net: keep sk->sk_forward_alloc as small as possible

Currently, tcp_memory_allocated can hit tcp_mem[] limits quite fast.

Each TCP socket can forward allocate up to 2 MB of memory, even after
flow became less active.

10,000 sockets can have reserved 20 GB of memory,
and we have no shrinker in place to reclaim that.

Instead of trying to reclaim the extra allocations in some places,
just keep sk->sk_forward_alloc values as small as possible.

This should not impact performance too much now we have per-cpu
reserves: Changes to tcp_memory_allocated should not be too frequent.

For sockets not using SO_RESERVE_MEM:
 - idle sockets (no packets in tx/rx queues) have zero forward alloc.
 - non idle sockets have a forward alloc smaller than one page.

Note:

 - Removal of SK_RECLAIM_CHUNK and SK_RECLAIM_THRESHOLD
   is left to MPTCP maintainers as a follow up.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

11 files changed, 7 insertions, 72 deletions

diff --git a/include/net/sock.h b/include/net/sock.h
index cf288f7e9019..0063e8410a4e 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1627,19 +1627,6 @@ static inline void sk_mem_reclaim_final(struct sock *sk)
 	sk_mem_reclaim(sk);
 }
 
-static inline void sk_mem_reclaim_partial(struct sock *sk)
-{
-	int reclaimable;
-
-	if (!sk_has_account(sk))
-		return;
-
-	reclaimable = sk->sk_forward_alloc - sk_unused_reserved_mem(sk);
-
-	if (reclaimable > (int)PAGE_SIZE)
-		__sk_mem_reclaim(sk, reclaimable - 1);
-}
-
 static inline void sk_mem_charge(struct sock *sk, int size)
 {
 	if (!sk_has_account(sk))
@@ -1647,29 +1634,17 @@ static inline void sk_mem_charge(struct sock *sk, int size)
 	sk->sk_forward_alloc -= size;
 }
 
-/* the following macros control memory reclaiming in sk_mem_uncharge()
+/* the following macros control memory reclaiming in mptcp_rmem_uncharge()
  */
 #define SK_RECLAIM_THRESHOLD	(1 << 21)
 #define SK_RECLAIM_CHUNK	(1 << 20)
 
 static inline void sk_mem_uncharge(struct sock *sk, int size)
 {
-	int reclaimable;
-
 	if (!sk_has_account(sk))
 		return;
 	sk->sk_forward_alloc += size;
-	reclaimable = sk->sk_forward_alloc - sk_unused_reserved_mem(sk);
-
-	/* Avoid a possible overflow.
-	 * TCP send queues can make this happen, if sk_mem_reclaim()
-	 * is not called and more than 2 GBytes are released at once.
-	 *
-	 * If we reach 2 MBytes, reclaim 1 MBytes right now, there is
-	 * no need to hold that much forward allocation anyway.
-	 */
-	if (unlikely(reclaimable >= SK_RECLAIM_THRESHOLD))
-		__sk_mem_reclaim(sk, SK_RECLAIM_CHUNK);
+	sk_mem_reclaim(sk);
 }
 
 /*
diff --git a/net/core/datagram.c b/net/core/datagram.c
index 50f4faeea76c..35791f86bd1a 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -320,7 +320,6 @@ EXPORT_SYMBOL(skb_recv_datagram);
 void skb_free_datagram(struct sock *sk, struct sk_buff *skb)
 {
 	consume_skb(skb);
-	sk_mem_reclaim_partial(sk);
 }
 EXPORT_SYMBOL(skb_free_datagram);
 
@@ -336,7 +335,6 @@ void __skb_free_datagram_locked(struct sock *sk, struct sk_buff *skb, int len)
 	slow = lock_sock_fast(sk);
 	sk_peek_offset_bwd(sk, len);
 	skb_orphan(skb);
-	sk_mem_reclaim_partial(sk);
 	unlock_sock_fast(sk, slow);
 
 	/* skb is now orphaned, can be freed outside of locked section */
@@ -396,7 +394,6 @@ int skb_kill_datagram(struct sock *sk, struct sk_buff *skb, unsigned int flags)
 				      NULL);
 
 	kfree_skb(skb);
-	sk_mem_reclaim_partial(sk);
 	return err;
 }
 EXPORT_SYMBOL(skb_kill_datagram);
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index e6bdf8e2c09a..14ebb4ec4a51 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -858,9 +858,6 @@ struct sk_buff *tcp_stream_alloc_skb(struct sock *sk, int size, gfp_t gfp,
 {
 	struct sk_buff *skb;
 
