Re: [Xen-devel] [RFC PATCH V2 1/4] xen/hap: Increase hap page pool size for more vcpus support

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 01.09.17 at 10:19, <tianyu.lan@xxxxxxxxx> wrote:
> On 2017年08月31日 21:56, Andrew Cooper wrote:
>> On 31/08/17 06:01, Lan Tianyu wrote:
>>> This patch is to increase hap page pool size to support more vcpus in 
>>> single 
> VM.
>>>
>>> Signed-off-by: Lan Tianyu <tianyu.lan@xxxxxxxxx>
>>> ---
>>>  xen/arch/x86/mm/hap/hap.c | 10 +++++++++-
>>>  1 file changed, 9 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/xen/arch/x86/mm/hap/hap.c b/xen/arch/x86/mm/hap/hap.c
>>> index cdc77a9..96a7ed0 100644
>>> --- a/xen/arch/x86/mm/hap/hap.c
>>> +++ b/xen/arch/x86/mm/hap/hap.c
>>> @@ -464,6 +464,7 @@ void hap_domain_init(struct domain *d)
>>>  int hap_enable(struct domain *d, u32 mode)
>>>  {
>>>      unsigned int old_pages;
>>> +    unsigned int pages;
>>>      unsigned int i;
>>>      int rv = 0;
>>>  
>>> @@ -473,7 +474,14 @@ int hap_enable(struct domain *d, u32 mode)
>>>      if ( old_pages == 0 )
>>>      {
>>>          paging_lock(d);
>>> -        rv = hap_set_allocation(d, 256, NULL);
>>> +
>>> +        /* Increase hap page pool with max vcpu number. */
>>> +        if ( d->max_vcpus > 128 )
>>> +            pages = 256;
>>> +        else
>>> +            pages = 512;
>>> +
>>> +        rv = hap_set_allocation(d, pages, NULL);
>> 
>> What effect is this intended to have?  hap_enable() is always called
>> when d->max_vcpus is 0.
> 
> Sorry. I didn't notice that max_vcpus wasn't set at that point.I hope to
> allocate hap pages according vcpu number. This means we don't know how
> many vcpu will be used when allocate hap pages during creating domain,
> right? If that, we have to increase page number unconditionally.

But that you were already told isn't really acceptable. Did you
consider calling hap_set_allocation() another time once vCPU
count was set?

Jan

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