linux-kernel - Re: [Xen-devel] [PATCH] xen/balloon: Set balloon's initial state to number of existing RAM pages

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Date:	Wed, 06 Nov 2013 20:25:04 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Bob Liu <bob.liu@...cle.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>
CC:	david.vrabel@...rix.com, xen-devel@...ts.xenproject.org,
	linux-kernel@...r.kernel.org
Subject: Re: [Xen-devel] [PATCH] xen/balloon: Set balloon's initial state to number of existing RAM pages

Bob Liu <bob.liu@...cle.com> wrote:
>
>On 11/07/2013 04:37 AM, Boris Ostrovsky wrote:
>> Currently balloon's initial value is set to max_pfn which includes
>> non-RAM ranges such as MMIO hole. As result, initial memory target
>> (specified by guest's configuration file) will appear smaller than
>> what balloon driver perceives to be the current number of available
>> pages. Thus it will balloon down "extra" pages, decreasing amount of
>> available memory for no good reason.
>> 
>
>This fix the strange behavior I mentioned yesterday, every time after
>guest started balloon driver will be triggered unreasonably.
>
>> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
>> ---
>>  drivers/xen/balloon.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
>> index b232908..1b62304 100644
>> --- a/drivers/xen/balloon.c
>> +++ b/drivers/xen/balloon.c
>> @@ -641,7 +641,7 @@ static int __init balloon_init(void)
>>  
>>  	balloon_stats.current_pages = xen_pv_domain()
>>  		? min(xen_start_info->nr_pages - xen_released_pages, max_pfn)
>> -		: max_pfn;
>> +		: get_num_physpages();
>
>By the way, should the other places using max_pfn also be changed with
>get_num_physpages()?

No. In PV that calculation is correct as it gets the amount of RAM pages - which is a exactly what you need.
>
>>  	balloon_stats.target_pages  = balloon_stats.current_pages;
>>  	balloon_stats.balloon_low   = 0;
>>  	balloon_stats.balloon_high  = 0;
>> 


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