = 256
 )
 
 // In some architectures the maximum number of vCPUs depends on the number of physical cores.

virtcontainers/pkg/oci/utils.go

@@ -477,11 +477,7 @@ func addHypervisorMemoryOverrides(ocispec specs.Spec, sbConfig *vc.SandboxConfig
 	if value, ok := ocispec.Annotations[vcAnnotations.DefaultMemory]; ok {
 		memorySz, err := strconv.ParseUint(value, 10, 32)
 		if err != nil {
-			return fmt.Errorf("Error encountered parsing annotation for default_memory: %v, please specify positive numeric value greater than 8", err)
-		}
-
-		if memorySz < vc.MinHypervisorMemory {
-			return fmt.Errorf("Memory specified in annotation %s is less than minimum required %d, please specify a larger value", vcAnnotations.DefaultMemory, vc.MinHypervisorMemory)
+			return fmt.Errorf("Error encountered parsing annotation for default_memory: %v", err)
 		}
 
 		sbConfig.HypervisorConfig.MemorySize = uint32(memorySz)

virtcontainers/pkg/oci/utils_test.go

@@ -844,7 +844,6 @@ func TestAddHypervisorAnnotations(t *testing.T) {
 	assert.Error(err)
 
 	ocispec.Annotations[vcAnnotations.DefaultMaxVCPUs] = "1"
-	ocispec.Annotations[vcAnnotations.DefaultMemory] = fmt.Sprintf("%d", vc.MinHypervisorMemory+1)
 	assert.Error(err)
 }