-	if (unlikely(tcp_under_memory_pressure(sk)))
-		sk_mem_reclaim_partial(sk);
-
 	skb = alloc_skb_fclone(size + MAX_TCP_HEADER, gfp);
 	if (likely(skb)) {
 		bool mem_scheduled;
@@ -2764,8 +2761,6 @@ void __tcp_close(struct sock *sk, long timeout)
 		__kfree_skb(skb);
 	}
 
-	sk_mem_reclaim(sk);
-
 	/* If socket has been already reset (e.g. in tcp_reset()) - kill it. */
 	if (sk->sk_state == TCP_CLOSE)
 		goto adjudge_to_death;
@@ -2873,7 +2868,6 @@ adjudge_to_death:
 		}
 	}
 	if (sk->sk_state != TCP_CLOSE) {
-		sk_mem_reclaim(sk);
 		if (tcp_check_oom(sk, 0)) {
 			tcp_set_state(sk, TCP_CLOSE);
 			tcp_send_active_reset(sk, GFP_ATOMIC);
@@ -2951,7 +2945,6 @@ void tcp_write_queue_purge(struct sock *sk)
 	}
 	tcp_rtx_queue_purge(sk);
 	INIT_LIST_HEAD(&tcp_sk(sk)->tsorted_sent_queue);
-	sk_mem_reclaim(sk);
 	tcp_clear_all_retrans_hints(tcp_sk(sk));
 	tcp_sk(sk)->packets_out = 0;
 	inet_csk(sk)->icsk_backoff = 0;
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 3fb117022558..fdc7beb81b68 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -805,7 +805,6 @@ static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb)
 			 * restart window, so that we send ACKs quickly.
 			 */
 			tcp_incr_quickack(sk, TCP_MAX_QUICKACKS);
-			sk_mem_reclaim(sk);
 		}
 	}
 	icsk->icsk_ack.lrcvtime = now;
@@ -4390,7 +4389,6 @@ void tcp_fin(struct sock *sk)
 	skb_rbtree_purge(&tp->out_of_order_queue);
 	if (tcp_is_sack(tp))
 		tcp_sack_reset(&tp->rx_opt);
-	sk_mem_reclaim(sk);
 
 	if (!sock_flag(sk, SOCK_DEAD)) {
 		sk->sk_state_change(sk);
@@ -5336,7 +5334,6 @@ static bool tcp_prune_ofo_queue(struct sock *sk)
 		tcp_drop_reason(sk, rb_to_skb(node),
 				SKB_DROP_REASON_TCP_OFO_QUEUE_PRUNE);
 		if (!prev || goal <= 0) {
-			sk_mem_reclaim(sk);
 			if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf &&
 			    !tcp_under_memory_pressure(sk))
 				break;
@@ -5383,7 +5380,6 @@ static int tcp_prune_queue(struct sock *sk)
 			     skb_peek(&sk->sk_receive_queue),
 			     NULL,
 			     tp->copied_seq, tp->rcv_nxt);
-	sk_mem_reclaim(sk);
 
 	if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
 		return 0;
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index 20cf4a98c69d..2208755e8efc 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -290,15 +290,13 @@ void tcp_delack_timer_handler(struct sock *sk)
 {
 	struct inet_connection_sock *icsk = inet_csk(sk);
 
-	sk_mem_reclaim_partial(sk);
-
 	if (((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) ||
 	    !(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
-		goto out;
+		return;
 
 	if (time_after(icsk->icsk_ack.timeout, jiffies)) {
 		sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout);
-		goto out;
+		return;
 	}
 	icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER;
 
@@ -317,10 +315,6 @@ void tcp_delack_timer_handler(struct sock *sk)
 		tcp_send_ack(sk);
 		__NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKS);
 	}
-
-out:
-	if (tcp_under_memory_pressure(sk))
-		sk_mem_reclaim(sk);
 }
 
 
@@ -600,11 +594,11 @@ void tcp_write_timer_handler(struct sock *sk)
 
 	if (((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) ||
 	    !icsk->icsk_pending)
-		goto out;
+		return;
 
 	if (time_after(icsk->icsk_timeout, jiffies)) {
 		sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout);
-		goto out;
+		return;
 	}
 
 	tcp_mstamp_refresh(tcp_sk(sk));
@@ -626,9 +620,6 @@ void tcp_write_timer_handler(struct sock *sk)
 		tcp_probe_timer(sk);
 		break;
 	}
-
-out:
-	sk_mem_reclaim(sk);
 }
 
 static void tcp_write_timer(struct timer_list *t)
@@ -743,8 +734,6 @@ static void tcp_keepalive_timer (struct timer_list *t)
 		elapsed = keepalive_time_when(tp) - elapsed;
 	}
 
