Merge branch 'tcp-add-three-static-keys'

Eric Dumazet says:

====================
tcp: add three static keys

Recent addition of per TCP socket rx/tx cache brought
regressions for some workloads, as reported by Feng Tang.

It seems better to make them opt-in, before we adopt better
heuristics.

The last patch adds high_order_alloc_disable sysctl
to ask TCP sendmsg() to exclusively use order-0 allocations,
as mm layer has specific optimizations.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/ip-sysctl.txt

@@ -772,6 +772,14 @@ tcp_challenge_ack_limit - INTEGER
 	in RFC 5961 (Improving TCP's Robustness to Blind In-Window Attacks)
 	Default: 100
 
+tcp_rx_skb_cache - BOOLEAN
+	Controls a per TCP socket cache of one skb, that might help
+	performance of some workloads. This might be dangerous
+	on systems with a lot of TCP sockets, since it increases
+	memory usage.
+
+	Default: 0 (disabled)
+
 UDP variables:
 
 udp_l3mdev_accept - BOOLEAN

include/linux/bpf.h

@@ -600,7 +600,6 @@ void bpf_map_area_free(void *base);
 void bpf_map_init_from_attr(struct bpf_map *map, union bpf_attr *attr);
 
 extern int sysctl_unprivileged_bpf_disabled;
-extern int sysctl_bpf_stats_enabled;
 
 int bpf_map_new_fd(struct bpf_map *map, int flags);
 int bpf_prog_new_fd(struct bpf_prog *prog);

include/linux/sysctl.h

@@ -63,6 +63,9 @@ extern int proc_doulongvec_ms_jiffies_minmax(struct ctl_table *table, int,
 				      void __user *, size_t *, loff_t *);
 extern int proc_do_large_bitmap(struct ctl_table *, int,
 				void __user *, size_t *, loff_t *);
+extern int proc_do_static_key(struct ctl_table *table, int write,
+			      void __user *buffer, size_t *lenp,
+			      loff_t *ppos);
 
 /*
  * Register a set of sysctl names by calling register_sysctl_table

include/net/sock.h

@@ -1463,12 +1463,14 @@ static inline void sk_mem_uncharge(struct sock *sk, int size)
 		__sk_mem_reclaim(sk, 1 << 20);
 }
 
+DECLARE_STATIC_KEY_FALSE(tcp_tx_skb_cache_key);
 static inline void sk_wmem_free_skb(struct sock *sk, struct sk_buff *skb)
 {
 	sock_set_flag(sk, SOCK_QUEUE_SHRUNK);
 	sk->sk_wmem_queued -= skb->truesize;
 	sk_mem_uncharge(sk, skb->truesize);
-	if (!sk->sk_tx_skb_cache && !skb_cloned(skb)) {
+	if (static_branch_unlikely(&tcp_tx_skb_cache_key) &&
+	    !sk->sk_tx_skb_cache && !skb_cloned(skb)) {
 		skb_zcopy_clear(skb, true);
 		sk->sk_tx_skb_cache = skb;
 		return;
@@ -2433,13 +2435,11 @@ static inline void skb_setup_tx_timestamp(struct sk_buff *skb, __u16 tsflags)
  * This routine must be called with interrupts disabled or with the socket
  * locked so that the sk_buff queue operation is ok.
 */
+DECLARE_STATIC_KEY_FALSE(tcp_rx_skb_cache_key);
 static inline void sk_eat_skb(struct sock *sk, struct sk_buff *skb)
 {
 	__skb_unlink(skb, &sk->sk_receive_queue);
-	if (
-#ifdef CONFIG_RPS
-	    !static_branch_unlikely(&rps_needed) &&
-#endif
+	if (static_branch_unlikely(&tcp_rx_skb_cache_key) &&
 	    !sk->sk_rx_skb_cache) {
 		sk->sk_rx_skb_cache = skb;
 		skb_orphan(skb);
@@ -2534,6 +2534,8 @@ extern int sysctl_optmem_max;
 extern __u32 sysctl_wmem_default;
 extern __u32 sysctl_rmem_default;
 
+DECLARE_STATIC_KEY_FALSE(net_high_order_alloc_disable_key);
+
 static inline int sk_get_wmem0(const struct sock *sk, const struct proto *proto)
 {
 	/* Does this proto have per netns sysctl_wmem ? */

kernel/bpf/core.c

@@ -2097,7 +2097,6 @@ int __weak skb_copy_bits(const struct sk_buff *skb, int offset, void *to,
 
 DEFINE_STATIC_KEY_FALSE(bpf_stats_enabled_key);
 EXPORT_SYMBOL(bpf_stats_enabled_key);
-int sysctl_bpf_stats_enabled __read_mostly;
 
 /* All definitions of tracepoints related to BPF. */
 #define CREATE_TRACE_POINTS

kernel/sysctl.c

@@ -230,11 +230,6 @@ static int proc_dostring_coredump(struct ctl_table *table, int write,
 #endif
 static int proc_dopipe_max_size(struct ctl_table *table, int write,
 		void __user *buffer, size_t *lenp, loff_t *ppos);
-#ifdef CONFIG_BPF_SYSCALL
-static int proc_dointvec_minmax_bpf_stats(struct ctl_table *table, int write,
-					  void __user *buffer, size_t *lenp,
-					  loff_t *ppos);
-#endif
 
