Re: [Xen-devel] [PATCH] x86/mm: Ensure useful progress in alloc_l2_table()

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 03.07.13 at 13:37, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
> --- a/xen/arch/x86/mm.c
> +++ b/xen/arch/x86/mm.c
> @@ -1278,13 +1278,6 @@ static int alloc_l2_table(struct page_info *page, 
> unsigned long type,
>  
>      for ( i = page->nr_validated_ptes; i < L2_PAGETABLE_ENTRIES; i++ )
>      {
> -        if ( preemptible && i && hypercall_preempt_check() )
> -        {
> -            page->nr_validated_ptes = i;
> -            rc = -EAGAIN;
> -            break;
> -        }
> -
>          if ( !is_guest_l2_slot(d, type, i) ||
>               (rc = get_page_from_l2e(pl2e[i], pfn, d)) > 0 )
>              continue;
> @@ -1299,6 +1292,14 @@ static int alloc_l2_table(struct page_info *page, 
> unsigned long type,
>          }
>  
>          adjust_guest_l2e(pl2e[i], d);
> +
> +        if ( preemptible && i != L2_PAGETABLE_ENTRIES

        if ( preemptible && i != L2_PAGETABLE_ENTRIES - 1

But an even smaller change would be to change the if() you remove 
above to

        if ( preemptible && i > page->nr_validated_ptes &&
            hypercall_preempt_check() )

Jan

> +             && hypercall_preempt_check() )
> +        {
> +            page->nr_validated_ptes = i + 1;
> +            rc = -EAGAIN;
> +            break;
> +        }
>      }
>  
>      if ( rc >= 0 && (type & PGT_pae_xen_l2) )



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