Re: [Xen-devel] [PATCH] delte PAGE_ORDER_1G in pod

["Zhang, Chunyu" <zhangcy@xxxxxxxxxxxxxx>]

>On 26/04/16 08:27, zhangcy wrote:
>> PoD does not have cache list for 1GB pages.
>> 
>> Signed-off-by: zhangcy <zhangcy@xxxxxxxxxxxxxx>
>
>Thanks for the patch.  FYI we normally tag the area in the title in a
>structured way; I probably would have used something like the following:
>
>xen/pod: Remove code handling PAGE_ORDER_1G from p2m_pod_cache_add
got it, thanks.
>
>But with regards to the patch itself: The question isn't whether we have
>a cache list for 1G pages; the question is whether p2m_pod_cache_add()
>will ever be called with order == PAGE_ORDER_1G.
>
>Taking a quick glance around, it looks like in theory if a guest called
>decrease_reservation with order == PAGE_ORDER_1G, you could conceivably
>get to p2m_pod_cache_add() with order == PAGE_ORDER_1G.
i just think like this:

p2m_pod_decrease_reservation 
  - if ( steal_for_cache && p2m_is_ram(t) )
     - p2m_pod_cache_add(p2m, page, cur_order)
i think p2m_is_ram(t) , ram also from pod cache,
pod cache is just 4k or 2M.
so i think ram is just 4k or 2M.

but i not sure about this...

>
>Even if the answer is "no", that may change in the future; which means
>we need to at very least add an ASSERT(), and possibly add a more robust
>failure case.  And at that point, since handling it properly only
>requires 4 lines, you might as well just handle it.
ok, thanks.

 - zhang
>
>Thanks,
> -George
>
>> ---
>>  xen/arch/x86/mm/p2m-pod.c | 4 ----
>>  1 file changed, 4 deletions(-)
>> 
>> diff --git a/xen/arch/x86/mm/p2m-pod.c b/xen/arch/x86/mm/p2m-pod.c
>> index a931f2c..89a07ee 100644
>> --- a/xen/arch/x86/mm/p2m-pod.c
>> +++ b/xen/arch/x86/mm/p2m-pod.c
>> @@ -122,10 +122,6 @@ p2m_pod_cache_add(struct p2m_domain *p2m,
>>      /* Then add to the appropriate populate-on-demand list. */
>>      switch ( order )
>>      {
>> -    case PAGE_ORDER_1G:
>> -        for ( i = 0; i < (1UL << PAGE_ORDER_1G); i += 1UL << PAGE_ORDER_2M )
>> -            page_list_add_tail(page + i, &p2m->pod.super);
>> -        break;
>>      case PAGE_ORDER_2M:
>>          page_list_add_tail(page, &p2m->pod.super);
>>          break;
>> 
>
>
>

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