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    Subject[RFC V3 PATCH 05/25] node_states: introduce N_MEMORY
    We have N_NORMAL_MEMORY for standing for the nodes that have normal memory with
    zone_type <= ZONE_NORMAL.

    And we have N_HIGH_MEMORY for standing for the nodes that have normal or high

    But we don't have any word to stand for the nodes that have *any* memory.

    And we have N_CPU but without N_MEMORY.

    Current code reuse the N_HIGH_MEMORY for this purpose because any node which
    has memory must have high memory or normal memory currently.

    A) But this reusing is bad for *readability*. Because the name
    N_HIGH_MEMORY just stands for high or normal:

    A.example 1)
    for_each_node_state(nid, N_HIGH_MEMORY)

    The user will be confused(why this function just counts for high or
    normal memory node? does it counts for ZONE_MOVABLE's lru pages?)
    until someone else tell them N_HIGH_MEMORY is reused to stand for
    nodes that have any memory.

    A.cont) If we introduce N_MEMORY, we can reduce this confusing
    AND make the code more clearly:

    A.example 2) mm/page_cgroup.c use N_HIGH_MEMORY twice:

    One is in page_cgroup_init(void):
    for_each_node_state(nid, N_HIGH_MEMORY) {

    It means if the node have memory, we will allocate page_cgroup map for
    the node. We should use N_MEMORY instead here to gaim more clearly.

    The second using is in alloc_page_cgroup():
    if (node_state(nid, N_HIGH_MEMORY))
    addr = vzalloc_node(size, nid);

    It means if the node has high or normal memory that can be allocated
    from kernel. We should keep N_HIGH_MEMORY here, and it will be better
    if the "any memory" semantic of N_HIGH_MEMORY is removed.

    B) This reusing is out-dated if we introduce MOVABLE-dedicated node.
    The MOVABLE-dedicated node should not appear in
    node_stats[N_HIGH_MEMORY] nor node_stats[N_NORMAL_MEMORY],
    because MOVABLE-dedicated node has no high or normal memory.

    In x86_64, N_HIGH_MEMORY=N_NORMAL_MEMORY, if a MOVABLE-dedicated node
    is in node_stats[N_HIGH_MEMORY], it is also means it is in
    node_stats[N_NORMAL_MEMORY], it causes SLUB wrong.

    The slub uses
    for_each_node_state(nid, N_NORMAL_MEMORY)
    and creates kmem_cache_node for MOVABLE-dedicated node and cause problem.

    In one word, we need a N_MEMORY. We just intrude it as an alias to
    N_HIGH_MEMORY and fix all im-proper usages of N_HIGH_MEMORY in late patches.

    Signed-off-by: Lai Jiangshan <>
    Acked-by: Christoph Lameter <>
    Acked-by: Hillf Danton <>
    include/linux/nodemask.h | 1 +
    1 files changed, 1 insertions(+), 0 deletions(-)

    diff --git a/include/linux/nodemask.h b/include/linux/nodemask.h
    index 7afc363..c6ebdc9 100644
    --- a/include/linux/nodemask.h
    +++ b/include/linux/nodemask.h
    @@ -380,6 +380,7 @@ enum node_states {
    N_CPU, /* The node has one or more cpus */

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      Last update: 2012-08-06 12:01    [W:0.032 / U:13.916 seconds]
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