Patch for nginx originaly by cloudflare. Read https://habrahabr.ru/post/282465/ , Ported to nginx-1.12.

nginx-1.12_send_minimum_rate.patch

Index: nginx-1.12.0/src/core/ngx_connection.c
===================================================================
--- nginx-1.12.0.orig/src/core/ngx_connection.c	2017-04-15 04:39:30.043542084 +0300
+++ nginx-1.12.0/src/core/ngx_connection.c	2017-04-15 04:39:29.885545744 +0300
@@ -1402,3 +1402,60 @@
 
     return NGX_ERROR;
 }
+
+
+/*
+ * When a socket is idle, determines if the kernel is draining its buffer
+ * faster than minimum_rate. Avoids false negatives by allowing sufficient
+ * time to pass (currently 1 second) before recording the current send rate.
+ * Used to avoid closing an active connection whose buffers are so large
+ * relative to throughput that we stop sending data for long periods of time.
+ */
+ngx_flag_t
+ngx_connection_sending_above_rate(
+    ngx_connection_t *c, size_t minimum_rate)
+{
+    ssize_t     new_unacknowledged_bytes, bytes_sent;
+    ngx_msec_t  t1, time_elapsed;
+    ngx_time_t *tp;
+
+    if (minimum_rate == 0) {
+        return 0;
+    }
+
+    tp = ngx_timeofday();
+    t1 = (ngx_msec_t) (tp->sec * 1000 + tp->msec);
+    time_elapsed = t1 - c->last_send_rate_time;
+
+    if (time_elapsed < 1000) {
+        /*
+         * Need more time to get an accurate rate.
+         * Defends against spurious wakeups when used in the timeout handler
+         */
+        return 1;
+    }
+
+    new_unacknowledged_bytes = ngx_tcp_unacknowledged_bytes(c->fd);
+    bytes_sent = c->socket_unacknowledged_bytes - new_unacknowledged_bytes;
+
+    c->socket_unacknowledged_bytes = new_unacknowledged_bytes;
+    c->last_send_rate_time = t1;
+
+    if (bytes_sent < 0) {
+        /* buffer grew */
+        return 1;
+    }
+
+    if ((size_t)bytes_sent >= (time_elapsed * minimum_rate) / 1000) {
+        return 1;
+    }
+
+    return 0;
+}
+
+
+void
+ngx_connection_reset_send_rate(ngx_connection_t *c)
+{
+    c->socket_unacknowledged_bytes = 0;
+}
Index: nginx-1.12.0/src/core/ngx_connection.h
===================================================================
--- nginx-1.12.0.orig/src/core/ngx_connection.h	2017-04-15 04:39:30.043542084 +0300
+++ nginx-1.12.0/src/core/ngx_connection.h	2017-04-15 04:39:29.885545744 +0300
@@ -189,6 +189,9 @@
 #if (NGX_THREADS || NGX_COMPAT)
     ngx_thread_task_t  *sendfile_task;
 #endif
+
+    ssize_t             socket_unacknowledged_bytes;
+    ngx_msec_t          last_send_rate_time;
 };
 
 
@@ -221,4 +224,8 @@
 
 void ngx_reusable_connection(ngx_connection_t *c, ngx_uint_t reusable);
 
+ngx_flag_t ngx_connection_sending_above_rate(ngx_connection_t *c,
+    size_t minimum_rate);
+void ngx_connection_reset_send_rate(ngx_connection_t *c);
+
 #endif /* _NGX_CONNECTION_H_INCLUDED_ */
Index: nginx-1.12.0/src/http/ngx_http_core_module.c
===================================================================
--- nginx-1.12.0.orig/src/http/ngx_http_core_module.c	2017-04-15 04:39:30.043542084 +0300
+++ nginx-1.12.0/src/http/ngx_http_core_module.c	2017-04-15 04:39:29.886545721 +0300
@@ -763,6 +763,13 @@
 
 #endif
 
+    { ngx_string("send_minimum_rate"),
+      NGX_HTTP_MAIN_CONF|NGX_HTTP_SRV_CONF|NGX_HTTP_LOC_CONF|NGX_CONF_TAKE1,
+      ngx_conf_set_size_slot,
+      NGX_HTTP_LOC_CONF_OFFSET,
+      offsetof(ngx_http_core_loc_conf_t, send_minimum_rate),
+      NULL },
+
       ngx_null_command
 };
 
