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    Subject[PATCH net-next v7 1/1] net:openvswitch:reduce cpu_used_mask memory
    Date
    Use actual CPU number instead of hardcoded value to decide the size
    of 'cpu_used_mask' in 'struct sw_flow'. Below is the reason.

    'struct cpumask cpu_used_mask' is embedded in struct sw_flow.
    Its size is hardcoded to CONFIG_NR_CPUS bits, which can be
    8192 by default, it costs memory and slows down ovs_flow_alloc

    To address this:
    Redefine cpu_used_mask to pointer.
    Append cpumask_size() bytes after 'stat' to hold cpumask.
    Initialization cpu_used_mask right after stats_last_writer.

    APIs like cpumask_next and cpumask_set_cpu never access bits
    beyond cpu count, cpumask_size() bytes of memory is enough

    Signed-off-by: Eddy Tao <taoyuan_eddy@hotmail.com>
    ---
    net/openvswitch/flow.c | 9 ++++++---
    net/openvswitch/flow.h | 2 +-
    net/openvswitch/flow_table.c | 8 +++++---
    3 files changed, 12 insertions(+), 7 deletions(-)

    diff --git a/net/openvswitch/flow.c b/net/openvswitch/flow.c
    index e20d1a973417..416976f70322 100644
    --- a/net/openvswitch/flow.c
    +++ b/net/openvswitch/flow.c
    @@ -107,7 +107,8 @@ void ovs_flow_stats_update(struct sw_flow *flow, __be16 tcp_flags,

    rcu_assign_pointer(flow->stats[cpu],
    new_stats);
    - cpumask_set_cpu(cpu, &flow->cpu_used_mask);
    + cpumask_set_cpu(cpu,
    + flow->cpu_used_mask);
    goto unlock;
    }
    }
    @@ -135,7 +136,8 @@ void ovs_flow_stats_get(const struct sw_flow *flow,
    memset(ovs_stats, 0, sizeof(*ovs_stats));

    /* We open code this to make sure cpu 0 is always considered */
    - for (cpu = 0; cpu < nr_cpu_ids; cpu = cpumask_next(cpu, &flow->cpu_used_mask)) {
    + for (cpu = 0; cpu < nr_cpu_ids;
    + cpu = cpumask_next(cpu, flow->cpu_used_mask)) {
    struct sw_flow_stats *stats = rcu_dereference_ovsl(flow->stats[cpu]);

    if (stats) {
    @@ -159,7 +161,8 @@ void ovs_flow_stats_clear(struct sw_flow *flow)
    int cpu;

    /* We open code this to make sure cpu 0 is always considered */
    - for (cpu = 0; cpu < nr_cpu_ids; cpu = cpumask_next(cpu, &flow->cpu_used_mask)) {
    + for (cpu = 0; cpu < nr_cpu_ids;
    + cpu = cpumask_next(cpu, flow->cpu_used_mask)) {
    struct sw_flow_stats *stats = ovsl_dereference(flow->stats[cpu]);

    if (stats) {
    diff --git a/net/openvswitch/flow.h b/net/openvswitch/flow.h
    index 073ab73ffeaa..b5711aff6e76 100644
    --- a/net/openvswitch/flow.h
    +++ b/net/openvswitch/flow.h
    @@ -229,7 +229,7 @@ struct sw_flow {
    */
    struct sw_flow_key key;
    struct sw_flow_id id;
    - struct cpumask cpu_used_mask;
    + struct cpumask *cpu_used_mask;
    struct sw_flow_mask *mask;
    struct sw_flow_actions __rcu *sf_acts;
    struct sw_flow_stats __rcu *stats[]; /* One for each CPU. First one
    diff --git a/net/openvswitch/flow_table.c b/net/openvswitch/flow_table.c
    index 0a0e4c283f02..791504b7f42b 100644
    --- a/net/openvswitch/flow_table.c
    +++ b/net/openvswitch/flow_table.c
    @@ -79,6 +79,7 @@ struct sw_flow *ovs_flow_alloc(void)
    return ERR_PTR(-ENOMEM);

    flow->stats_last_writer = -1;
    + flow->cpu_used_mask = (struct cpumask *)&flow->stats[nr_cpu_ids];

    /* Initialize the default stat node. */
    stats = kmem_cache_alloc_node(flow_stats_cache,
    @@ -91,7 +92,7 @@ struct sw_flow *ovs_flow_alloc(void)

    RCU_INIT_POINTER(flow->stats[0], stats);

    - cpumask_set_cpu(0, &flow->cpu_used_mask);
    + cpumask_set_cpu(0, flow->cpu_used_mask);

    return flow;
    err:
    @@ -115,7 +116,7 @@ static void flow_free(struct sw_flow *flow)
    flow->sf_acts);
    /* We open code this to make sure cpu 0 is always considered */
    for (cpu = 0; cpu < nr_cpu_ids;
    - cpu = cpumask_next(cpu, &flow->cpu_used_mask)) {
    + cpu = cpumask_next(cpu, flow->cpu_used_mask)) {
    if (flow->stats[cpu])
    kmem_cache_free(flow_stats_cache,
    (struct sw_flow_stats __force *)flow->stats[cpu]);
    @@ -1196,7 +1197,8 @@ int ovs_flow_init(void)

    flow_cache = kmem_cache_create("sw_flow", sizeof(struct sw_flow)
    + (nr_cpu_ids
    - * sizeof(struct sw_flow_stats *)),
    + * sizeof(struct sw_flow_stats *))
    + + cpumask_size(),
    0, 0, NULL);
    if (flow_cache == NULL)
    return -ENOMEM;
    --
    2.27.0
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