Contents

Introduction

Prerequisites

Requirements

What are HugePages?

Problem Description

Analysis

Troubleshoot

Introduction

This document describes the procedure to analyze the issue related to high memory usage in Cisco Virtualized Infrastructure Manager (CVIM) compute nodes.

Prerequisites

Requirements

Cisco recommends you have knowledge of memory management and HugePages in Linux.

What are HugePages?

Enabling HugePages allows the operating system to support memory pages larger than the default (usually 4 KB). The use of very large page sizes can enhance system performance by reducing the system resources needed to access page table entries. Consequently, HugePages are typically employed to mitigate memory latency.

Problem Description

High memory usage alerts on CVIM compute nodes while CVIM has not triggered any alerts. Alerts related to memory utilization could be via a third-party monitoring tool or monitoring dashboard.

Analysis

It is observed that high memory utilization in the OS as per the free and  sar command output in Linux.

[root@cvim-computex ~]# free -m

total    used    free   shared  buff/cache  available

Mem:           385410  365882   7602     3621       11925        8411

Swap:            2047       0   2047

[root@cvim-computex ~]# sar -r

Linux 4.18.0-193.81.1.el8_2.x86_64 (pod1-compute4.mx2) 08/24/2023 _x86_64_ (112 CPU)

12:00:46 AM kbmemfree kbavail kbmemused %memused kbbuffers kbcached kbcommit %commit kbactive kbinact kbdirty

12:10:34 AM   7493576 7871200 387166528    98.10      4240  9334356 12893752    3.25  4891940 6325076      68

12:20:11 AM   7503208 7883396 387156896    98.10      4240  9337364 12872708    3.24  4885008 6328096      16

12:30:34 AM   7485648 7869540 387174456    98.10      4240  9340556 12902748    3.25  4892948 6331276      36

12:40:46 AM   7494396 7880940 387165708    98.10      4240  9343636 12866964    3.24  4886908 6334364      20

12:50:34 AM   7479616 7869772 387180488    98.10      4240  9346720 12905156    3.25  4892408 6337444      56

01:00:46 AM   7490304 7883016 387169800    98.10      4240  9349832 12860152    3.24  4885308 6340500      56

01:10:34 AM   7472248 7868672 387187856    98.11      4240  9352836 12896932    3.25  4892604 6343556      28

01:20:46 AM   7484308 7883276 387175796    98.10      4240  9355948 12867972    3.24  4885172 6346676      16

01:30:34 AM   7475092 7869596 387185012    98.11      4240  9350840 12904328    3.25  4892448 6341556      44

01:40:46 AM   7485436 7882508 387174668    98.10      4240  9353932 12864252    3.24  4885148 6344660      56

01:50:34 AM   7468840 7869520 387191264    98.11      4240  9357036 12907464    3.25  4893552 6347752     164

02:00:46 AM   7479076 7882428 387181028    98.10      4240  9360124 12861892    3.24  4886044 6350844      68

Use the  ps  command to identify the processes with the highest memory usage.

[root@cvim-computex ~]# ps -aux --sort -rss

USER         PID %CPU %MEM VSZ       RSS TTY STAT  START TIME COMMAND

root      328199 1207  0.2 541893584 ?   RLl Mar12 2948779:31 /usr/bin/vpp -c /etc/vpp/vpp.conf

root        1829  0.0  0.0 379024  227692 ?  Ss    Mar12 14:21 /usr/lib/systemd/systemd-journald

Verify the container memory usage by checking the statistics using the  podman  or  docker  commands.

[root@cvim-computex ~]# podman stats

ID            NAME                 CPU % MEM USAGE / LIMIT MEM % NET IO  BLOCK IO          PIDS

2f8fdc4b63a4 fluentd_31902         --    301.2MB / 404.1GB 0.07% -- / -- 9.265MB / 89.68GB 75

34d806a30733 novalibvirt_31902     --    42.16MB / 404.1GB 0.01% -- / -- 589.8kB / 22.13MB 44

48292d2fa956 novassh_31902         --    5.882MB / 404.1GB 0.00% -- / -- 475.1kB / 167.3MB 2

7b2ce84e86b3 novacompute_31902     --    231.8MB / 404.1GB 0.06% -- / -- 761.9kB / 2.43GB  49

89c01c14ef3f neutron_vpp_31902     --    1.209GB / 404.1GB 0.30% -- / -- 0B / 7.66MB       35

Based on the provided output, it appears that no processes are exhibiting high memory usage. Additionally, the containers seem to be utilizing a low amount of memory.

The  free  command still shows high memory usage.

root@cvim-computex ~]# free -m

total     used   free   shared    buff/cache available

Mem:        385410   366751  7310    3496          11348   7696

Swap:         2047        5  2042

[root@cvim-computex ~]#

Troubleshoot

To comprehend this memory utilization, knowledge of HugePage memory is essential.

If the pod is enabled with HugePages, care must be taken to use the right flavor, to ensure that the system memory is not used to launch the VMs. The usage of system memory for VMs can lead to CVIM instability, as both the workload and the infrastructure are competing for the resources reserved for the infrastructure.

Check the HugePages:

[root@cvim-computex ~]# tail /sys/devices/system/node/node0/hugepages/hugepages-2048kB/nr_hugepages

90001

[root@cvim-computex ~]# tail /sys/devices/system/node/node0/hugepages/hugepages-1048576kB/nr_hugepages

0

[root@cvim-computex ~]# tail /sys/devices/system/node/node1/hugepages/hugepages-2048kB/nr_hugepages

90000

[root@cvim-computex ~]# tail /sys/devices/system/node/node1/hugepages/hugepages-1048576kB/nr_hugepages

0

[root@cvim-computex ~]#

nr_hugepages  is the total number of HugePages.

(90001 + 90000) x 2M = 360GB is reserved for HugePage.

Also, note that 5% memory of total physical memory is reserved for normal memory pages (4KB) for OS usage even if 100% HugePage is configured.

385GB (free total) - 360GB (reserved for HugePage) = 25GB is reserved for Normal Pages.

So, high memory utilization, as observed in the  sar   and  free commands is expected.

Use the mentioned command to check the actual memory usage.

[root@mgmt-node ~]# ip -br -4 a s br_api

br_api UP 10.x.x.x/24

[root@mgmt-node ~]# curl -sS -g -u admin:password --cacert /var/www/mercury/mercury-ca.crt https://10.x.x.x:9090/api/v1/query --data-urlencode 'query=100 * (mem_free + mem_buffered + mem_cached) / ((mem_total - sum without(NUMAnode, pagename, pagesize) (hugepages_nr)) or mem_total)' | python -mjson.tool

sample output:

{

"status": "success",

"data": {

"resultType": "vector",

"result": [

{

"metric": {

"host": "cvim-computex",

"instance": "10.x.x.x:9273",

"job": "telegraf",

"node_type": "compute"

},

"value": [

1693479719.383,

"76.16486394450624" --> Actual available memory percentage.

]

},

{

"metric": {

"host": "cvim-computey",

"instance": "10.x.x.x:9273",

"job": "telegraf",

"node_type": "compute"

},

"value": [

1693479719.383,

"76.63431887455388"

CVIM triggers an alert only when the available memory is less than 10%.

Alert Name - mem_available_percent

There is less than 10% of available system memory. Regular 4K pages memory is used by both the system and OpenStack infrastructure services and does not include huge pages. This alert can indicate either an insufficient amount of RAM or abnormal memory usage by the system or infrastructure.