On Thu, Mar 25, 2010 at 03:33:08PM -0700, David Rientjes wrote:
> There are two types of zonelist ordering methodologies:
>
> - node order, preferring allocations on a node to stay local to and
>
> - zone order, preferring allocations come from a higher zone to avoid
> allocating in lowmem zones even though they may not be local.
>
> The ordering technique used by the kernel is configurable on the command
> line, but also has some logic to determine what the default should be.
>
> This logic currently lacks knowledge of systems where a node may only
> have lowmem. For such systems, it is necessary to use node order so that
> GFP_KERNEL allocations may be satisfied by nodes consisting of only
> lowmem.
>
> If zone order is used, GFP_KERNEL allocations to such nodes are actually
> allocated on a node with local affinity that includes ZONE_NORMAL.
>
> This change defaults to node zonelist ordering if any node lacks
> ZONE_NORMAL.
>
> To force zone order, append 'numa_zonelist_order=zone' to the kernel
> command line.
>
> Cc: Mel Gorman <mel@xxxxxxxxx>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
> ---
> mm/page_alloc.c | 11 ++++++++++-
> 1 files changed, 10 insertions(+), 1 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2582,7 +2582,7 @@ static int default_zonelist_order(void)
> * ZONE_DMA and ZONE_DMA32 can be very small area in the sytem.
> * If they are really small and used heavily, the system can fall
> * into OOM very easily.
> - * This function detect ZONE_DMA/DMA32 size and confgigures zone order.
> + * This function detect ZONE_DMA/DMA32 size and configures zone order.
> */
Spurious change here but it's not very important.
> /* Is there ZONE_NORMAL ? (ex. ppc has only DMA zone..) */
> low_kmem_size = 0;
> @@ -2594,6 +2594,15 @@ static int default_zonelist_order(void)
> if (zone_type < ZONE_NORMAL)
> low_kmem_size += z->present_pages;
> total_size += z->present_pages;
> + } else if (zone_type == ZONE_NORMAL) {
> + /*
What if it was ZONE_DMA32?
> + * If any node has only lowmem, then node order
> + * is preferred to allow kernel allocations
> + * locally; otherwise, they can easily infringe
> + * on other nodes when there is an abundance of
> + * lowmem available to allocate from.
> + */
> + return ZONELIST_ORDER_NODE;
It might be clearer if it was done as a similar check later
if (low_kmem_size &&
total_size > average_size && /* ignore small node */
low_kmem_size > total_size * 70/100)
return ZONELIST_ORDER_NODE;
This is saying if low memory is > 70% of total, then use nodes. To take
yours into account, it'd look something like;
if (low_kmwm_size && total_size > average_size) {
if (lowmem_size == total_size)
return ZONELIST_ORDER_ZONE;
if (lowmem_size > total_size * 70/100)
return ZONELIST_ORDER_NODE;
}
> }
> }
> }
>
--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab
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