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    SubjectRe: [PATCH 20/35] Use a pre-calculated value for num_online_nodes()
    On Thu, Mar 19, 2009 at 04:43:55PM -0400, Christoph Lameter wrote:
    > Trying to the same in the style of nr_node_ids etc.
    >

    Because of some issues with the patch and what it does for possible
    nodes, I reworked the patch slightly into the following and is what I'm
    actually testing.

    commit 58652d22798591d4df5421a90d65cbd7e60b9048
    Author: Christoph Lameter <cl@linux-foundation.org>
    Date: Thu Mar 19 21:34:17 2009 +0000

    Use a pre-calculated value for num_online_nodes()

    num_online_nodes() is called in a number of places but most often by the
    page allocator when deciding whether the zonelist needs to be filtered based
    on cpusets or the zonelist cache. This is actually a heavy function and
    touches a number of cache lines. This patch stores the number of online
    nodes at boot time and updates the value when nodes get onlined and offlined.

    Signed-off-by: Christoph Lameter <cl@linux-foundation.org>
    Signed-off-by: Mel Gorman <mel@csn.ul.ie>

    diff --git a/include/linux/nodemask.h b/include/linux/nodemask.h
    index 848025c..474e73e 100644
    --- a/include/linux/nodemask.h
    +++ b/include/linux/nodemask.h
    @@ -408,6 +408,19 @@ static inline int num_node_state(enum node_states state)
    #define next_online_node(nid) next_node((nid), node_states[N_ONLINE])

    extern int nr_node_ids;
    +extern int nr_online_nodes;
    +
    +static inline void node_set_online(int nid)
    +{
    + node_set_state(nid, N_ONLINE);
    + nr_online_nodes = num_node_state(N_ONLINE);
    +}
    +
    +static inline void node_set_offline(int nid)
    +{
    + node_clear_state(nid, N_ONLINE);
    + nr_online_nodes = num_node_state(N_ONLINE);
    +}
    #else

    static inline int node_state(int node, enum node_states state)
    @@ -434,7 +447,7 @@ static inline int num_node_state(enum node_states state)
    #define first_online_node 0
    #define next_online_node(nid) (MAX_NUMNODES)
    #define nr_node_ids 1
    -
    +#define nr_online_nodes 1
    #endif

    #define node_online_map node_states[N_ONLINE]
    diff --git a/mm/hugetlb.c b/mm/hugetlb.c
    index 1e99997..210e28c 100644
    --- a/mm/hugetlb.c
    +++ b/mm/hugetlb.c
    @@ -875,7 +875,7 @@ static void return_unused_surplus_pages(struct hstate *h,
    * can no longer free unreserved surplus pages. This occurs when
    * the nodes with surplus pages have no free pages.
    */
    - unsigned long remaining_iterations = num_online_nodes();
    + unsigned long remaining_iterations = nr_online_nodes;

    /* Uncommit the reservation */
    h->resv_huge_pages -= unused_resv_pages;
    @@ -904,7 +904,7 @@ static void return_unused_surplus_pages(struct hstate *h,
    h->surplus_huge_pages--;
    h->surplus_huge_pages_node[nid]--;
    nr_pages--;
    - remaining_iterations = num_online_nodes();
    + remaining_iterations = nr_online_nodes;
    }
    }
    }
    diff --git a/mm/page_alloc.c b/mm/page_alloc.c
    index 18f0b56..4131ff9 100644
    --- a/mm/page_alloc.c
    +++ b/mm/page_alloc.c
    @@ -164,7 +164,9 @@ static unsigned long __meminitdata dma_reserve;

    #if MAX_NUMNODES > 1
    int nr_node_ids __read_mostly = MAX_NUMNODES;
    +int nr_online_nodes __read_mostly = 1;
    EXPORT_SYMBOL(nr_node_ids);
    +EXPORT_SYMBOL(nr_online_nodes);
    #endif

    int page_group_by_mobility_disabled __read_mostly;
    @@ -1445,7 +1447,7 @@ get_page_from_freelist(gfp_t gfp_mask, nodemask_t *nodemask, unsigned int order,
    /* Determine in advance if the zonelist needs filtering */
    if ((alloc_flags & ALLOC_CPUSET) && unlikely(number_of_cpusets > 1))
    zonelist_filter = 1;
    - if (num_online_nodes() > 1)
    + if (nr_online_nodes > 1)
    zonelist_filter = 1;

    zonelist_scan:
    @@ -1486,7 +1488,7 @@ this_zone_full:
    zlc_mark_zone_full(zonelist, z);
    try_next_zone:
    if (NUMA_BUILD && zonelist_filter) {
    - if (!did_zlc_setup && num_online_nodes() > 1) {
    + if (!did_zlc_setup && nr_online_nodes > 1) {
    /*
    * do zlc_setup after the first zone is tried
    * but only if there are multiple nodes to make
    @@ -2285,7 +2287,7 @@ int numa_zonelist_order_handler(ctl_table *table, int write,
    }


    -#define MAX_NODE_LOAD (num_online_nodes())
    +#define MAX_NODE_LOAD (nr_online_nodes)
    static int node_load[MAX_NUMNODES];

    /**
    @@ -2494,7 +2496,7 @@ static void build_zonelists(pg_data_t *pgdat)

    /* NUMA-aware ordering of nodes */
    local_node = pgdat->node_id;
    - load = num_online_nodes();
    + load = nr_online_nodes;
    prev_node = local_node;
    nodes_clear(used_mask);

    @@ -2645,7 +2647,7 @@ void build_all_zonelists(void)

    printk("Built %i zonelists in %s order, mobility grouping %s. "
    "Total pages: %ld\n",
    - num_online_nodes(),
    + nr_online_nodes,
    zonelist_order_name[current_zonelist_order],
    page_group_by_mobility_disabled ? "off" : "on",
    vm_total_pages);
    diff --git a/mm/slab.c b/mm/slab.c
    index e7f1ded..e6157a0 100644
    --- a/mm/slab.c
    +++ b/mm/slab.c
    @@ -3526,7 +3526,7 @@ static inline void __cache_free(struct kmem_cache *cachep, void *objp)
    * variable to skip the call, which is mostly likely to be present in
    * the cache.
    */
    - if (numa_platform && cache_free_alien(cachep, objp))
    + if (numa_platform > 1 && cache_free_alien(cachep, objp))
    return;

    if (likely(ac->avail < ac->limit)) {
    diff --git a/mm/slub.c b/mm/slub.c
    index 0280eee..8ce6be8 100644
    --- a/mm/slub.c
    +++ b/mm/slub.c
    @@ -3648,7 +3648,7 @@ static int list_locations(struct kmem_cache *s, char *buf,
    to_cpumask(l->cpus));
    }

    - if (num_online_nodes() > 1 && !nodes_empty(l->nodes) &&
    + if (nr_online_nodes > 1 && !nodes_empty(l->nodes) &&
    len < PAGE_SIZE - 60) {
    len += sprintf(buf + len, " nodes=");
    len += nodelist_scnprintf(buf + len, PAGE_SIZE - len - 50,
    diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
    index c51fed4..ba9eb8f 100644
    --- a/net/sunrpc/svc.c
    +++ b/net/sunrpc/svc.c
    @@ -124,7 +124,7 @@ svc_pool_map_choose_mode(void)
    {
    unsigned int node;

    - if (num_online_nodes() > 1) {
    + if (nr_online_nodes > 1) {
    /*
    * Actually have multiple NUMA nodes,
    * so split pools on NUMA node boundaries

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