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

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));
> > +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

If you prefer debugfs I can switch to use that.


> David

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