[PATCH net-next 2/3] tcp: adjust sndbuf according to sk_reserved_mem

[Wei Wang <weiwan@google.com>]

If user sets SO_RESERVE_MEM socket option, in order to fully utilize the
reserved memory in memory pressure state on the tx path, we modify the
logic in sk_stream_moderate_sndbuf() to set sk_sndbuf according to
available reserved memory, instead of MIN_SOCK_SNDBUF, and adjust it
when new data is acked.

Signed-off-by: Wei Wang <weiwan@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com> 
---
 include/net/sock.h   |  1 +
 net/ipv4/tcp_input.c | 14 ++++++++++++--
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/include/net/sock.h b/include/net/sock.h
index b0df2d3843fd..e6ad628adcd2 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -2388,6 +2388,7 @@ 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/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 141e85e6422b..a7611256f235 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5381,7 +5381,7 @@ static int tcp_prune_queue(struct sock *sk)
 	return -1;
 }
 
-static bool tcp_should_expand_sndbuf(const struct sock *sk)
+static bool tcp_should_expand_sndbuf(struct sock *sk)
 {
 	const struct tcp_sock *tp = tcp_sk(sk);
 
@@ -5392,8 +5392,18 @@ static bool tcp_should_expand_sndbuf(const struct sock *sk)
 		return false;
 
 	/* If we are under global TCP memory pressure, do not expand.  */
-	if (tcp_under_memory_pressure(sk))
+	if (tcp_under_memory_pressure(sk)) {
+		int unused_mem = sk_unused_reserved_mem(sk);
+
+		/* Adjust sndbuf according to reserved mem. But make sure
+		 * it never goes below SOCK_MIN_SNDBUF.
+		 * See sk_stream_moderate_sndbuf() for more details.
+		 */
+		if (unused_mem > SOCK_MIN_SNDBUF)
+			WRITE_ONCE(sk->sk_sndbuf, unused_mem);
+
 		return false;
+	}
 
 	/* If we are under soft global TCP memory pressure, do not expand.  */
 	if (sk_memory_allocated(sk) >= sk_prot_mem_limits(sk, 0))
-- 
2.33.0.685.g46640cef36-goog