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

KOSAKI Motohiro
2009-05-14T12:02:54Z

> > Unfortunately no.
> > zone reclaim has two weakness by design.
> >
> > 1.
> > zone reclaim don't works well when workingset size > local node size.
> > but it can happen easily on small machine.
> > if it happen, zone reclaim drop own process's memory.
> >
> > Plus, zone reclaim also doesn't fit DB server. its process has large
> > workingset.
>
> Large DB server is not your typical desktop application either.

ack.

> > 2.
> > zone reclaim have inter zone balancing issue.
> >
> > example: x86_64 2node 8G machine has following zone assignment
> >
> > zone 0 (DMA32): 3GB
> > zone 0 (Normal): 1GB
> > zone 1 (Normal): 4GB
> >
> > if the page is allocated from DMA32, you are lucky. DMA32 isn't reclaimed
> > so freqently. but if from zone0 Normal, you are unlucky.
> > it is very frequent reclaimed although it is small than other zone.
>
> I have seen that behavior on some of our mismatched large systems as well,
> although never had one so imbalanced because ia64 only has Normal.

not true.
some ia64 server has about 2GB DMA zone. SGI ia64 is special one.

> > I know my patch change large server default. but I believe linux
> > default kernel parameter adapt to desktop and entry machine.
>
> If this imbalance is an x86_64 only problem, then we could do something
> simple like the following untested patch. This leaves the default
> for everyone except x86_64.

not x86_64 only.
many 64bit architecture have 2 or 4GB DMA zone.

even though, your patch seems interesting. at least it solve
desktop user issue and we don't need to care another area user.

embedded and high-end server user is typically skillfull. they can
change kernel parameter by themself.

>
> Robin
>
> ------------------------------------------------------------------------
>
> Even if there is a great node distance on x86_64, disable zone reclaim
> by default. This was done to handle the imbalanced zone sizes where a
> majority of the memory in zone 0 is DMA32 with a small remaining Normal
> which will be aggressively reclaimed.
>
> For other architectures, we leave the default behavior.
>
> Signed-off-by: Robin Holt <holt@sgi.com>
> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> Cc: Christoph Lameter <cl@linux-foundation.org>
> Cc: Rik van Riel <riel@redhat.com>
>
> ---
> arch/x86/include/asm/topology.h | 2 ++
> include/linux/topology.h | 5 +++++
> mm/page_alloc.c | 2 +-
> 3 files changed, 8 insertions(+), 1 deletion(-)
> Index: page_reclaim_mode/arch/x86/include/asm/topology.h
> ===================================================================
> --- page_reclaim_mode.orig/arch/x86/include/asm/topology.h 2009-05-14 06:44:20.118925713 -0500
> +++ page_reclaim_mode/arch/x86/include/asm/topology.h 2009-05-14 06:44:21.251067716 -0500
> @@ -128,6 +128,8 @@ extern unsigned long node_remap_size[];
>
> #endif
>
> +#define DEFAULT_ZONE_RECLAIM_MODE 0
> +
> /* sched_domains SD_NODE_INIT for NUMA machines */
> #define SD_NODE_INIT (struct sched_domain) { \
> .min_interval = 8, \
> Index: page_reclaim_mode/include/linux/topology.h
> ===================================================================
> --- page_reclaim_mode.orig/include/linux/topology.h 2009-05-14 06:44:20.070919619 -0500
> +++ page_reclaim_mode/include/linux/topology.h 2009-05-14 06:44:21.279071382 -0500
> @@ -61,6 +61,11 @@ int arch_update_cpu_topology(void);
> */
> #define RECLAIM_DISTANCE 20
> #endif
> +
> +#ifndef DEFAULT_ZONE_RECLAIM_MODE
> +#define DEFAULT_ZONE_RECLAIM_MODE 1
> +#endif
> +
> #ifndef PENALTY_FOR_NODE_WITH_CPUS
> #define PENALTY_FOR_NODE_WITH_CPUS (1)
> #endif
> Index: page_reclaim_mode/mm/page_alloc.c
> ===================================================================
> --- page_reclaim_mode.orig/mm/page_alloc.c 2009-05-14 06:44:20.138928363 -0500
> +++ page_reclaim_mode/mm/page_alloc.c 2009-05-14 06:44:21.311075244 -0500
> @@ -2331,7 +2331,7 @@ static void build_zonelists(pg_data_t *p
> * to reclaim pages in a zone before going off node.
> */
> if (distance > RECLAIM_DISTANCE)
> - zone_reclaim_mode = 1;
> + zone_reclaim_mode = DEFAULT_ZONE_RECLAIM_MODE;
>
> /*
> * We don't want to pressure a particular node.