Merge pull request #2359 from teawater/swap_doc

Add doc for guest swap

docs/how-to/README.md

@@ -34,3 +34,4 @@
 - [How to set sandbox Kata Containers configurations with pod annotations](how-to-set-sandbox-config-kata.md)
 - [How to monitor Kata Containers in K8s](how-to-set-prometheus-in-k8s.md)
 - [How to use hotplug memory on arm64 in Kata Containers](how-to-hotplug-memory-arm64.md)
+- [How to setup swap devices in guest kernel](how-to-setup-swap-devices-in-guest-kernel.md)

docs/how-to/how-to-set-sandbox-config-kata.md

@@ -91,6 +91,13 @@ There are several kinds of Kata configurations and they are listed below.
 | `io.katacontainers.config.hypervisor.virtio_fs_cache` | string | the cache mode for virtio-fs, valid values are `always`, `auto` and `none` |
 | `io.katacontainers.config.hypervisor.virtio_fs_daemon` | string | virtio-fs `vhost-user` daemon path |
 | `io.katacontainers.config.hypervisor.virtio_fs_extra_args` | string | extra options passed to `virtiofs` daemon |
+| `io.katacontainers.config.hypervisor.enable_guest_swap` | `boolean` | enable swap in the guest |
+
+## Container Options
+| Key | Value Type | Comments |
+|-------| ----- | ----- |
+| `io.katacontainers.container.resource.swappiness"` | `uint64` | specify the `Resources.Memory.Swappiness` |
+| `io.katacontainers.container.resource.swap_in_bytes"` | `uint64` | specify the `Resources.Memory.Swap` |
 
 # CRI-O Configuration
 
@@ -100,11 +107,12 @@ In case of CRI-O, all annotations specified in the pod spec are passed down to K
 
 For containerd, annotations specified in the pod spec are passed down to Kata
 starting with version `1.3.0` of containerd. Additionally, extra configuration is
-needed for containerd, by providing a `pod_annotations` field in the containerd config
+needed for containerd, by providing `pod_annotations` field and
-file.  The `pod_annotations` field is a list of annotations that can be passed down to
+`container_annotations` field in the containerd config
-Kata as OCI annotations. It supports golang match patterns. Since annotations supported
+file.  The `pod_annotations` field and `container_annotations` field are two lists of
-by Kata follow the pattern `io.katacontainers.*`, the following configuration would work
+annotations that can be passed down to Kata as OCI annotations. They support golang match
-for passing annotations to Kata from containerd:
+patterns. Since annotations supported by Kata follow the pattern `io.katacontainers.*`,
+the following configuration would work for passing annotations to Kata from containerd:
 
 ```
 $ cat /etc/containerd/config
@@ -113,6 +121,7 @@ $ cat /etc/containerd/config
          [plugins."io.containerd.grpc.v1.cri".containerd.runtimes.kata]
            runtime_type = "io.containerd.kata.v2"
            pod_annotations = ["io.katacontainers.*"]
+           container_annotations = ["io.katacontainers.*"]
 ....
 
 ```

docs/how-to/how-to-setup-swap-devices-in-guest-kernel.md

@@ -0,0 +1,59 @@
+# Setup swap device in guest kernel
+
+## Introduction
+
+Setup swap device in guest kernel can help to increase memory capacity, handle some memory issues and increase file access speed sometimes.
+Kata Containers can insert a raw file to the guest as the swap device.
+
+## Requisites
+
+The swap config of the containers should be set by [annotations](how-to-set-sandbox-config-kata.md#container-options).  So [extra configuration is needed for containerd](how-to-set-sandbox-config-kata.md#containerd-configuration).
+
+Kata Containers just supports setup swap device in guest kernel with QEMU.
+Install and setup Kata Containers as shown [here](../install/README.md).
+
+Enable setup swap device in guest kernel as follows:
+```
+$ sudo sed -i -e 's/^#enable_guest_swap.*$/enable_guest_swap = true/g' /etc/kata-containers/configuration.toml
+```
+
+## Run a Kata Container utilizing swap device
+
+Use following command to start a Kata Container with swappiness 60 and 1GB swap device (swap_in_bytes - memory_limit_in_bytes).
+```
+$ pod_yaml=pod.yaml
+$ container_yaml=container.yaml
+$ image="quay.io/prometheus/busybox:latest"
+$ cat << EOF > "${pod_yaml}"
+metadata:
+  name: busybox-sandbox1
+EOF
+$ cat << EOF > "${container_yaml}"
+metadata:
+  name: busybox-test-swap
+annotations:
+  io.katacontainers.container.resource.swappiness: "60"
+  io.katacontainers.container.resource.swap_in_bytes: "2147483648"
+linux:
+  resources:
+    memory_limit_in_bytes: 1073741824
+image:
+  image: "$image"
+command:
+- top
+EOF
+$ sudo crictl pull $image
+$ podid=$(sudo crictl runp $pod_yaml)
+$ cid=$(sudo crictl create $podid $container_yaml $pod_yaml)
+$ sudo crictl start $cid
+```
+
+Kata Container setups swap device for this container only when `io.katacontainers.container.resource.swappiness` is set.
+
+The following table shows the swap size how to decide if `io.katacontainers.container.resource.swappiness` is set.
+|`io.katacontainers.container.resource.swap_in_bytes`|`memory_limit_in_bytes`|swap size|
+|---|---|---|
+|set|set| `io.katacontainers.container.resource.swap_in_bytes` - `memory_limit_in_bytes`|
+|not set|set| `memory_limit_in_bytes`|
+|not set|not set| `io.katacontainers.config.hypervisor.default_memory`|
+|set|not set|cgroup doesn't support this usage|