[virt-tools-list] [virt-manager gui feature request] check box for "locked" memory backing

[Cole Robinson]

On 09/19/2018 05:57 AM, Joachim Wagner wrote:
> While various cli options for memory backing have been introduced in 2014, the
> virt-manager GUI doesn't offer any memory options other than current and
> maximum allocation under open -> view -> details -> memory. The "locked"
> memory backing option is probably the most easy to to understand and can have
> huge impact when the host also acts as a file server or runs write-intense
> applications. It would be useful to many users to have a check box for it in
> the GUI.
> 
> Indications for a need for this check box:
>   * https://serverfault.com/questions/561446/how-can-i-keep-important-vms-in-memory-without-disabling-swap/
>   * https://serverfault.com/questions/477886/why-does-host-swap-out-vms-when-there-are-16gb-of-buffer-cache-and-swappiness
> 
> The other options may also be useful but typical users will require much more
> guidance than offered in the libvirt documentation. I only start understanding
> them reading <https://www.suse.com/documentation/sles-15/singlehtml/
> article_vt_best_practices/article_vt_best_practices.html>.
> 

This is one of those XML bits that's questionable to expose in the UI. 
It's very important for some users, but it's 1) difficult to explain in 
the UI, 2) has tricky operational caveats (see 
https://libvirt.org/formatdomain.html#elementsMemoryBacking), 3) has a 
limited audience who are already power users.

There's already a fairly easy command line way to enable this option, 
once you know what it is:
virt-xml $VMNAME --edit --memorybacking locked=on

As the years go on and these types of requests seem to increase in 
frequency, I'm thinking virt-manager really needs a raw XML editing 
mode. Power users can make tweaks to the XML without leaving the UI, and 
it will take a lot of pressure off us to implement/maintain/test power 
user type options. That way the UI can refocus on the 90% case. 
Hopefully I can get time to experiment with it by the end of the year

- Cole