10 files changed, 61 insertions, 6 deletions

diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index 10742902146f..53cea9bcb14c 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -516,6 +516,19 @@ tcp_wmem - vector of 3 INTEGERs: min, default, max
         this value is ignored.
         Default: between 64K and 4MB, depending on RAM size.
 
+tcp_notsent_lowat - UNSIGNED INTEGER
+        A TCP socket can control the amount of unsent bytes in its write queue,
+        thanks to TCP_NOTSENT_LOWAT socket option. poll()/select()/epoll()
+        reports POLLOUT events if the amount of unsent bytes is below a per
+        socket value, and if the write queue is not full. sendmsg() will
+        also not add new buffers if the limit is hit.
+
+        This global variable controls the amount of unsent data for
+        sockets not using TCP_NOTSENT_LOWAT. For these sockets, a change
+        to the global variable has immediate effect.
+
+        Default: UINT_MAX (0xFFFFFFFF)
+
 tcp_workaround_signed_windows - BOOLEAN
         If set, assume no receipt of a window scaling option means the
         remote TCP is broken and treats the window as a signed quantity.
diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 472120b4fac5..9640803a17a7 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -238,6 +238,7 @@ struct tcp_sock {
 
         u32     rcv_wnd;        /* Current receiver window              */
         u32     write_seq;      /* Tail(+1) of data held in tcp send buffer */
+        u32     notsent_lowat;  /* TCP_NOTSENT_LOWAT */
         u32     pushed_seq;     /* Last pushed seq, required to talk to windows */
         u32     lost_out;       /* Lost packets                 */
         u32     sacked_out;     /* SACK'd packets                       */
diff --git a/include/net/sock.h b/include/net/sock.h
index d0b5fdee50a2..b9f2b095b1ab 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -746,11 +746,6 @@ static inline int sk_stream_wspace(const struct sock *sk)
 
 extern void sk_stream_write_space(struct sock *sk);
 
-static inline bool sk_stream_memory_free(const struct sock *sk)
-{
-        return sk->sk_wmem_queued < sk->sk_sndbuf;
-}
-
 /* OOB backlog add */
 static inline void __sk_add_backlog(struct sock *sk, struct sk_buff *skb)
 {
@@ -950,6 +945,7 @@ struct proto {
         unsigned int            inuse_idx;
 #endif
 
+        bool                    (*stream_memory_free)(const struct sock *sk);
         /* Memory pressure */
         void                    (*enter_memory_pressure)(struct sock *sk);
         atomic_long_t           *memory_allocated;      /* Current allocated memory. */
@@ -1088,11 +1084,22 @@ static inline struct cg_proto *parent_cg_proto(struct proto *proto,
 }
 #endif
 
+static inline bool sk_stream_memory_free(const struct sock *sk)
+{
+        if (sk->sk_wmem_queued >= sk->sk_sndbuf)
+                return false;
+
+        return sk->sk_prot->stream_memory_free ?
+                sk->sk_prot->stream_memory_free(sk) : true;
+}
+
 static inline bool sk_stream_is_writeable(const struct sock *sk)
 {
-        return sk_stream_wspace(sk) >= sk_stream_min_wspace(sk);
+        return sk_stream_wspace(sk) >= sk_stream_min_wspace(sk) &&
+               sk_stream_memory_free(sk);
 }
 
+
 static inline bool sk_has_memory_pressure(const struct sock *sk)
 {
         return sk->sk_prot->memory_pressure != NULL;
diff --git a/include/net/tcp.h b/include/net/tcp.h
index c5868471abae..18fc999dae3c 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -284,6 +284,7 @@ extern int sysctl_tcp_thin_dupack;
 extern int sysctl_tcp_early_retrans;
 extern int sysctl_tcp_limit_output_bytes;
 extern int sysctl_tcp_challenge_ack_limit;
+extern unsigned int sysctl_tcp_notsent_lowat;
 
 extern atomic_long_t tcp_memory_allocated;
 extern struct percpu_counter tcp_sockets_allocated;
@@ -1539,6 +1540,19 @@ extern int tcp_gro_complete(struct sk_buff *skb);
 extern void __tcp_v4_send_check(struct sk_buff *skb, __be32 saddr,
                                 __be32 daddr);
 
