Container is unreachable under certain type of load

Applies to:

• Virtuozzo 7.5.X

Symptoms

A container may seem to be frozen, or operating extremely slow if:

• UBC resource dcachesize is high
• there is no free memory left
• kmemsize and sum of RSS is close to container's memory limit
• there are services/processes accessing many different files (e.g. php-fpmservice)

Resolution

Under such memory pressure, kernel tries to precisely count size of all kernel memory related to that container, which can take significant time on servers with lots of containers.

To avoid performance issues for such containers, change global configuration option:

    ~# sysctl -w vm.vfs_cache_min_ratio=0 ## defaults to 2

To apply on the server's start, save this value to /etc/sysctl.conf.