@@ -3581,6 +3588,7 @@
     clcf->tcp_nopush = NGX_CONF_UNSET;
     clcf->tcp_nodelay = NGX_CONF_UNSET;
     clcf->send_timeout = NGX_CONF_UNSET_MSEC;
+    clcf->send_minimum_rate = NGX_CONF_UNSET_SIZE;
     clcf->send_lowat = NGX_CONF_UNSET_SIZE;
     clcf->postpone_output = NGX_CONF_UNSET_SIZE;
     clcf->limit_rate = NGX_CONF_UNSET_SIZE;
@@ -3807,6 +3815,8 @@
     ngx_conf_merge_value(conf->tcp_nodelay, prev->tcp_nodelay, 1);
 
     ngx_conf_merge_msec_value(conf->send_timeout, prev->send_timeout, 60000);
+    ngx_conf_merge_size_value(conf->send_minimum_rate, prev->send_minimum_rate,
+                              0);
     ngx_conf_merge_size_value(conf->send_lowat, prev->send_lowat, 0);
     ngx_conf_merge_size_value(conf->postpone_output, prev->postpone_output,
                               1460);
Index: nginx-1.12.0/src/http/ngx_http_core_module.h
===================================================================
--- nginx-1.12.0.orig/src/http/ngx_http_core_module.h	2017-04-15 04:39:30.043542084 +0300
+++ nginx-1.12.0/src/http/ngx_http_core_module.h	2017-04-15 04:39:29.887545698 +0300
@@ -362,6 +362,7 @@
     size_t        limit_rate_after;        /* limit_rate_after */
     size_t        sendfile_max_chunk;      /* sendfile_max_chunk */
     size_t        read_ahead;              /* read_ahead */
+    size_t        send_minimum_rate;       /* send_minimum_rate */
 
     ngx_msec_t    client_body_timeout;     /* client_body_timeout */
     ngx_msec_t    send_timeout;            /* send_timeout */
Index: nginx-1.12.0/src/http/ngx_http_request.c
===================================================================
--- nginx-1.12.0.orig/src/http/ngx_http_request.c	2017-04-15 04:39:30.043542084 +0300
+++ nginx-1.12.0/src/http/ngx_http_request.c	2017-04-15 04:39:29.887545698 +0300
@@ -2626,6 +2626,13 @@
     clcf = ngx_http_get_module_loc_conf(r->main, ngx_http_core_module);
 
     if (wev->timedout) {
+        if (ngx_connection_sending_above_rate(c, clcf->send_minimum_rate)) {
+            wev->timedout = 0;
+            if (!wev->delayed) {
+                ngx_add_timer(wev, clcf->send_timeout);
+            }
+            return;
+        }
         ngx_log_error(NGX_LOG_INFO, c->log, NGX_ETIMEDOUT,
                       "client timed out");
         c->timedout = 1;
@@ -2634,6 +2641,8 @@
         return;
     }
 
+    ngx_connection_reset_send_rate(c);
+
     if (wev->delayed || r->aio) {
         ngx_log_debug0(NGX_LOG_DEBUG_HTTP, wev->log, 0,
                        "http writer delayed");
Index: nginx-1.12.0/src/http/ngx_http_upstream.c
===================================================================
--- nginx-1.12.0.orig/src/http/ngx_http_upstream.c	2017-04-15 04:39:30.043542084 +0300
+++ nginx-1.12.0/src/http/ngx_http_upstream.c	2017-04-15 04:39:29.889545652 +0300
@@ -3295,13 +3295,22 @@
     downstream = c;
     upstream = u->peer.connection;
 
+    clcf = ngx_http_get_module_loc_conf(r, ngx_http_core_module);
+
     if (downstream->write->timedout) {
-        c->timedout = 1;
-        ngx_connection_error(c, NGX_ETIMEDOUT, "client timed out");
-        ngx_http_upstream_finalize_request(r, u, NGX_HTTP_REQUEST_TIME_OUT);
-        return;
+        if (ngx_connection_sending_above_rate(c, clcf->send_minimum_rate)) {
+            downstream->write->timedout = 0;
+
+        } else {
+            c->timedout = 1;
+            ngx_connection_error(c, NGX_ETIMEDOUT, "client timed out");
+            ngx_http_upstream_finalize_request(r, u, NGX_HTTP_REQUEST_TIME_OUT);
+            return;
+        }
     }
 
