Merge pull request #24140 from qiutongs/master

Add a new known issue to the out-of-resource doc: active_file memory is not considered as available memory

Author: k8s-ci-robot

content/en/docs/tasks/administer-cluster/out-of-resource.md

@@ -341,4 +341,11 @@ to prevent system OOMs, and promote eviction of workloads so cluster state can r
 The Pod eviction may evict more Pods than needed due to stats collection timing gap. This can be mitigated by adding
 the ability to get root container stats on an on-demand basis [(https://github.com/google/cadvisor/issues/1247)](https://github.com/google/cadvisor/issues/1247) in the future.
 
+### active_file memory is not considered as available memory
+
+On Linux, the kernel tracks the number of bytes of file-backed memory on active LRU list as the `active_file` statistic. The kubelet treats `active_file` memory areas as not reclaimable. For workloads that make intensive use of block-backed local storage, including ephemeral local storage, kernel-level caches of file and block data means that many recently accessed cache pages are likely to be counted as `active_file`. If enough of these kernel block buffers are on the active LRU list, the kubelet is liable to observe this as high resource use and taint the node as experiencing memory pressure - triggering Pod eviction.
+
+For more more details, see [https://github.com/kubernetes/kubernetes/issues/43916](https://github.com/kubernetes/kubernetes/issues/43916)
+
+You can work around that behavior by setting the memory limit and memory request the same for containers likely to perform intensive I/O activity. You will need to estimate or measure an optimal memory limit value for that container.