[PATCH v2 1/1] net: openvswitch: reduce cpu_used_mask memory

taoyuan_eddy
2023-02-01T13:25:11Z

From: Eddy Tao <taoyuan_eddy@hotmail.com>

'struct cpumask cpu_used_mask' is embedded in struct sw_flow.
However, its size is hardcoded to CONFIG_NR_CPUS bits, which can be
8192 by default, it costs memory and slows down ovs_flow_alloc.
This fix uses actual CPU number instead

Signed-off-by: Eddy Tao <taoyuan_eddy@hotmail.com>
---
net/openvswitch/flow.c | 6 +++---
net/openvswitch/flow.h | 2 +-
net/openvswitch/flow_table.c | 24 +++++++++++++++++++++---
3 files changed, 25 insertions(+), 7 deletions(-)

diff --git a/net/openvswitch/flow.c b/net/openvswitch/flow.c
index e20d1a973417..06345cd8c777 100644
--- a/net/openvswitch/flow.c
+++ b/net/openvswitch/flow.c
@@ -107,7 +107,7 @@ 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 +135,7 @@ 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 +159,7 @@ 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..63c95c9a814d 100644
--- a/net/openvswitch/flow_table.c
+++ b/net/openvswitch/flow_table.c
@@ -87,11 +87,12 @@ struct sw_flow *ovs_flow_alloc(void)
if (!stats)
goto err;

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

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]);
@@ -1194,9 +1195,26 @@ int ovs_flow_init(void)
BUILD_BUG_ON(__alignof__(struct sw_flow_key) % __alignof__(long));
BUILD_BUG_ON(sizeof(struct sw_flow_key) % sizeof(long));

+ /* Simply embedding 'struct cpumask' in 'struct sw_flow'
+ * consumes memory unnecessarily large. Cpumask is an bitmap
+ * of CONFIG_NR_CPUS bits, which is hardcoded in .config
+ * and default value can be 8192, in this case is 1024 bytes.
+ * It drops ovs_flow_alloc performance and cost memory.
+ * We should use actual CPU count instead of hardcoded value.
+ *
+ * To address this, 'cpu_used_mask' is redefined to pointer
+ * and append a cpumask_size() after 'stat' to hold the memory
+ * for struct cpumask.
+ *
+ * cpumask APIs like cpumask_next and cpumask_set_cpu are defined
+ * to never access bits beyond cpu count, as such above change is
+ * safe even though the actual memory provided is smaller than
+ * sizeof(struct cpumask)
+ */
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