Merge branch 'SO_RESEVED_MEM'

Wei Wang says:

====================
net: add new socket option SO_RESERVE_MEM

This patch series introduces a new socket option SO_RESERVE_MEM.
This socket option provides a mechanism for users to reserve a certain
amount of memory for the socket to use. When this option is set, kernel
charges the user specified amount of memory to memcg, as well as
sk_forward_alloc. This amount of memory is not reclaimable and is
available in sk_forward_alloc for this socket.
With this socket option set, the networking stack spends less cycles
doing forward alloc and reclaim, which should lead to better system
performance, with the cost of an amount of pre-allocated and
unreclaimable memory, even under memory pressure.
With a tcp_stream test with 10 flows running on a simulated 100ms RTT
link, I can see the cycles spent in __sk_mem_raise_allocated() dropping
by ~0.02%. Not a whole lot, since we already have logic in
sk_mem_uncharge() to only reclaim 1MB when sk_forward_alloc has more
than 2MB free space. But on a system suffering memory pressure
constently, the savings should be more.

The first patch is the implementation of this socket option. The
following 2 patches change the tcp stack to make use of this reserved
memory when under memory pressure. This makes the tcp stack behavior
more flexible when under memory pressure, and provides a way for user to
control the distribution of the memory among its sockets.
With a TCP connection on a simulated 100ms RTT link, the default
throughput under memory pressure is ~500Kbps. With SO_RESERVE_MEM set to
100KB, the throughput under memory pressure goes up to ~3.5Mbps.

Change since v2:
- Added description for new field added in struct sock in patch 1
Change since v1:
- Added performance stats in cover letter and rebased
====================

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

3 files changed, 53 insertions, 5 deletions

diff --git a/include/net/sock.h b/include/net/sock.h
index 879980de3dcd..c3af696258fe 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -269,6 +269,7 @@ struct bpf_local_storage;
   *	@sk_omem_alloc: "o" is "option" or "other"
   *	@sk_wmem_queued: persistent queue size
   *	@sk_forward_alloc: space allocated forward
+  *	@sk_reserved_mem: space reserved and non-reclaimable for the socket
   *	@sk_napi_id: id of the last napi context to receive data for sk
   *	@sk_ll_usec: usecs to busypoll when there is no data
   *	@sk_allocation: allocation mode
@@ -409,6 +410,7 @@ struct sock {
 #define sk_rmem_alloc sk_backlog.rmem_alloc
 
 	int			sk_forward_alloc;
+	u32			sk_reserved_mem;
 #ifdef CONFIG_NET_RX_BUSY_POLL
 	unsigned int		sk_ll_usec;
 	/* ===== mostly read cache line ===== */
@@ -1511,20 +1513,49 @@ sk_rmem_schedule(struct sock *sk, struct sk_buff *skb, int size)
 		skb_pfmemalloc(skb);
 }
 
+static inline int sk_unused_reserved_mem(const struct sock *sk)
+{
+	int unused_mem;
+
+	if (likely(!sk->sk_reserved_mem))
+		return 0;
+
+	unused_mem = sk->sk_reserved_mem - sk->sk_wmem_queued -
+			atomic_read(&sk->sk_rmem_alloc);
+
+	return unused_mem > 0 ? unused_mem : 0;
+}
+
 static inline void sk_mem_reclaim(struct sock *sk)
 {
+	int reclaimable;
+
 	if (!sk_has_account(sk))
 		return;
-	if (sk->sk_forward_alloc >= SK_MEM_QUANTUM)
-		__sk_mem_reclaim(sk, sk->sk_forward_alloc);
+
+	reclaimable = sk->sk_forward_alloc - sk_unused_reserved_mem(sk);
+
+	if (reclaimable >= SK_MEM_QUANTUM)
+		__sk_mem_reclaim(sk, reclaimable);
+}
+
+static inline void sk_mem_reclaim_final(struct sock *sk)
+{
+	sk->sk_reserved_mem = 0;
+	sk_mem_reclaim(sk);
 }
 
 static inline void sk_mem_reclaim_partial(struct sock *sk)
 {
+	int reclaimable;
+
 	if (!sk_has_account(sk))
 		return;
-	if (sk->sk_forward_alloc > SK_MEM_QUANTUM)
-		__sk_mem_reclaim(sk, sk->sk_forward_alloc - 1);
+
+	reclaimable = sk->sk_forward_alloc - sk_unused_reserved_mem(sk);
+
+	if (reclaimable > SK_MEM_QUANTUM)
+		__sk_mem_reclaim(sk, reclaimable - 1);
 }
 
 static inline void sk_mem_charge(struct sock *sk, int size)
@@ -1536,9 +1567,12 @@ static inline void sk_mem_charge(struct sock *sk, int size)
 
 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()
@@ -1547,7 +1581,7 @@ static inline void sk_mem_uncharge(struct sock *sk, int size)
 	 * If we reach 2 MBytes, reclaim 1 MBytes right now, there is
 	 * no need to hold that much forward allocation anyway.
 	 */
-	if (unlikely(sk->sk_forward_alloc >= 1 << 21))
+	if (unlikely(reclaimable >= 1 << 21))
 		__sk_mem_reclaim(sk, 1 << 20);
 }
 
@@ -2344,6 +2378,7 @@ static inline void sk_stream_moderate_sndbuf(struct sock *sk)
 		return;
 
 	val = min(sk->sk_sndbuf, sk->sk_wmem_queued >> 1);
+	val = max_t(u32, val, sk_unused_reserved_mem(sk));
 
 	WRITE_ONCE(sk->sk_sndbuf, max_t(u32, val, SOCK_MIN_SNDBUF));
 }
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 32cf6c01f403..4c2898ac6569 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1421,6 +1421,17 @@ static inline int tcp_full_space(const struct sock *sk)
 	return tcp_win_from_space(sk, READ_ONCE(sk->sk_rcvbuf));
 }
 
+static inline void tcp_adjust_rcv_ssthresh(struct sock *sk)
+{
+	int unused_mem = sk_unused_reserved_mem(sk);
+	struct tcp_sock *tp = tcp_sk(sk);
+
+	tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss);
+	if (unused_mem)
+		tp->rcv_ssthresh = max_t(u32, tp->rcv_ssthresh,
+					 tcp_win_from_space(sk, unused_mem));
+}
+
 void tcp_cleanup_rbuf(struct sock *sk, int copied);
 
 /* We provision sk_rcvbuf around 200% of sk_rcvlowat.
diff --git a/include/uapi/asm-generic/socket.h b/include/uapi/asm-generic/socket.h
index 1f0a2b4864e4..c77a1313b3b0 100644
--- a/include/uapi/asm-generic/socket.h
+++ b/include/uapi/asm-generic/socket.h
@@ -126,6 +126,8 @@
 
 #define SO_BUF_LOCK		72
 
+#define SO_RESERVE_MEM		73
+
 #if !defined(__KERNEL__)
 
 #if __BITS_PER_LONG == 64 || (defined(__x86_64__) && defined(__ILP32__))