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

[David Vrabel <david.vrabel@citrix.com>]

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