Re: [PATCH] xen/balloon: export balloon hotplug page stats to sysfs

[Wei Liu <wei.liu2@citrix.com>]

On Thu, Mar 20, 2014 at 01:21:17PM +0000, David Vrabel wrote:
> On 20/03/14 12:56, Wei Liu wrote:
> > --- a/drivers/xen/xen-balloon.c
> > +++ b/drivers/xen/xen-balloon.c
> > @@ -129,6 +129,11 @@ module_exit(balloon_exit);
> >  BALLOON_SHOW(current_kb, "%lu\n", PAGES2KB(balloon_stats.current_pages));
> >  BALLOON_SHOW(low_kb, "%lu\n", PAGES2KB(balloon_stats.balloon_low));
> >  BALLOON_SHOW(high_kb, "%lu\n", PAGES2KB(balloon_stats.balloon_high));
> > +#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
> > +BALLOON_SHOW(hotplug_kb, "%lu\n", PAGES2KB(balloon_stats.hotplug_pages));
> > +BALLOON_SHOW(balloon_hotplug_kb, "%lu\n",
> > +	     PAGES2KB(balloon_stats.balloon_hotplug));
> > +#endif
> 
> Extending the kernel's ABI requires justification.  How are these values
> useful for userspace tools?  If it's just for debug purposes, using
> debugfs would be preferred.
> 

My original thought is that userspace tools have the right to know how
many pages balloon driver has. Missing the hotplug pages is not very
desirable. But I have yet known any tools that require balloon hotplug
page stat -- after all they probably don't know there's such a thing is
nothing is exported. Also note that these BALLOON_SHOW fields are
read-only, so exporting more stats won't in any way affect system
behavior.

If you prefer debugfs I can switch to use that.

Wei.

> David