Re: [libvirt][PATCH v4 0/3] introduce 'restrictive' mode in numatune

On Wed, Mar 24, 2021 at 09:46:23PM +0100, Martin Kletzander wrote: > On Tue, Mar 23, 2021 at 09:48:02AM +0000, Daniel P. Berrangé wrote: > > On Tue, Mar 23, 2021 at 10:59:02AM +0800, Luyao Zhong wrote: > > > Before this patch set, numatune only has three memory modes: > > > static, interleave and prefered. These memory policies are > > > ultimately set by mbind() system call. > > > > > > Memory policy could be 'hard coded' into the kernel, but none of > > > above policies fit our requirment under this case. mbind() support > > > default memory policy, but it requires a NULL nodemask. So obviously > > > setting allowed memory nodes is cgroups' mission under this case. > > > So we introduce a new option for mode in numatune named 'restrictive'. > > > > > > <numatune> > > > <memory mode="restrictive" nodeset="1-4,^3"/> > > > <memnode cellid="0" mode="restrictive" nodeset="1"/> > > > <memnode cellid="2" mode="restrictive" nodeset="2"/> > > > </numatune> > > > > 'restrictive' is rather a wierd name and doesn't really tell me what > > the memory policy is going to be. As far as I can tell from the > > patches, it seems this causes us to not set any memory alllocation > > policy at all. IOW, we're using some undefined host default policy. > > > > Given this I think we should be calling it either "none" or "default" > > > > I was against "default" because having such option possible, but the actual > default being different sounds stupid. Similarly "none" sounds like no > restrictions are applied or that it is the same as if nothing was specified. It > is funny to imagine the situation when I am explaining to someone how to achieve > this solution: > > "The default is 'strict', you need to explicitly set it to 'default'." These patches aren't claiming the default is strict though - they're saying the default is whatever the kernel has been configured to be. The kernel could apply interleave, or preferred or strict. So using "default" as the term is fine, because we explicitly aren't guaranteing which behaviour is used.

Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|