diff --git a/src/node/net/p2p_connection.ml b/src/node/net/p2p_connection.ml
index 8c00b04b5..35c521cdf 100644
--- a/src/node/net/p2p_connection.ml
+++ b/src/node/net/p2p_connection.ml
@@ -10,8 +10,6 @@
 (* TODO encode/encrypt before to push into the writer pipe. *)
 (* TODO patch Sodium.Box to avoid allocation of the encrypted buffer.*)
 (* TODO patch Data_encoding for continuation-based binary writer/reader. *)
-(* TODO use queue bound by memory size of its elements, not by the
-        number of elements. *)
 (* TODO test `close ~wait:true`. *)
 (* TODO nothing in welcoming message proves that the incoming peer is
         the owner of the public key... only the first message will
@@ -218,7 +216,7 @@ module Reader = struct
     canceler: Canceler.t ;
     conn: connection ;
     encoding: 'msg Data_encoding.t ;
-    messages: 'msg tzresult Lwt_pipe.t ;
+    messages: (int * 'msg) tzresult Lwt_pipe.t ;
     mutable worker: unit Lwt.t ;
   }
 
@@ -229,13 +227,15 @@ module Reader = struct
     Lwt_unix.yield () >>= fun () ->
     Lwt_utils.protect ~canceler:st.canceler begin fun () ->
       Crypto.read_chunk st.conn.fd st.conn.cryptobox_data >>=? fun buf ->
-      read_message st buf
+      let size = 6 * (Sys.word_size / 8) + MBytes.length buf in
+      read_message st buf >>|? fun msg ->
+      size, msg
     end >>= function
-    | Ok None ->
+    | Ok (_, None) ->
         Lwt_pipe.push st.messages (Error [Decoding_error]) >>= fun () ->
         worker_loop st
-    | Ok (Some msg) ->
-        Lwt_pipe.push st.messages (Ok msg) >>= fun () ->
+    | Ok (size, Some msg) ->
+        Lwt_pipe.push st.messages (Ok (size, msg)) >>= fun () ->
         worker_loop st
     | Error [Lwt_utils.Canceled | Exn Lwt_pipe.Closed] ->
         Lwt.return_unit
@@ -245,6 +245,11 @@ module Reader = struct
         Lwt.return_unit
 
   let run ?size conn encoding canceler =
+    let compute_size = function
+      | Ok (size, _) -> (Sys.word_size / 8) * 11 + size
+      | Error _ -> 0 (* we push Error only when we close the socket,
+                        we don't fear memory leaks in that case... *) in
+    let size = map_option size ~f:(fun max -> (max, compute_size)) in
     let st =
       { canceler ; conn ; encoding ;
         messages = Lwt_pipe.create ?size () ;
@@ -301,6 +306,13 @@ module Writer = struct
         Lwt.return_unit
 
   let run ?size conn encoding canceler =
+    let compute_size = function
+      | msg, None ->
+          10 * (Sys.word_size / 8) + Data_encoding.Binary.length encoding msg
+      | msg, Some _ ->
+          18 * (Sys.word_size / 8) + Data_encoding.Binary.length encoding msg
+    in
+    let size = map_option size ~f:(fun max -> max, compute_size) in
     let st =
       { canceler ; conn ; encoding ;
         messages = Lwt_pipe.create ?size () ;
@@ -367,10 +379,6 @@ let catch_closed_pipe f =
     | exn -> fail (Exn exn)
   end
 
-let is_writable { writer } =
-  not (Lwt_pipe.is_full writer.messages)
-let wait_writable { writer } =
-  Lwt_pipe.not_full writer.messages
 let write { writer } msg =
   catch_closed_pipe begin fun () ->
     Lwt_pipe.push writer.messages (msg, None) >>= return
diff --git a/src/node/net/p2p_connection.mli b/src/node/net/p2p_connection.mli
index 890cc6c34..4a4cc8b58 100644
--- a/src/node/net/p2p_connection.mli
+++ b/src/node/net/p2p_connection.mli
@@ -71,14 +71,6 @@ val accept:
 
 (** {2 Output functions} *)
 
