Re: [PATCH 1/5] xen: use maximum reservation to limit amount of usable RAM

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

On 31/08/11 21:40, Konrad Rzeszutek Wilk wrote:
>> Signed-off-by: David Vrabel <david.vrabel@citrix.com>
>> ---
>>  arch/x86/xen/setup.c |   19 +++++++++++++++++++
>>  1 files changed, 19 insertions(+), 0 deletions(-)
>>
>> diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
>> index df118a8..c3b8d44 100644
>> --- a/arch/x86/xen/setup.c
>> +++ b/arch/x86/xen/setup.c
>> @@ -184,6 +184,19 @@ static unsigned long __init xen_set_identity(const struct e820entry *list,
>>  					PFN_UP(start_pci), PFN_DOWN(last));
>>  	return identity;
>>  }
>> +
>> +static unsigned long __init xen_get_max_pages(void)
>> +{
>> +	unsigned long max_pages = MAX_DOMAIN_PAGES;
>> +	domid_t domid = DOMID_SELF;
>> +	int ret;
>> +
>> +	ret = HYPERVISOR_memory_op(XENMEM_maximum_reservation, &domid);
>> +	if (ret > 0)
>> +		max_pages = ret;
>> +	return min(max_pages, MAX_DOMAIN_PAGES);
>> +}
>> +
>>  /**
>>   * machine_specific_memory_setup - Hook for machine specific memory setup.
>>   **/
>> @@ -292,6 +305,12 @@ char * __init xen_memory_setup(void)
>>  
>>  	sanitize_e820_map(e820.map, ARRAY_SIZE(e820.map), &e820.nr_map);
>>  
>> +	extra_limit = xen_get_max_pages();
>> +	if (extra_limit >= max_pfn)
>> +		extra_pages = extra_limit - max_pfn;
>> +	else
>> +		extra_pages = 0;
>> +
>>  	extra_pages += xen_return_unused_memory(xen_start_info->nr_pages, &e820);
> 
> I ran this on three setups:
> 
> 1) PV (domU)
> 2) PV+PCI (dom0)
> 3) PV+PCI+e820_hole=1 (domU)
> 
> and then the same without this patch.
> 
> Both the 2) and 3) worked correctly - the E820 had the same non-RAM regions and
> gaps - and the last RAM E820 entry was properly truncated. However, when it
> came to pure PV it was truncated more than it should:
> 
> domU:								domU:
> 0000000000000000 - 00000000000a0000 (usable)		0000000000000000 - 00000000000a0000 (usable)
> 00000000000a0000 - 0000000000100000 (reserved)	00000000000a0000 - 0000000000100000 (reserved)
> 0000000000100000 - 0000000040800000 (usable)	      |	0000000000100000 - 0000000040100000 (usable)
> 
> (left has the old PV - without your patch). Which makes me think that there is something
> amiss in the toolstack? I used 'xl' (latest xen-unstable from today).

What were you expecting? It looks like xl is either: specifying a memory
map that is larger than it should be or b) setting the maximum
reservation as too low.  And if you asked for 1 GiB neither looks right.

David