From:   Eddy Tao <taoyuan_eddy@hotmail.com>
To:     netdev@vger.kernel.org
Cc:     Eddy Tao <taoyuan_eddy@hotmail.com>,
        Pravin B Shelar <pshelar@ovn.org>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>, dev@openvswitch.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH net-next v8 1/1] net: openvswitch: reduce cpu_used_mask memory
Date:   Sun,  5 Feb 2023 09:35:37 +0800
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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>
---
 V7 -> V8: add blanc space after colon in subject line
 V6 -> V7: initialize cpu_used_mask after stats_last_writer
 V5 -> V6: add tab to align the wrapped cpumask_set_cpu call
 V4 -> V5: fix max-line-length warning
 V3 -> V4: no change, sorry, my bad
 V2 -> V3: add 'net-next' in prefix
           fix max-line-length warning
           remove the comment
 V1 -> V2: make comment imperitive
           remove unnecessary parentheses

 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