-val is_writable: 'msg t -> bool
-(** [is_writable conn] is [true] iff [conn] internal write queue is
-    not full. *)
-
-val wait_writable: 'msg t -> unit Lwt.t
-(** (Cancelable) [wait_writable conn] returns when [conn]'s internal
-    write queue becomes writable (i.e. not full). *)
-
 val write: 'msg t -> 'msg -> unit tzresult Lwt.t
 (** [write conn msg] returns when [msg] has successfully been added to
     [conn]'s internal write queue or fails with a corresponding
@@ -103,12 +95,12 @@ val wait_readable: 'msg t -> unit tzresult Lwt.t
 (** (Cancelable) [wait_readable conn] returns when [conn]'s internal
     read queue becomes readable (i.e. not empty). *)
 
-val read: 'msg t -> 'msg tzresult Lwt.t
+val read: 'msg t -> (int * 'msg) tzresult Lwt.t
 (** [read conn msg] returns when [msg] has successfully been popped
     from [conn]'s internal read queue or fails with a corresponding
     error. *)
 
-val read_now: 'msg t -> 'msg tzresult option
+val read_now: 'msg t -> (int * 'msg) tzresult option
 (** [read_now conn msg] is [Some msg] if [conn]'s internal read queue
     is not empty, [None] if it is empty, or fails with a correponding
     error otherwise. *)
diff --git a/src/node/net/p2p_connection_pool.ml b/src/node/net/p2p_connection_pool.ml
index 53826a029..23d2eb09e 100644
--- a/src/node/net/p2p_connection_pool.ml
+++ b/src/node/net/p2p_connection_pool.ml
@@ -65,7 +65,7 @@ module Answerer = struct
   type 'msg callback = {
     bootstrap: unit -> Point.t list Lwt.t ;
     advertise: Point.t list -> unit Lwt.t ;
-    message: 'msg -> unit Lwt.t ;
+    message: int -> 'msg -> unit Lwt.t ;
   }
 
   type 'msg t = {
@@ -80,7 +80,7 @@ module Answerer = struct
     Lwt_utils.protect ~canceler:st.canceler begin fun () ->
       P2p_connection.read st.conn
     end >>= function
-    | Ok Bootstrap -> begin
+    | Ok (_, Bootstrap) -> begin
         st.callback.bootstrap () >>= function
         | [] ->
             worker_loop st
@@ -93,13 +93,13 @@ module Answerer = struct
                 Canceler.cancel st.canceler >>= fun () ->
                 Lwt.return_unit
       end
-    | Ok (Advertise points) ->
+    | Ok (_, Advertise points) ->
         st.callback.advertise points >>= fun () ->
         worker_loop st
-    | Ok (Message msg) ->
-        st.callback.message msg >>= fun () ->
+    | Ok (size, Message msg) ->
+        st.callback.message size msg >>= fun () ->
         worker_loop st
-    | Ok Disconnect | Error [P2p_io_scheduler.Connection_closed] ->
+    | Ok (_, Disconnect) | Error [P2p_io_scheduler.Connection_closed] ->
         Canceler.cancel st.canceler >>= fun () ->
         Lwt.return_unit
     | Error [Lwt_utils.Canceled] ->
@@ -181,7 +181,7 @@ and events = {
 
 and ('msg, 'meta) connection = {
   canceler : Canceler.t ;
-  messages : 'msg Lwt_pipe.t ;
+  messages : (int * 'msg) Lwt_pipe.t ;
   conn : 'msg Message.t P2p_connection.t ;
   gid_info : (('msg, 'meta) connection, 'meta) Gid_info.t ;
   point_info : ('msg, 'meta) connection Point_info.t option ;
@@ -248,10 +248,13 @@ let active_connections pool = Gid.Table.length pool.connected_gids
 let create_connection pool conn id_point pi gi =
   let gid = Gid_info.gid gi in
   let canceler = Canceler.create () in
-  let messages =
-    Lwt_pipe.create ?size:pool.config.incoming_app_message_queue_size () in
+  let size =
+    map_option pool.config.incoming_app_message_queue_size
+      ~f:(fun qs -> qs, fun (size, _) -> (Sys.word_size / 8) * 11 + size) in
+  let messages = Lwt_pipe.create ?size () in
   let callback =
-    { Answerer.message = Lwt_pipe.push messages ;
+    { Answerer.message =
+        (fun size msg -> Lwt_pipe.push messages (size, msg)) ;
       advertise = register_new_points pool gid ;
       bootstrap = list_known_points pool gid ;
     } in
@@ -471,7 +474,7 @@ let accept pool fd point =
 
