Difference between revisions of "VSwap"
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If you have an existing container with usual UBC parameters set, and you want to convert this one into VSwap enabled config, here's what you need to do. | If you have an existing container with usual UBC parameters set, and you want to convert this one into VSwap enabled config, here's what you need to do. | ||
| − | # Decide on how much RAM and swap you want this CT to have. | + | # Decide on how much RAM and swap you want this CT to have. Generally, sum of your new RAM+swap should be more or less equal to sum of old PRIVVMPAGES and KMEMSIZE. |
# Manually remove all UBC parameters from config. '''This is optional''', you can still have UBC limits applied if you want. | # Manually remove all UBC parameters from config. '''This is optional''', you can still have UBC limits applied if you want. | ||
| − | + | # Add PHYSPAGES and SWAPPAGES parameters to config. Easiest way is to use <code>vzctl set $CTID --ram N --swap M --save</code> | |
Now your config is vswap enabled, and when you (re)start it, vswap mechanism will be used by the kernel for this CT. | Now your config is vswap enabled, and when you (re)start it, vswap mechanism will be used by the kernel for this CT. | ||
Revision as of 16:41, 17 January 2012
New RHEL6-based OpenVZ kernel has a new memory management model, which supersedes User beancounters. It is called VSwap.
Now you can set two primary parameters: physpages and swappages, while all the other beancounters become secondary and optional.
- physpages
- This parameter limits the physical memory (RAM) available to processes inside a container.
- The
barrieris ignored and should be set to 0, and thelimitsets the limit. - Currently (as of >= 042stab042) the user memory, the kernel memory and the page cache are accounted into
physpages.
- swappages
- This parameter limits the amount of swap space which can be used for processes inside a container.
- The
barrieris ignored and should be set to 0, and thelimitsets the limit.
The sum of physpages.limit and swappages.limit limits the maximum amount
of allocated memory which can be used by a container. When physpages limit
is reached, memory pages belonging to the container are pushed out to
so called virtual swap (vswap). The difference between normal swap
and vswap is that with vswap no actual disk I/O usually occurs. Instead,
a container is artificially slowed down, to emulate the effect of the real
swapping. Actual swap out occurs only if there is a global memory shortage
on the system.
Setting
Since vzctl 3.0.30, you can use --ram and --swap parameters, like this:
vzctl set 777 --ram 512M --swap 1G --save
If you are converting an existing CT from old (non-vswap) configuration, you can either
- leave all the other UBC parameters as-is,
- or set those to 'unlimited',
- or remove those from configuration file.
Convert non-vswap CT to Vswap
If you have an existing container with usual UBC parameters set, and you want to convert this one into VSwap enabled config, here's what you need to do.
- Decide on how much RAM and swap you want this CT to have. Generally, sum of your new RAM+swap should be more or less equal to sum of old PRIVVMPAGES and KMEMSIZE.
- Manually remove all UBC parameters from config. This is optional, you can still have UBC limits applied if you want.
- Add PHYSPAGES and SWAPPAGES parameters to config. Easiest way is to use
vzctl set $CTID --ram N --swap M --save
Now your config is vswap enabled, and when you (re)start it, vswap mechanism will be used by the kernel for this CT.
