Messages in this thread Patch in this message | | | Date | Thu, 14 May 2009 06:48:27 -0500 | From | Robin Holt <> | Subject | Re: [PATCH 4/4] zone_reclaim_mode is always 0 by default |
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> 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.
> 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.
> 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.
Robin
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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.
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