[lxc-users] LXD 2.14 - Ubuntu 16.04 - kernel 4.4.0-57-generic - SWAP continuing to grow

[Ron Kelley]

Wondering if anyone else has similar issues.

We have 5x LXD 2.12 servers running (U16.04 - kernel 4.4.0-57-generic - 8G RAM, 19G SWAP).  Each server is running about 50 LXD containers - Wordpress w/Nginx and PHP7.  The servers have been running for about 15 days now, and swap space continues to grow.  In addition, the kswapd0 process starts consuming CPU until we flush the system cache via "/bin/echo 3 > /proc/sys/vm/drop_caches” command.

Our LXD profile looks like this:
-------------------------
config:
  limits.cpu: "2"
  limits.memory: 512MB
  limits.memory.swap: "true"
  limits.memory.swap.priority: "1"
-------------------------


We also have added these to /etc/sysctl.conf
-------------------------
vm.swappiness=10
vm.vfs_cache_pressure=50
-------------------------

A quick “top” output shows plenty of available Memory and buff/cache.  But, for some reason, the system continues to swap out the app.  For example, our “server-4” machine shows 8G total RAM, 500MB free, 2.5G available, and 5G of buff/cache.  Yet, swap is at 5.5GB and has been slowly growing over the past few days.  It seems something is preventing the apps from using the RAM.


To be honest, we have been battling lots of memory/swap issues using LXD.  We started with no tuning, but the app stack quickly ran out of memory.  After editing the profile to allow 512MB RAM per container (and restarting the container), the kswapd0 issue happens.  Given all the issues we have had with memory and swap using LXD, we are seriously considering moving back to the traditional VM approach until LXC/LXD is better “baked”.


-Ron