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    Subject[PATCH] change zonelist order v5 [3/3] documentation
    Patch for documentation.

    Signed-Off-By: KAMEZAWA hiroyuki <>

    Documentation/kernel-parameters.txt | 10 +++++++
    Documentation/sysctl/vm.txt | 48 ++++++++++++++++++++++++++++++++++++
    2 files changed, 58 insertions(+)

    Index: linux-2.6.21-mm1/Documentation/kernel-parameters.txt
    --- linux-2.6.21-mm1.orig/Documentation/kernel-parameters.txt
    +++ linux-2.6.21-mm1/Documentation/kernel-parameters.txt
    @@ -1233,6 +1233,16 @@ and is between 256 and 4096 characters.

    nr_uarts= [SERIAL] maximum number of UARTs to be registered.

    + numa_zonelist_oder= [KNL,BOOT]
    + Select zonelist order for NUMA. zonelist is used for
    + desiding where the kernel allocates memory from.
    + Default is automatic configuration. If "node" is
    + specified, zonelist is ordered by locality. This can
    + offer the best locality but possibility of OOM may
    + increase. If "zone" is specified, the zonelist is
    + ordered by zone_type.
    + See Documentaion/sysctl/vm.txt numa_zonelist_order.
    opl3= [HW,OSS]
    Format: <io>

    Index: linux-2.6.21-mm1/Documentation/sysctl/vm.txt
    --- linux-2.6.21-mm1.orig/Documentation/sysctl/vm.txt
    +++ linux-2.6.21-mm1/Documentation/sysctl/vm.txt
    @@ -35,6 +35,7 @@ Currently, these files are in /proc/sys/
    - stat_interval
    - readahead_ratio
    - readahead_hit_rate
    +- numa_zonelist_order


    @@ -293,3 +294,49 @@ Possible values can be:
    The larger value, the more capabilities, with more possible overheads.

    The default value is 1.
    +This sysctl is only for NUMA.
    +'where the memory is allocated from' is controlled by zonelist.
    +(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.
    +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 very robust against OOM of 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.
    +This will offer the best locality but increases possibility of OOM.
    +Specify "[Nn]ode" for zone order
    +"Zone Order" preserves the DMA zone as long as possible but
    +results in off-node allocation [for node 0] earlier.
    +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 a node's DMA zone comprises greater than 60% of its local memory and
    + the amount of local memory is enough big.
    +Otherwise, "zone" order will be selected. Default order is recommended unless
    +unless this is causing problems for your system/application.
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