Re: [PATCH 4/4] zone_reclaim_mode is always 0 by default

Wu Fengguang
2009-05-18T03:49:57Z

On Wed, May 13, 2009 at 12:08:12PM +0900, KOSAKI Motohiro wrote:
> Subject: [PATCH] zone_reclaim_mode is always 0 by default
>
> Current linux policy is, if the machine has large remote node distance,
> zone_reclaim_mode is enabled by default because we've be able to assume to
> large distance mean large server until recently.
>
> Unfrotunately, recent modern x86 CPU (e.g. Core i7, Opeteron) have P2P transport
> memory controller. IOW it's NUMA from software view.
>
> Some Core i7 machine has large remote node distance and zone_reclaim don't
> fit desktop and small file server. it cause performance degression.

I can confirm this, Yanmin recently ran into exactly such a
regression, which was fixed by manually disabling the zone reclaim
mode. So I guess you can safely add an

Tested-by: "Zhang, Yanmin" <yanmin.zhang@intel.com>

> Thus, zone_reclaim == 0 is better by default. sorry, HPC gusy.
> you need to turn zone_reclaim_mode on manually now.

I guess the borderline will continue to blur up. It will be more
dependent on workloads instead of physical NUMA capabilities. So

Acked-by: Wu Fengguang <fengguang.wu@intel.com>

> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> Cc: Christoph Lameter <cl@linux-foundation.org>
> Cc: Rik van Riel <riel@redhat.com>
> ---
> mm/page_alloc.c | 7 -------
> 1 file changed, 7 deletions(-)
>
> Index: b/mm/page_alloc.c
> ===================================================================
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2494,13 +2494,6 @@ static void build_zonelists(pg_data_t *p
> int distance = node_distance(local_node, node);
>
> /*
> - * If another node is sufficiently far away then it is better
> - * to reclaim pages in a zone before going off node.
> - */
> - if (distance > RECLAIM_DISTANCE)
> - zone_reclaim_mode = 1;
> -
> - /*
> * We don't want to pressure a particular node.
> * So adding penalty to the first node in same
> * distance group to make it round-robin.
>
>
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