Merge pull request #24504 from hqhq/soften_update_kmem

Soften limitation of update kernel memory

daemon/update.go

@@ -61,10 +61,6 @@ func (daemon *Daemon) update(name string, hostConfig *container.HostConfig) erro
 		return errCannotUpdate(container.ID, fmt.Errorf("Container is marked for removal and cannot be \"update\"."))
 	}
 
-	if container.IsRunning() && hostConfig.KernelMemory != 0 {
-		return errCannotUpdate(container.ID, fmt.Errorf("Can not update kernel memory to a running container, please stop it first."))
-	}
-
 	if err := container.UpdateContainer(hostConfig); err != nil {
 		restoreConfig = true
 		return errCannotUpdate(container.ID, err)

docs/reference/commandline/update.md

@@ -38,9 +38,23 @@ space-separated list of container names or IDs.
 
 With the exception of the `--kernel-memory` value, you can specify these
 options on a running or a stopped container. You can only update
-`--kernel-memory` on a stopped container. When you run `docker update` on
-stopped container, the next time you restart it, the container uses those
-values.
+`--kernel-memory` on a stopped container or on a running container with
+kernel memory initialized. For example, if you started a container with
+command:
+
+    # docker run -ti --name test --kernel-memory 50M ubuntu bash
+
+You can update kernel memory of this running container:
+
+    # docker update --kernel-memory 80M test
+
+If you started a container without kernel memory initialized:
+
+    # docker run -ti --name test2 --memory 300M ubuntu bash
+
+Update kernel memory of running container `test2` will fail, you can only
+stop the container and update kernel memory then. The next time you
+restart it, the container uses the new value.
 
 Another configuration you can change with this command is restart policy,
 new restart policy will take effect instantly after you run `docker update`

integration-cli/docker_cli_update_unix_test.go

@@ -120,17 +120,27 @@ func (s *DockerSuite) TestUpdateKernelMemory(c *check.C) {
 
 	name := "test-update-container"
 	dockerCmd(c, "run", "-d", "--name", name, "--kernel-memory", "50M", "busybox", "top")
+	dockerCmd(c, "update", "--kernel-memory", "100M", name)
+
+	c.Assert(inspectField(c, name, "HostConfig.KernelMemory"), checker.Equals, "104857600")
+
+	file := "/sys/fs/cgroup/memory/memory.kmem.limit_in_bytes"
+	out, _ := dockerCmd(c, "exec", name, "cat", file)
+	c.Assert(strings.TrimSpace(out), checker.Equals, "104857600")
+}
+
+func (s *DockerSuite) TestUpdateKernelMemoryUninitialized(c *check.C) {
+	testRequires(c, DaemonIsLinux, kernelMemorySupport)
+
+	name := "test-update-container"
+	dockerCmd(c, "run", "-d", "--name", name, "busybox", "top")
 	_, _, err := dockerCmdWithError("update", "--kernel-memory", "100M", name)
-	// Update kernel memory to a running container is not allowed.
+	// Update kernel memory to a running container without kernel memory initialized is not allowed.
 	c.Assert(err, check.NotNil)
 
-	// Update kernel memory to a running container with failure should not change HostConfig
-	c.Assert(inspectField(c, name, "HostConfig.KernelMemory"), checker.Equals, "52428800")
-
 	dockerCmd(c, "pause", name)
 	_, _, err = dockerCmdWithError("update", "--kernel-memory", "100M", name)
 	c.Assert(err, check.NotNil)
-	c.Assert(inspectField(c, name, "HostConfig.KernelMemory"), checker.Equals, "52428800")
 	dockerCmd(c, "unpause", name)
 
 	dockerCmd(c, "stop", name)

man/docker-update.1.md

@@ -30,9 +30,23 @@ provide space-separated list of container names or IDs.
 
 With the exception of the `--kernel-memory` value, you can specify these
 options on a running or a stopped container. You can only update
-`--kernel-memory` on a stopped container. When you run `docker update` on
-stopped container, the next time you restart it, the container uses those
-values.
+`--kernel-memory` on a stopped container or on a running container with
+kernel memory initialized. For example, if you started a container with
+command:
+
+    # docker run -ti --name test --kernel-memory 50M ubuntu bash
+
+You can update kernel memory of this running container:
+
+    # docker update --kernel-memory 80M test
+
+If you started a container without kernel memory initialized:
+
+    # docker run -ti --name test2 --memory 300M ubuntu bash
+
+Update kernel memory of running container `test2` will fail, you can only
+stop the container and update kernel memory then. The next time you
+restart it, the container uses the new value.
 
 Another configuration you can change with this command is restart policy,
 new restart policy will take effect instantly after you run `docker update`
@@ -63,8 +77,9 @@ on a container.
 **--kernel-memory**=""
    Kernel memory limit (format: `<number>[<unit>]`, where unit = b, k, m or g)
 
-   Note that you can not update kernel memory to a running container, it can only
-be updated to a stopped container, and affect after it's started.
+   Note that you can not update kernel memory to a running container if the container
+is started without kernel memory initialized, in this case, it can only be updated
+after it's stopped, and affect after it's started.
 
 **-m**, **--memory**=""
    Memory limit (format: <number><optional unit>, where unit = b, k, m or g)