+static inline u32 tcp_notsent_lowat(const struct tcp_sock *tp)
+{
+        return tp->notsent_lowat ?: sysctl_tcp_notsent_lowat;
+}
+
+static inline bool tcp_stream_memory_free(const struct sock *sk)
+{
+        const struct tcp_sock *tp = tcp_sk(sk);
+        u32 notsent_bytes = tp->write_seq - tp->snd_nxt;
+
+        return notsent_bytes < tcp_notsent_lowat(tp);
+}
+
 #ifdef CONFIG_PROC_FS
 extern int tcp4_proc_init(void);
 extern void tcp4_proc_exit(void);
diff --git a/include/uapi/linux/tcp.h b/include/uapi/linux/tcp.h
index 8d776ebc4829..377f1e59411d 100644
--- a/include/uapi/linux/tcp.h
+++ b/include/uapi/linux/tcp.h
@@ -111,6 +111,7 @@ enum {
 #define TCP_REPAIR_OPTIONS      22
 #define TCP_FASTOPEN            23      /* Enable FastOpen on listeners */
 #define TCP_TIMESTAMP           24
+#define TCP_NOTSENT_LOWAT       25      /* limit number of unsent bytes in write queue */
 
 struct tcp_repair_opt {
         __u32   opt_code;
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index b2c123c44d69..69ed203802da 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -555,6 +555,13 @@ static struct ctl_table ipv4_table[] = {
                 .extra1         = &one,
         },
         {
+                .procname       = "tcp_notsent_lowat",
+                .data           = &sysctl_tcp_notsent_lowat,
+                .maxlen         = sizeof(sysctl_tcp_notsent_lowat),
+                .mode           = 0644,
+                .proc_handler   = proc_dointvec,
+        },
+        {
                 .procname       = "tcp_rmem",
                 .data           = &sysctl_tcp_rmem,
                 .maxlen         = sizeof(sysctl_tcp_rmem),
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 5eca9060bb8e..c27e81392398 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2631,6 +2631,10 @@ static int do_tcp_setsockopt(struct sock *sk, int level,
                 else
                         tp->tsoffset = val - tcp_time_stamp;
                 break;
+        case TCP_NOTSENT_LOWAT:
+                tp->notsent_lowat = val;
+                sk->sk_write_space(sk);
+                break;
         default:
                 err = -ENOPROTOOPT;
                 break;
@@ -2847,6 +2851,9 @@ static int do_tcp_getsockopt(struct sock *sk, int level,
         case TCP_TIMESTAMP:
                 val = tcp_time_stamp + tp->tsoffset;
                 break;
+        case TCP_NOTSENT_LOWAT:
+                val = tp->notsent_lowat;
+                break;
         default:
                 return -ENOPROTOOPT;
         }
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 2e3f129df0eb..2a5d5c469d17 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -2800,6 +2800,7 @@ struct proto tcp_prot = {
         .unhash                 = inet_unhash,
         .get_port               = inet_csk_get_port,
         .enter_memory_pressure  = tcp_enter_memory_pressure,
+        .stream_memory_free     = tcp_stream_memory_free,
         .sockets_allocated      = &tcp_sockets_allocated,
         .orphan_count           = &tcp_orphan_count,
         .memory_allocated       = &tcp_memory_allocated,
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 92fde8d1aa82..884efff5b531 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -65,6 +65,9 @@ int sysctl_tcp_base_mss __read_mostly = TCP_BASE_MSS;
 /* By default, RFC2861 behavior.  */
 int sysctl_tcp_slow_start_after_idle __read_mostly = 1;
 
+unsigned int sysctl_tcp_notsent_lowat __read_mostly = UINT_MAX;
+EXPORT_SYMBOL(sysctl_tcp_notsent_lowat);
+
 static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
                            int push_one, gfp_t gfp);
 
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 80fe69ef2188..b792e870686b 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1924,6 +1924,7 @@ struct proto tcpv6_prot = {
         .unhash                 = inet_unhash,
         .get_port               = inet_csk_get_port,
         .enter_memory_pressure  = tcp_enter_memory_pressure,
+        .stream_memory_free     = tcp_stream_memory_free,
         .sockets_allocated      = &tcp_sockets_allocated,
         .memory_allocated       = &tcp_memory_allocated,
         .memory_pressure        = &tcp_memory_pressure,