+    ngx_connection_reset_send_rate(c);
+
     if (upstream->read->timedout || upstream->write->timedout) {
         ngx_connection_error(c, NGX_ETIMEDOUT, "upstream timed out");
         ngx_http_upstream_finalize_request(r, u, NGX_HTTP_GATEWAY_TIME_OUT);
@@ -3404,8 +3413,6 @@
         return;
     }
 
-    clcf = ngx_http_get_module_loc_conf(r, ngx_http_core_module);
-
     if (ngx_handle_write_event(upstream->write, u->conf->send_lowat)
         != NGX_OK)
     {
@@ -3459,6 +3466,7 @@
     ngx_event_t          *wev;
     ngx_connection_t     *c;
     ngx_http_upstream_t  *u;
+    ngx_http_core_loc_conf_t  *clcf;
 
     c = r->connection;
     u = r->upstream;
@@ -3470,12 +3478,21 @@
     c->log->action = "sending to client";
 
     if (wev->timedout) {
-        c->timedout = 1;
-        ngx_connection_error(c, NGX_ETIMEDOUT, "client timed out");
-        ngx_http_upstream_finalize_request(r, u, NGX_HTTP_REQUEST_TIME_OUT);
-        return;
+        clcf = ngx_http_get_module_loc_conf(r, ngx_http_core_module);
+
+        if (ngx_connection_sending_above_rate(c, clcf->send_minimum_rate)) {
+            wev->timedout = 0;
+
+        } else {
+            c->timedout = 1;
+            ngx_connection_error(c, NGX_ETIMEDOUT, "client timed out");
+            ngx_http_upstream_finalize_request(r, u, NGX_HTTP_REQUEST_TIME_OUT);
+            return;
+        }
     }
 
+    ngx_connection_reset_send_rate(c);
+
     ngx_http_upstream_process_non_buffered_request(r, 1);
 }
 
@@ -3785,6 +3802,7 @@
     ngx_connection_t     *c;
     ngx_event_pipe_t     *p;
     ngx_http_upstream_t  *u;
+    ngx_http_core_loc_conf_t  *clcf;
 
     c = r->connection;
     u = r->upstream;
@@ -3801,7 +3819,18 @@
 #endif
 
     if (wev->timedout) {
+        clcf = ngx_http_get_module_loc_conf(r, ngx_http_core_module);
+
+        if (ngx_connection_sending_above_rate(c, clcf->send_minimum_rate)) {
+            wev->timedout = 0;
+            ngx_add_timer(wev, p->send_timeout);
 
+            if (ngx_handle_write_event(wev, p->send_lowat) != NGX_OK) {
+                ngx_http_upstream_finalize_request(r, u, NGX_ERROR);
+            }
+
+            return;
+        }
         p->downstream_error = 1;
         c->timedout = 1;
         ngx_connection_error(c, NGX_ETIMEDOUT, "client timed out");
@@ -3826,6 +3855,8 @@
         }
     }
 
+    ngx_connection_reset_send_rate(c);
+
     ngx_http_upstream_process_request(r, u);
 }
 
Index: nginx-1.12.0/src/os/unix/ngx_socket.c
===================================================================
--- nginx-1.12.0.orig/src/os/unix/ngx_socket.c	2017-04-15 04:39:30.043542084 +0300
+++ nginx-1.12.0/src/os/unix/ngx_socket.c	2017-04-15 04:39:29.889545652 +0300
@@ -114,3 +114,28 @@
 }
 
 #endif
+
+
+#if (NGX_LINUX)
+
+int
+ngx_tcp_unacknowledged_bytes(ngx_socket_t s)
+{
+    int  bs;
+
+    if (ioctl(s, TIOCOUTQ, &bs) == -1) {
+        return 0;
+    }
+
+    return bs;
+}
+
+#else
+
+int
+ngx_tcp_unacknowledged_bytes(ngx_socket_t s)
+{
+    return 0;
+}
+
+#endif
Index: nginx-1.12.0/src/os/unix/ngx_socket.h
===================================================================
--- nginx-1.12.0.orig/src/os/unix/ngx_socket.h	2017-04-15 04:39:30.043542084 +0300
+++ nginx-1.12.0/src/os/unix/ngx_socket.h	2017-04-15 04:39:29.889545652 +0300
@@ -40,6 +40,7 @@
 
 int ngx_tcp_nopush(ngx_socket_t s);
 int ngx_tcp_push(ngx_socket_t s);
+int ngx_tcp_unacknowledged_bytes(ngx_socket_t s);
 
 #if (NGX_LINUX)