From mboxrd@z Thu Jan  1 00:00:00 1970
From: Wei Liu <wei.liu2@citrix.com>
Subject: Re: [PATCH] xen/balloon: export balloon hotplug page
	stats to sysfs
Date: Thu, 20 Mar 2014 14:01:20 +0000
Message-ID: <20140320140120.GP16807@zion.uk.xensource.com>
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To: David Vrabel <david.vrabel@citrix.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>, Wei Liu <wei.liu2@citrix.com>, xen-devel@lists.xen.org
List-Id: xen-devel@lists.xenproject.org

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