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SubjectRe: [PATCH v4] zone_reclaim is always 0 by default
On Thu, Jun 04, 2009 at 06:23:15PM +0800, KOSAKI Motohiro wrote:
>
> Current linux policy is, zone_reclaim_mode is enabled by default if the machine
> has large remote node distance. it's because we could assume that large distance
> mean large server until recently.
>
> Unfortunately, recent modern x86 CPU (e.g. Core i7, Opeteron) have P2P transport
> memory controller. IOW it's seen as NUMA from software view.
> Some Core i7 machine has large remote node distance.
>
> Yanmin reported zone_reclaim_mode=1 cause large apache regression.
>
> One Nehalem machine has 12GB memory,
> but there is always 2GB free although applications accesses lots of files.
> Eventually we located the root cause as zone_reclaim_mode=1.
>
> Actually, zone_reclaim_mode=1 mean "I dislike remote node allocation rather than
> disk access", it makes performance improvement to HPC workload.
> but it makes performance degression to desktop, file server and web server.
>
> In general, workload depended configration shouldn't put into default settings.
>
> However, current code is long standing about two year. Highest POWER and IA64 HPC machine
> (only) use this setting.
>
> Thus, x86 and almost rest architecture change default setting, but Only power and ia64
> remain current configuration for backward-compatibility.

The above lines are too long. Limit to 72 cols in general could be
better as git-log may add additional leading white spaces.

Thank you for all the efforts!

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>
> Cc: Robin Holt <holt@sgi.com>
> Cc: "Zhang, Yanmin" <yanmin.zhang@intel.com>
> Cc: Wu Fengguang <fengguang.wu@intel.com>
> Cc: linux-ia64@vger.kernel.org
> Cc: linuxppc-dev@ozlabs.org
> ---
> arch/powerpc/include/asm/topology.h | 6 ++++++
> include/linux/topology.h | 7 +------
> 2 files changed, 7 insertions(+), 6 deletions(-)
>
> Index: b/include/linux/topology.h
> ===================================================================
> --- a/include/linux/topology.h
> +++ b/include/linux/topology.h
> @@ -54,12 +54,7 @@ int arch_update_cpu_topology(void);
> #define node_distance(from,to) ((from) == (to) ? LOCAL_DISTANCE : REMOTE_DISTANCE)
> #endif
> #ifndef RECLAIM_DISTANCE
> -/*
> - * If the distance between nodes in a system is larger than RECLAIM_DISTANCE
> - * (in whatever arch specific measurement units returned by node_distance())
> - * then switch on zone reclaim on boot.
> - */
> -#define RECLAIM_DISTANCE 20
> +#define RECLAIM_DISTANCE INT_MAX
> #endif
> #ifndef PENALTY_FOR_NODE_WITH_CPUS
> #define PENALTY_FOR_NODE_WITH_CPUS (1)
> Index: b/arch/powerpc/include/asm/topology.h
> ===================================================================
> --- a/arch/powerpc/include/asm/topology.h
> +++ b/arch/powerpc/include/asm/topology.h
> @@ -10,6 +10,12 @@ struct device_node;
>
> #include <asm/mmzone.h>
>
> +/*
> + * Distance above which we begin to use zone reclaim

s/begin to/default to/ ?

> + */
> +#define RECLAIM_DISTANCE 20
> +
> +
> static inline int cpu_to_node(int cpu)
> {
> return numa_cpu_lookup_table[cpu];
>


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