Resizing /dev/shm

Scenario

/dev/shm consists of a temporary file system (tmpfs). tmpfs is a memory-based file system implemented in Linux/Unix and has high read/write efficiency.

In CCI 2.0, the default size of /dev/shm is 64 MB, which cannot meet customer requirements. You can change its size for data exchange between processes or temporary data storage.

This topic shows how to resize /dev/shm by setting memory-backed emptyDir or configuring securityContext and mount commands.

Constraints

/dev/shm uses a memory-based tmpfs to temporarily store data. Data is not retained after the container is restarted.
You can use either of the following methods to change the size of /dev/shm. However, do not use both methods in one pod.
The emptyDir uses the memory requested by the pod and does not occupy extra resources.
Writing data in /dev/shm is equivalent to requesting memory. In this scenario, you need to evaluate the memory usage of processes. When the sum of the memory requested by processes in the container and the data volume in the emptyDir exceeds the memory limit of the container, memory overflow occurs.
When resizing /dev/shm, set the size to 50% of the pod's memory request.

Resizing /dev/shm Using Memory-backed emptyDir

emptyDir is applicable to temporary data storage, disaster recovery, and runtime data sharing. It will be deleted upon deletion or transfer of workload pods.

CCI 2.0 allows you to mount memory-backed emptyDir. You can specify the memory size allocated to the emptyDir and mount it to the /dev/shm directory in the container to resize /dev/shm.

apiVersion: cci/v2
kind: Pod
metadata:  
 name: pod-emptydir-name
spec:  
 containers:   
  - image: 'library/ubuntu:latest'     
    volumeMounts:      
     - name: volume-emptydir1    
       mountPath: /dev/shm   
    name: container-0   
    resources:      
     limits:        
      cpu: '4'      
      memory: 8Gi  
     requests:   
      cpu: '4'    
      memory: 8Gi 
 volumes:   
  - emptyDir:     
     medium: Memory   
     sizeLimit: 4Gi  
    name: volume-emptydir1

After the pod is started, run the df -h command to go to the /dev/shm directory. If the following information is displayed, the size is successfully modified.

Figure 1 /dev/shm directory details