Merge branch 'lwip/acceptmbox_config' into 'master'

change(lwip): Added macro to configure TCP accept mailbox size

See merge request espressif/esp-idf!27276

components/esp_wifi/src/wifi_init.c

@@ -190,6 +190,7 @@ static void esp_wifi_config_info(void)
 #endif
 
 #ifdef CONFIG_ESP_NETIF_TCPIP_LWIP
+    ESP_LOGI(TAG, "accept mbox: %d", CONFIG_LWIP_TCP_ACCEPTMBOX_SIZE);
     ESP_LOGI(TAG, "tcpip mbox: %d", CONFIG_LWIP_TCPIP_RECVMBOX_SIZE);
     ESP_LOGI(TAG, "udp mbox: %d", CONFIG_LWIP_UDP_RECVMBOX_SIZE);
     ESP_LOGI(TAG, "tcp mbox: %d", CONFIG_LWIP_TCP_RECVMBOX_SIZE);

components/lwip/Kconfig

@@ -665,6 +665,20 @@ menu "LWIP"
                 mail box is full, the LWIP drops the packets. So generally we need to make sure the TCP
                 receive mail box is big enough to avoid packet drop between LWIP core and application.
 
+        config LWIP_TCP_ACCEPTMBOX_SIZE
+            int "Default TCP accept mail box size"
+            default 6
+            range 1 64 if !LWIP_WND_SCALE
+            range 1 255 if LWIP_WND_SCALE
+            help
+                Set TCP accept mail box size. Generally bigger value means supporting larger backlogs
+                but more memory. The recommended value is 6, but applications can set it to a lower value
+                if listening servers are meant to have a smaller backlog.
+
+                TCP accept mail box is a per socket mail box, when the application listens for connections
+                with a given listening TCP socket. If the mailbox is full, LWIP will send a RST packet and
+                the client will fail to connect.
+
         config LWIP_TCP_QUEUE_OOSEQ
             bool "Queue incoming out-of-order segments"
             default y

components/lwip/port/include/lwipopts.h

@@ -849,7 +849,7 @@ static inline uint32_t timeout_from_offered(uint32_t lease, uint32_t min)
  * The queue size value itself is platform-dependent, but is passed to
  * sys_mbox_new() when the acceptmbox is created.
  */
-#define DEFAULT_ACCEPTMBOX_SIZE         6
+#define DEFAULT_ACCEPTMBOX_SIZE         CONFIG_LWIP_TCP_ACCEPTMBOX_SIZE
 
 /**
  * DEFAULT_THREAD_STACKSIZE: The stack size used by any other lwIP thread.

docs/en/api-guides/coexist.rst

@@ -246,6 +246,7 @@ Setting Coexistence Compile-time Options
       #) :ref:`CONFIG_LWIP_TCP_SND_BUF_DEFAULT`: reduce the default TX buffer size for TCP sockets.
       #) :ref:`CONFIG_LWIP_TCP_WND_DEFAULT`:  reduce the default size of the RX window for TCP sockets.
       #) :ref:`CONFIG_LWIP_TCP_RECVMBOX_SIZE`: reduce the size of the TCP receive mailbox.
+      #) :ref:`CONFIG_LWIP_TCP_ACCEPTMBOX_SIZE`: reduce the size of the TCP accept mailbox.
       #) :ref:`CONFIG_LWIP_UDP_RECVMBOX_SIZE`: reduce the size of the UDP receive mailbox.
       #) :ref:`CONFIG_LWIP_TCPIP_RECVMBOX_SIZE`: reduce the size of TCPIP task receive mailbox.
 

docs/en/api-guides/lwip.rst

@@ -503,6 +503,7 @@ Most lwIP RAM usage is on-demand, as RAM is allocated from the heap as needed. T
 
 - Reducing :ref:`CONFIG_LWIP_MAX_SOCKETS` reduces the maximum number of sockets in the system. This also causes TCP sockets in the ``WAIT_CLOSE`` state to be closed and recycled more rapidly when needed to open a new socket, further reducing peak RAM usage.
 - Reducing :ref:`CONFIG_LWIP_TCPIP_RECVMBOX_SIZE`, :ref:`CONFIG_LWIP_TCP_RECVMBOX_SIZE` and :ref:`CONFIG_LWIP_UDP_RECVMBOX_SIZE` reduce RAM usage at the expense of throughput, depending on usage.
+- Reducing :ref:`CONFIG_LWIP_TCP_ACCEPTMBOX_SIZE` reduce RAM usage by limiting concurrent accepted connections.
 - Reducing :ref:`CONFIG_LWIP_TCP_MSL` and :ref:`CONFIG_LWIP_TCP_FIN_WAIT_TIMEOUT` reduces the maximum segment lifetime in the system. This also causes TCP sockets in the ``TIME_WAIT`` and ``FIN_WAIT_2`` states to be closed and recycled more rapidly.
 - Disabling :ref:`CONFIG_LWIP_IPV6` can save about 39 KB for firmware size and 2 KB RAM when the system is powered up and 7 KB RAM when the TCP/IP stack is running. If there is no requirement for supporting IPV6, it can be disabled to save flash and RAM footprint.
 - Disabling :ref:`CONFIG_LWIP_IPV4` can save about 26 KB of firmware size and 600 B RAM on power up and 6 KB RAM when the TCP/IP stack is running. If the local network supports IPv6-only configuration, IPv4 can be disabled to save flash and RAM footprint.