 let read { messages } =
   Lwt.catch
-    (fun () -> Lwt_pipe.pop messages >>= return)
+    (fun () -> Lwt_pipe.pop messages >>= fun ( _, msg) -> return msg)
     (fun _ (* Closed *) -> fail P2p_io_scheduler.Connection_closed)
 
 let is_readable { messages } =
diff --git a/src/node/net/p2p_io_scheduler.ml b/src/node/net/p2p_io_scheduler.ml
index 14c00b357..7b3fcd164 100644
--- a/src/node/net/p2p_io_scheduler.ml
+++ b/src/node/net/p2p_io_scheduler.ml
@@ -315,6 +315,13 @@ let create
 
 exception Closed
 
+let read_size = function
+  | Ok buf -> (Sys.word_size / 8) * 8 + MBytes.length buf
+  | Error _ -> 0 (* we push Error only when we close the socket,
+                    we don't fear memory leaks in that case... *)
+
+let write_size mbytes = (Sys.word_size / 8) * 6 + MBytes.length mbytes
+
 let register =
   let cpt = ref 0 in
   fun st conn ->
@@ -324,8 +331,12 @@ let register =
   end else begin
     let id = incr cpt; !cpt in
     let canceler = Canceler.create () in
-    let read_queue = Lwt_pipe.create ?size:st.read_queue_size ()
-    and write_queue = Lwt_pipe.create ?size:st.write_queue_size () in
+    let read_size =
+      map_option st.read_queue_size ~f:(fun v -> v, read_size) in
+    let write_size =
+      map_option st.write_queue_size ~f:(fun v -> v, write_size) in
+    let read_queue = Lwt_pipe.create ?size:read_size () in
+    let write_queue = Lwt_pipe.create ?size:write_size () in
     let read_conn =
       ReadScheduler.create_connection
         st.read_scheduler (conn, st.read_buffer_size) read_queue canceler id
diff --git a/src/node/net/p2p_io_scheduler.mli b/src/node/net/p2p_io_scheduler.mli
index 9e5d20139..f5641ff35 100644
--- a/src/node/net/p2p_io_scheduler.mli
+++ b/src/node/net/p2p_io_scheduler.mli
@@ -41,7 +41,7 @@ val create:
 (** [create ~max_upload_speed ~max_download_speed ~read_queue_size
     ~write_queue_size ()] is an IO scheduler with specified (global)
     max upload (resp. download) speed, and specified read
-    (resp. write) queue sizes for connections. *)
+    (resp. write) queue sizes (in bytes) for connections. *)
 
 val register: t -> Lwt_unix.file_descr -> connection
 (** [register sched fd] is a [connection] managed by [sched]. *)
diff --git a/src/utils/lwt_pipe.ml b/src/utils/lwt_pipe.ml
index e86293fb4..0fede0225 100644
--- a/src/utils/lwt_pipe.ml
+++ b/src/utils/lwt_pipe.ml
@@ -10,25 +10,30 @@
 open Lwt.Infix
 
 type 'a t =
-  { queue : 'a Queue.t ;
-    size : int option ;
+  { queue : (int * 'a) Queue.t ;
+    mutable current_size : int ;
+    max_size : int ;
+    compute_size : ('a -> int) ;
     mutable closed : bool ;
     mutable push_waiter : (unit Lwt.t * unit Lwt.u) option ;
     mutable pop_waiter : (unit Lwt.t * unit Lwt.u) option ;
     empty: unit Lwt_condition.t ;
-    full: unit Lwt_condition.t ;
-    not_full : unit Lwt_condition.t ;
   }
 
 let create ?size () =
+  let max_size, compute_size =
+    match size with
+    | None -> max_int, (fun _ -> 0)
+    | Some (max_size, compute_size) ->
+        max_size, (fun e -> 4 * (Sys.word_size / 8) + compute_size e) in
   { queue = Queue.create () ;
-    size ;
+    current_size = 0 ;
+    max_size ;
+    compute_size ;
     closed = false ;
     push_waiter = None ;
     pop_waiter = None ;
     empty = Lwt_condition.create () ;
-    full = Lwt_condition.create () ;
-    not_full = Lwt_condition.create () ;
   }
 
 let notify_push q =
@@ -61,49 +66,40 @@ let wait_pop q =
       q.pop_waiter <- Some (waiter, wakener) ;
       Lwt.protected waiter
 
