Fix: set Swappiness when no mem limits

This hard codes -1 on inspect for Docker's API to return `null` and be compatible

Signed-off-by: Nicola Sella <nsella@redhat.com>

Author: inknos

pkg/api/handlers/compat/containers.go

@@ -526,6 +526,13 @@ func LibpodToContainerJSON(l *libpod.Container, sz bool) (*container.InspectResp
 		hc.CgroupnsMode = container.CgroupnsModeHost
 	}
 
+	swappiness := int64(-1)
+	hc.MemorySwappiness = &swappiness
+
+	// Docker reports null instead of 0 for unset Swappiness
+	if *hc.MemorySwappiness == -1 {
+		hc.MemorySwappiness = nil
+	}
 	// k8s-file == json-file
 	if hc.LogConfig.Type == define.KubernetesLogging {
 		hc.LogConfig.Type = define.JSONLogging

test/apiv2/20-containers.at

@@ -782,6 +782,16 @@ if root && test -e /dev/nullb0; then
   podman rm -f updateCtr
 fi
 
+# test MemorySwappiness
+podman run -d --rm --name swappiness_with_mem_limit --memory 200M quay.io/libpod/alpine:latest top
+podman run -d --rm --name swappiness_without_mem_limit quay.io/libpod/alpine:latest top
+
+t GET containers/swappiness_with_mem_limit/json 200 \
+  .HostConfig.MemorySwappiness=null
+t GET containers/swappiness_without_mem_limit/json 200 \
+  .HostConfig.MemorySwappiness=null
+
+podman stop -t0 swappiness_with_mem_limit swappiness_without_mem_limit
 
 # test if API support -1 for ulimits https://github.com/containers/podman/issues/24886