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    Subject[PATCH 3/6] numa,sched: build per numa_group active node mask from faults_from statistics
    Date
    From: Rik van Riel <riel@redhat.com>

    The faults_from statistics are used to maintain an active_nodes nodemask
    per numa_group. This allows us to be smarter about when to do numa migrations.

    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Mel Gorman <mgorman@suse.de>
    Cc: Ingo Molnar <mingo@redhat.com>
    Cc: Chegu Vinod <chegu_vinod@hp.com>
    Signed-off-by: Rik van Riel <riel@redhat.com>
    ---
    kernel/sched/fair.c | 41 +++++++++++++++++++++++++++++++++++++++++
    1 file changed, 41 insertions(+)

    diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
    index 1945ddc..ea8b2ae 100644
    --- a/kernel/sched/fair.c
    +++ b/kernel/sched/fair.c
    @@ -885,6 +885,7 @@ struct numa_group {
    struct list_head task_list;

    struct rcu_head rcu;
    + nodemask_t active_nodes;
    unsigned long total_faults;
    unsigned long *faults_from;
    unsigned long faults[0];
    @@ -1275,6 +1276,41 @@ static void numa_migrate_preferred(struct task_struct *p)
    }

    /*
    + * Find the nodes on which the workload is actively running. We do this by
    + * tracking the nodes from which NUMA hinting faults are triggered. This can
    + * be different from the set of nodes where the workload's memory is currently
    + * located.
    + *
    + * The bitmask is used to make smarter decisions on when to do NUMA page
    + * migrations, To prevent flip-flopping, and excessive page migrations, nodes
    + * are added when they cause over 6/16 of the maximum number of faults, but
    + * only removed when they drop below 3/16.
    + */
    +static void update_numa_active_node_mask(struct task_struct *p)
    +{
    + unsigned long faults, max_faults = 0;
    + struct numa_group *numa_group = p->numa_group;
    + int nid;
    +
    + for_each_online_node(nid) {
    + faults = numa_group->faults_from[task_faults_idx(nid, 0)] +
    + numa_group->faults_from[task_faults_idx(nid, 1)];
    + if (faults > max_faults)
    + max_faults = faults;
    + }
    +
    + for_each_online_node(nid) {
    + faults = numa_group->faults_from[task_faults_idx(nid, 0)] +
    + numa_group->faults_from[task_faults_idx(nid, 1)];
    + if (!node_isset(nid, numa_group->active_nodes)) {
    + if (faults > max_faults * 6 / 16)
    + node_set(nid, numa_group->active_nodes);
    + } else if (faults < max_faults * 3 / 16)
    + node_clear(nid, numa_group->active_nodes);
    + }
    +}
    +
    +/*
    * When adapting the scan rate, the period is divided into NUMA_PERIOD_SLOTS
    * increments. The more local the fault statistics are, the higher the scan
    * period will be for the next scan window. If local/remote ratio is below
    @@ -1416,6 +1452,7 @@ static void task_numa_placement(struct task_struct *p)
    update_task_scan_period(p, fault_types[0], fault_types[1]);

    if (p->numa_group) {
    + update_numa_active_node_mask(p);
    /*
    * If the preferred task and group nids are different,
    * iterate over the nodes again to find the best place.
    @@ -1478,6 +1515,8 @@ static void task_numa_group(struct task_struct *p, int cpupid, int flags,
    /* Second half of the array tracks where faults come from */
    grp->faults_from = grp->faults + 2 * nr_node_ids;

    + node_set(task_node(current), grp->active_nodes);
    +
    for (i = 0; i < 4*nr_node_ids; i++)
    grp->faults[i] = p->numa_faults[i];

    @@ -1547,6 +1586,8 @@ static void task_numa_group(struct task_struct *p, int cpupid, int flags,
    my_grp->nr_tasks--;
    grp->nr_tasks++;

    + update_numa_active_node_mask(p);
    +
    spin_unlock(&my_grp->lock);
    spin_unlock(&grp->lock);

    --
    1.8.4.2


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