Document the changes of scheduler PostFilter extension point

content/en/docs/concepts/configuration/pod-priority-preemption.md

@@ -65,24 +65,20 @@ PriorityClasses have the option to set `preemptionPolicy: Never`.
 This will prevent pods of that PriorityClass from preempting other pods.
 {{< /note >}}
 
-Preemption is controlled by a kube-scheduler flag `disablePreemption`, which is
-set to `false` by default.
-If you want to disable preemption despite the above note, you can set
-`disablePreemption` to `true`.
-
-This option is available in component configs only and is not available in
-old-style command line options. Below is a sample component config to disable
-preemption:
+Starting from Kubernetes 1.19, Preemption is controlled by a kube-scheduler
+plugin: `DefaultPreemption`, which is enabled by default.
+If you want to disable preemption despite the above note, below is a sample
+component config:
 
 ```yaml
-apiVersion: kubescheduler.config.k8s.io/v1alpha1
+apiVersion: kubescheduler.config.k8s.io/v1beta1
 kind: KubeSchedulerConfiguration
-algorithmSource:
-  provider: DefaultProvider
-
-...
-
-disablePreemption: true
+profiles:
+  - schedulerName: default-scheduler
+    plugins:
+      postFilter:
+        disabled:
+        - name: DefaultPreemption
 ```
 
 ## PriorityClass

content/en/docs/concepts/scheduling-eviction/scheduling-framework.md

@@ -75,6 +75,14 @@ node, the scheduler will call filter plugins in their configured order. If any
 filter plugin marks the node as infeasible, the remaining plugins will not be
 called for that node. Nodes may be evaluated concurrently.
 
+### PostFilter {#post-filter}
+
+These plugins are called after Filter phase, but only when there is no feasible
+node. Each plugin is called by their configured order. If any postFilter plugin
+marks the node as `Schedulable`, the remaining plugins will not be called.
+A typical PostFilter implementation is preemption, which tries to make the pod
+schedulable by preempting other Pods.
+
 ### PreScore {#pre-score}
 
 These plugins are used to perform "pre-scoring" work, which generates a sharable