 #ifdef CONFIG_MAGIC_SYSRQ
 /* Note: sysrq code uses its own private copy */
@@ -1253,12 +1248,10 @@ static struct ctl_table kern_table[] = {
 	},
 	{
 		.procname	= "bpf_stats_enabled",
-		.data		= &sysctl_bpf_stats_enabled,
-		.maxlen		= sizeof(sysctl_bpf_stats_enabled),
+		.data		= &bpf_stats_enabled_key.key,
+		.maxlen		= sizeof(bpf_stats_enabled_key),
 		.mode		= 0644,
-		.proc_handler	= proc_dointvec_minmax_bpf_stats,
-		.extra1		= &zero,
-		.extra2		= &one,
+		.proc_handler	= proc_do_static_key,
 	},
 #endif
 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)
@@ -3374,26 +3367,35 @@ int proc_do_large_bitmap(struct ctl_table *table, int write,
 
 #endif /* CONFIG_PROC_SYSCTL */
 
-#if defined(CONFIG_BPF_SYSCALL) && defined(CONFIG_SYSCTL)
-static int proc_dointvec_minmax_bpf_stats(struct ctl_table *table, int write,
-					  void __user *buffer, size_t *lenp,
-					  loff_t *ppos)
+#if defined(CONFIG_SYSCTL)
+int proc_do_static_key(struct ctl_table *table, int write,
+		       void __user *buffer, size_t *lenp,
+		       loff_t *ppos)
 {
-	int ret, bpf_stats = *(int *)table->data;
-	struct ctl_table tmp = *table;
+	struct static_key *key = (struct static_key *)table->data;
+	static DEFINE_MUTEX(static_key_mutex);
+	int val, ret;
+	struct ctl_table tmp = {
+		.data   = &val,
+		.maxlen = sizeof(val),
+		.mode   = table->mode,
+		.extra1 = &zero,
+		.extra2 = &one,
+	};
 
 	if (write && !capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
-	tmp.data = &bpf_stats;
+	mutex_lock(&static_key_mutex);
+	val = static_key_enabled(key);
 	ret = proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos);
 	if (write && !ret) {
-		*(int *)table->data = bpf_stats;
-		if (bpf_stats)
-			static_branch_enable(&bpf_stats_enabled_key);
+		if (val)
+			static_key_enable(key);
 		else
-			static_branch_disable(&bpf_stats_enabled_key);
+			static_key_disable(key);
 	}
+	mutex_unlock(&static_key_mutex);
 	return ret;
 }
 #endif

net/core/sock.c

@@ -2320,6 +2320,7 @@ static void sk_leave_memory_pressure(struct sock *sk)
 
 /* On 32bit arches, an skb frag is limited to 2^15 */
 #define SKB_FRAG_PAGE_ORDER	get_order(32768)
+DEFINE_STATIC_KEY_FALSE(net_high_order_alloc_disable_key);
 
 /**
  * skb_page_frag_refill - check that a page_frag contains enough room
@@ -2344,7 +2345,8 @@ bool skb_page_frag_refill(unsigned int sz, struct page_frag *pfrag, gfp_t gfp)
 	}
 
 	pfrag->offset = 0;
-	if (SKB_FRAG_PAGE_ORDER) {
+	if (SKB_FRAG_PAGE_ORDER &&
+	    !static_branch_unlikely(&net_high_order_alloc_disable_key)) {
 		/* Avoid direct reclaim but allow kswapd to wake */
 		pfrag->page = alloc_pages((gfp & ~__GFP_DIRECT_RECLAIM) |
 					  __GFP_COMP | __GFP_NOWARN |

net/core/sysctl_net_core.c

@@ -562,6 +562,13 @@ static struct ctl_table net_core_table[] = {
 		.extra1		= &zero,
 		.extra2		= &two,
 	},
+	{
+		.procname	= "high_order_alloc_disable",
+		.data		= &net_high_order_alloc_disable_key.key,
+		.maxlen         = sizeof(net_high_order_alloc_disable_key),
+		.mode		= 0644,
+		.proc_handler	= proc_do_static_key,
+	},
 	{ }
 };
 

net/ipv4/sysctl_net_ipv4.c

@@ -51,6 +51,11 @@ static int comp_sack_nr_max = 255;
 static u32 u32_max_div_HZ = UINT_MAX / HZ;
 static int one_day_secs = 24 * 3600;
 
+DEFINE_STATIC_KEY_FALSE(tcp_rx_skb_cache_key);
+EXPORT_SYMBOL(tcp_rx_skb_cache_key);
+
+DEFINE_STATIC_KEY_FALSE(tcp_tx_skb_cache_key);
+
 /* obsolete */
 static int sysctl_tcp_low_latency __read_mostly;
 
@@ -559,6 +564,18 @@ static struct ctl_table ipv4_table[] = {
 		.extra1		= &sysctl_fib_sync_mem_min,
 		.extra2		= &sysctl_fib_sync_mem_max,
 	},
+	{
+		.procname	= "tcp_rx_skb_cache",
+		.data		= &tcp_rx_skb_cache_key.key,
+		.mode		= 0644,
+		.proc_handler	= proc_do_static_key,
+	},
+	{
+		.procname	= "tcp_tx_skb_cache",
+		.data		= &tcp_tx_skb_cache_key.key,
+		.mode		= 0644,
+		.proc_handler	= proc_do_static_key,
+	},
 	{ }
 };