Editing VSwap

New [[Download/kernel/rhel6|RHEL6-based OpenVZ]] kernel has a new memory management model, which supersedes [[UBC|User beancounters]]. It is called '''VSwap'''.

Now you can set two primary parameters: <code>physpages</code> and <code>swappages</code>, while all the other beancounters become secondary.

* '''physpages'''
: This parameter limits the physical memory (RAM) available to processes inside a container.
: The <code>barrier</code> is ignored, and the <code>limit</code> sets the limit.
: Currently the user memory and the page cache are accounted into <code>physpages</code>.

* '''swappages'''
: This parameter limits the amount of swap space which can be used for processes inside a container.
: The <code>barrier</code> is ignored, and the <code>limit</code> sets the limit.

The sum of <code>physpages.limit</code> and <code>swappages.limit</code> 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.

=== Secondary parameters ===
'''Even though these settings are classed as secondary, they are still important settings!'''

In addition to <code>physpages</code> and <code>swappages</code> being set, it is ''currently'' recommended to:

* Set <code>kmemsize</code> to no more than 1/2 of <code>physpages</code>
* Set <code>dcachesize</code> to no more than 1/2 of <code>kmemsize</code>
* Set <code>lockedpages</code> to no more than 1/2 of <code>physpages</code>

VSwap CT config samples (like [http://git.openvz.org/?p=vzctl;a=blob;f=etc/conf/ve-vswap-256m.conf-sample ve-vswap-256m.conf-sample] that come with vzctl are currently implementing these recommendations.

{{Note|VSwap feature is still being worked on, so these recommendation might change in the future.}}

{{Note|As of 042stab042 and later kernels, you are not required to set kmemsize, dcachesize and lockedpages resources, so you can set those to unlimited.  For more information, see Kir's blog post on the subject [http://openvz.livejournal.com/39765.html].}}

[[Category: UBC]]