2023-02-03 08:41:01

by 缘 陶

Subject: [PATCH net-next v4 1/1] net:openvswitch:reduce cpu_used_mask memory

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

cpumask 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 <[email protected]>
---
net/openvswitch/flow.c | 8 +++++---
net/openvswitch/flow.h | 2 +-
net/openvswitch/flow_table.c | 8 +++++---
3 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/net/openvswitch/flow.c b/net/openvswitch/flow.c
index e20d1a973417..0109a5f86f6a 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 +135,8 @@ 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 +160,8 @@ 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..dc6a174c3194 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]);
@@ -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

2023-02-03 08:58:56

by Jiri Pirko

Subject: Re: [PATCH net-next v4 1/1] net:openvswitch:reduce cpu_used_mask memory

Fri, Feb 03, 2023 at 09:40:36AM CET, [email protected] wrote:
>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
>
>cpumask 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 <[email protected]>

Reviewed-by: Jiri Pirko <[email protected]>