Re: [Xen-devel] [PATCH] x86/PoD: skip eager reclaim when possible

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 10.05.16 at 15:44, <JBeulich@xxxxxxxx> wrote:
> Reclaiming pages is pointless when the cache can already satisfy all
> outstanding PoD entries, and doing reclaims in that case can be very
> harmful to performance when that memory gets used by the guest, but
> only to store zeroes there.
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

And I realize I forgot to Cc you, Wei.

Jan

> --- a/xen/arch/x86/mm/p2m-pod.c
> +++ b/xen/arch/x86/mm/p2m-pod.c
> @@ -1027,7 +1027,6 @@ static void pod_eager_record(struct p2m_
>  {
>      struct pod_mrp_list *mrp = &p2m->pod.mrp;
>  
> -    ASSERT(mrp->list[mrp->idx] == INVALID_GFN);
>      ASSERT(gfn != INVALID_GFN);
>  
>      mrp->list[mrp->idx++] =
> @@ -1075,7 +1074,9 @@ p2m_pod_demand_populate(struct p2m_domai
>          return 0;
>      }
>  
> -    pod_eager_reclaim(p2m);
> +    /* Only reclaim if we're in actual need of more cache. */
> +    if ( p2m->pod.entry_count > p2m->pod.count )
> +        pod_eager_reclaim(p2m);
>  
>      /* Only sweep if we're actually out of memory.  Doing anything else
>       * causes unnecessary time and fragmentation of superpages in the p2m. 
> */




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