-	sk_mem_reclaim(sk);
-
 resched:
 	inet_csk_reset_keepalive_timer (sk, elapsed);
 	goto out;
diff --git a/net/iucv/af_iucv.c b/net/iucv/af_iucv.c
index a0385ddbffcf..498a0c35b7bb 100644
--- a/net/iucv/af_iucv.c
+++ b/net/iucv/af_iucv.c
@@ -278,8 +278,6 @@ static void iucv_sock_destruct(struct sock *sk)
 	skb_queue_purge(&sk->sk_receive_queue);
 	skb_queue_purge(&sk->sk_error_queue);
 
-	sk_mem_reclaim(sk);
-
 	if (!sock_flag(sk, SOCK_DEAD)) {
 		pr_err("Attempt to release alive iucv socket %p\n", sk);
 		return;
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 9563124ac8af..e0fb9f96c45c 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -975,7 +975,7 @@ static void __mptcp_mem_reclaim_partial(struct sock *sk)
 	if (reclaimable > (int)PAGE_SIZE)
 		__mptcp_rmem_reclaim(sk, reclaimable - 1);
 
-	sk_mem_reclaim_partial(sk);
+	sk_mem_reclaim(sk);
 }
 
 static void mptcp_mem_reclaim_partial(struct sock *sk)
diff --git a/net/sctp/sm_statefuns.c b/net/sctp/sm_statefuns.c
index 52edee1322fc..f6ee7f4040c1 100644
--- a/net/sctp/sm_statefuns.c
+++ b/net/sctp/sm_statefuns.c
@@ -6590,8 +6590,6 @@ static int sctp_eat_data(const struct sctp_association *asoc,
 			pr_debug("%s: under pressure, reneging for tsn:%u\n",
 				 __func__, tsn);
 			deliver = SCTP_CMD_RENEGE;
-		} else {
-			sk_mem_reclaim(sk);
 		}
 	}
 
diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index 05174acd981a..171f1a35d205 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -1824,9 +1824,6 @@ static int sctp_sendmsg_to_asoc(struct sctp_association *asoc,
 	if (sctp_wspace(asoc) < (int)msg_len)
 		sctp_prsctp_prune(asoc, sinfo, msg_len - sctp_wspace(asoc));
 
-	if (sk_under_memory_pressure(sk))
-		sk_mem_reclaim(sk);
-
 	if (sctp_wspace(asoc) <= 0 || !sk_wmem_schedule(sk, msg_len)) {
 		timeo = sock_sndtimeo(sk, msg->msg_flags & MSG_DONTWAIT);
 		err = sctp_wait_for_sndbuf(asoc, &timeo, msg_len);
@@ -9195,8 +9192,6 @@ static int sctp_wait_for_sndbuf(struct sctp_association *asoc, long *timeo_p,
 			goto do_error;
 		if (signal_pending(current))
 			goto do_interrupted;
-		if (sk_under_memory_pressure(sk))
-			sk_mem_reclaim(sk);
 		if ((int)msg_len <= sctp_wspace(asoc) &&
 		    sk_wmem_schedule(sk, msg_len))
 			break;
diff --git a/net/sctp/stream_interleave.c b/net/sctp/stream_interleave.c
index 6b13f737ebf2..bb22b71df7a3 100644
--- a/net/sctp/stream_interleave.c
+++ b/net/sctp/stream_interleave.c
@@ -979,8 +979,6 @@ static void sctp_renege_events(struct sctp_ulpq *ulpq, struct sctp_chunk *chunk,
 
 	if (freed >= needed && sctp_ulpevent_idata(ulpq, chunk, gfp) <= 0)
 		sctp_intl_start_pd(ulpq, gfp);
-
-	sk_mem_reclaim(asoc->base.sk);
 }
 
 static void sctp_intl_stream_abort_pd(struct sctp_ulpq *ulpq, __u16 sid,
diff --git a/net/sctp/ulpqueue.c b/net/sctp/ulpqueue.c
index 407fed46931b..0a8510a0c5e6 100644
--- a/net/sctp/ulpqueue.c
+++ b/net/sctp/ulpqueue.c
@@ -1100,12 +1100,8 @@ void sctp_ulpq_renege(struct sctp_ulpq *ulpq, struct sctp_chunk *chunk,
 		else if (retval == 1)
 			sctp_ulpq_reasm_drain(ulpq);
 	}
-
-	sk_mem_reclaim(asoc->base.sk);
 }
 
-
-
 /* Notify the application if an association is aborted and in
  * partial delivery mode.  Send up any pending received messages.
  */