From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Vrabel <david.vrabel@citrix.com>
Subject: Re: [PATCH] xen/balloon: export balloon hotplug page
	stats to sysfs
Date: Fri, 21 Mar 2014 13:02:26 +0000
Message-ID: <532C3862.1020109@citrix.com>
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	<20140320140120.GP16807@zion.uk.xensource.com>
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To: Wei Liu <wei.liu2@citrix.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>, xen-devel@lists.xen.org
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On 20/03/14 14:01, Wei Liu wrote:
> 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.

What tools needs the value and how will it use it to make sensible
decisions?

If there isn't an answer and it just for diagnostics/debug then debugfs
is the right place.

David