On Fri, Feb 19, 2010 at 3:59 AM, Anton Blanchard [off-list ref] wrote:

I noticed /proc/sys/vm/zone_reclaim_mode was 0 on a ppc64 NUMA box. It ge=

ts

enabled via this:

=A0 =A0 =A0 =A0/*
=A0 =A0 =A0 =A0 * If another node is sufficiently far away then it is bet=

ter

=A0 =A0 =A0 =A0 * to reclaim pages in a zone before going off node.
=A0 =A0 =A0 =A0 */
=A0 =A0 =A0 =A0if (distance > RECLAIM_DISTANCE)
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0zone_reclaim_mode =3D 1;

Since we use the default value of 20 for REMOTE_DISTANCE and 20 for
RECLAIM_DISTANCE it never kicks in.

The local to remote bandwidth ratios can be quite large on System p
machines so it makes sense for us to reclaim clean pagecache locally befo=

re

going off node.

The patch below sets a smaller value for RECLAIM_DISTANCE and thus enable=

s

zone reclaim.

A reclaim distance of 10 implies a ratio of 1, that means we'll always
do zone_reclaim() to free page cache and slab cache before moving on
to another node?

Balbir Singh.