Re: [PATCH 1/2] mm: Disable zone_reclaim_mode by default

[Mel Gorman <mgorman@suse.de>]

On Tue, Apr 08, 2014 at 09:14:05AM -0500, Christoph Lameter wrote:
> On Mon, 7 Apr 2014, Mel Gorman wrote:
> 
> > zone_reclaim_mode causes processes to prefer reclaiming memory from local
> > node instead of spilling over to other nodes. This made sense initially when
> > NUMA machines were almost exclusively HPC and the workload was partitioned
> > into nodes. The NUMA penalties were sufficiently high to justify reclaiming
> > the memory. On current machines and workloads it is often the case that
> > zone_reclaim_mode destroys performance but not all users know how to detect
> > this. Favour the common case and disable it by default. Users that are
> > sophisticated enough to know they need zone_reclaim_mode will detect it.
> 
> Ok that is going to require SGI machines to deal with zone_reclaim
> configurations on bootup. Dimitri? Any comments?
> 

The SGI machines are also likely to be managed by system administrators
who are both aware of zone_reclaim_mode and know how to evaluate if it
should be enabled or not. The pair of patches is really aimmed at the
common case of 2-8 socket machines running workloads that are not NUMA
aware.

-- 
Mel Gorman
SUSE Labs