From: KAMEZAWA Hiroyuki Documentation for numa_zonelist_order. Signed-off-by: KAMEZAWA Hiroyuki Cc: Lee Schermerhorn Cc: Christoph Lameter Cc: Andi Kleen Cc: "jesse.barnes@intel.com" Signed-off-by: Andrew Morton --- Documentation/kernel-parameters.txt | 5 ++ Documentation/sysctl/vm.txt | 46 ++++++++++++++++++++++++++ 2 files changed, 51 insertions(+) diff -puN Documentation/kernel-parameters.txt~change-zonelist-order-documentaion Documentation/kernel-parameters.txt --- a/Documentation/kernel-parameters.txt~change-zonelist-order-documentaion +++ a/Documentation/kernel-parameters.txt @@ -1244,6 +1244,11 @@ and is between 256 and 4096 characters. nowb [ARM] + numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. + one of ['zone', 'node', 'default'] can be specified + This can be set from sysctl after boot. + See Documentation/sysctl/vm.txt for details. + nr_uarts= [SERIAL] maximum number of UARTs to be registered. opl3= [HW,OSS] diff -puN Documentation/sysctl/vm.txt~change-zonelist-order-documentaion Documentation/sysctl/vm.txt --- a/Documentation/sysctl/vm.txt~change-zonelist-order-documentaion +++ a/Documentation/sysctl/vm.txt @@ -31,6 +31,7 @@ Currently, these files are in /proc/sys/ - min_unmapped_ratio - min_slab_ratio - panic_on_oom +- numa_zonelist_order ============================================================== @@ -216,3 +217,48 @@ above-mentioned. The default value is 0. 1 and 2 are for failover of clustering. Please select either according to your policy of failover. + +============================================================== + +numa_zonelist_order + +This sysctl is only for NUMA. +'where the memory is allocated from' is controlled by zonelists. +(This documentation ignores ZONE_HIGHMEM/ZONE_DMA32 for simple explanation. + you may be able to read ZONE_DMA as ZONE_DMA32...) + +In non-NUMA case, a zonelist for GFP_KERNEL is ordered as following. +ZONE_NORMAL -> ZONE_DMA +This means that a memory allocation request for GFP_KERNEL will +get memory from ZONE_DMA only when ZONE_NORMAL is not available. + +In NUMA case, you can think of following 2 types of order. +Assume 2 node NUMA and below is zonelist of Node(0)'s GFP_KERNEL + +(A) Node(0) ZONE_NORMAL -> Node(0) ZONE_DMA -> Node(1) ZONE_NORMAL +(B) Node(0) ZONE_NORMAL -> Node(1) ZONE_NORMAL -> Node(0) ZONE_DMA. + +Type(A) offers the best locality for processes on Node(0), but ZONE_DMA +will be used before ZONE_NORMAL exhaustion. This increases possibility of +out-of-memory(OOM) of ZONE_DMA because ZONE_DMA is tend to be small. + +Type(B) cannot offer the best locality but is more robust against OOM of +the DMA zone. + +Type(A) is called as "Node" order. Type (B) is "Zone" order. + +"Node order" orders the zonelists by node, then by zone within each node. +Specify "[Nn]ode" for zone order + +"Zone Order" orders the zonelists by zone type, then by node within each +zone. Specify "[Zz]one"for zode order. + +Specify "[Dd]efault" to request automatic configuration. Autoconfiguration +will select "node" order in following case. +(1) if the DMA zone does not exist or +(2) if the DMA zone comprises greater than 50% of the available memory or +(3) if any node's DMA zone comprises greater than 60% of its local memory and + the amount of local memory is big enough. + +Otherwise, "zone" order will be selected. Default order is recommended unless +this is causing problems for your system/application. _