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Date: Wed, 1 Feb 2023 13:09:20 +0100
From: Jiri Pirko <jiri@...nulli.us>
To: taoyuan_eddy@...mail.com
Cc: dev@...nvswitch.org, Pravin B Shelar <pshelar@....org>,
"David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: openvswitch: reduce cpu_used_mask memory consumption
Tue, Jan 31, 2023 at 02:58:22PM CET, taoyuan_eddy@...mail.com wrote:
>From: eddytaoyuan <taoyuan_eddy@...mail.com>
>
>struct cpumask cpu_used_mask is directly embedded in struct sw_flow
>however, its size is hardcoded to CONFIG_NR_CPUS bits, which
>can be as large as 8192 by default, it cost memory and slows down
>ovs_flow_alloc, this fix used actual CPU number instead
>
>Signed-off-by: eddytaoyuan <taoyuan_eddy@...mail.com>
Hmm, I guess that the name should be rather "Dddy Taoyuan" ? Please fix,
also in your "From:" header and preferably email client.
>---
> net/openvswitch/flow.c | 6 +++---
> net/openvswitch/flow.h | 2 +-
> net/openvswitch/flow_table.c | 25 ++++++++++++++++++++++---
> 3 files changed, 26 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..c0fdff73272f 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 +1195,27 @@ 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 including 'struct cpumask' in 'struct sw_flow'
>+ * consumes memory unnecessarily large.
>+ * The reason is that compilation option CONFIG_NR_CPUS(default 8192)
>+ * decides the value of NR_CPUS, which in turn decides size of
>+ * 'struct cpumask', which means 1024 bytes are needed for the cpumask
>+ * It affects ovs_flow_alloc performance as well as memory footprint.
>+ * 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 actual memory
>+ * of struct cpumask
>+ *
>+ * cpumask APIs like cpumask_next and cpumask_set_cpu have been defined
>+ * to never access bits beyond cpu count by design, thus above change is
>+ * safe even though the actual memory provided is smaller than
>+ * sizeof(struct cpumask)
I don't understand the reason to have this comment in the code. From
what I see, this should be moved to the patch description. Of course
with changing the mood to imperation when you say the codebase what to
do.
>+ */
> 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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