-let available_space { size } len =
-  match size with
-  | None -> true
-  | Some size -> len < size
-
 let length { queue } = Queue.length queue
 let is_empty { queue } = Queue.is_empty queue
-let is_full ({ queue } as q) = not (available_space q (Queue.length queue))
 
 let rec empty q =
   if is_empty q
   then Lwt.return_unit
   else (Lwt_condition.wait q.empty >>= fun () -> empty q)
-let rec full q =
-  if is_full q
-  then Lwt.return_unit
-  else (Lwt_condition.wait q.full >>= fun () -> full q)
-let rec not_full q =
-  if not (is_empty q)
-  then Lwt.return_unit
-  else (Lwt_condition.wait q.not_full >>= fun () -> not_full q)
 
 exception Closed
 
-let rec push ({ closed ; queue ; full } as q) elt =
-  let len = Queue.length queue in
-  if closed then Lwt.fail Closed
-  else if available_space q len then begin
-    Queue.push elt queue ;
+let rec push ({ closed ; queue ; current_size ;
+                max_size ; compute_size} as q) elt =
+  let elt_size = compute_size elt in
+  if closed then
+    Lwt.fail Closed
+  else if current_size + elt_size < max_size || Queue.is_empty queue then begin
+    Queue.push (elt_size, elt) queue ;
+    q.current_size <- current_size + elt_size ;
     notify_push q ;
-    (if not (available_space q (len + 1)) then Lwt_condition.signal full ());
     Lwt.return_unit
   end else
     wait_pop q >>= fun () ->
     push q elt
 
-let rec push_now ({ closed ; queue ; full } as q) elt =
+let rec push_now ({ closed ; queue ; compute_size ;
+                    current_size ; max_size
+                  } as q) elt =
   if closed then raise Closed ;
-  let len = Queue.length queue in
-  available_space q len && begin
-    Queue.push elt queue ;
+  let elt_size = compute_size elt in
+  (current_size + elt_size < max_size || Queue.is_empty queue)
+  && begin
+    Queue.push (elt_size, elt) queue ;
+    q.current_size <- current_size + elt_size ;
     notify_push q ;
-    (if not (available_space q (len + 1)) then Lwt_condition.signal full ()) ;
     true
   end
 
@@ -112,27 +108,11 @@ exception Full
 let push_now_exn q elt =
   if not (push_now q elt) then raise Full
 
-let rec pop_all ({ closed ; queue ; empty ; not_full } as q) =
-  let was_full = is_full q in
+let rec pop ({ closed ; queue ; empty ; current_size } as q) =
   if not (Queue.is_empty queue) then
-    let queue_copy = Queue.copy queue in
-    Queue.clear queue;
+    let (elt_size, elt) = Queue.pop queue in
     notify_pop q ;
-    (if was_full then Lwt_condition.signal not_full ());
-    Lwt_condition.signal empty ();
-    Lwt.return queue_copy
-  else if closed then
-    Lwt.fail Closed
-  else
-    wait_push q >>= fun () ->
-    pop_all q
-
-let rec pop ({ closed ; queue ; empty ; not_full } as q) =
-  let was_full = is_full q in
-  if not (Queue.is_empty queue) then
-    let elt = Queue.pop queue in
-    notify_pop q ;
-    (if was_full then Lwt_condition.signal not_full ());
+    q.current_size <- current_size - elt_size ;
     (if Queue.length queue = 0 then Lwt_condition.signal empty ());
     Lwt.return elt
   else if closed then
@@ -143,7 +123,7 @@ let rec pop ({ closed ; queue ; empty ; not_full } as q) =
 
 let rec peek ({ closed ; queue } as q) =
   if not (Queue.is_empty queue) then
-    let elt = Queue.peek queue in
+    let (_elt_size, elt) = Queue.peek queue in
     Lwt.return elt
   else if closed then
     Lwt.fail Closed
@@ -153,28 +133,15 @@ let rec peek ({ closed ; queue } as q) =
 
 exception Empty
 
-let pop_now_exn ({ closed ; queue ; empty ; not_full } as q) =
-  let was_full = is_full q in
+let pop_now_exn ({ closed ; queue ; empty ; current_size } as q) =
   if Queue.is_empty queue then
     (if closed then raise Closed else raise Empty) ;
-  let elt = Queue.pop queue in
-  (if was_full then Lwt_condition.signal not_full ());
+  let (elt_size, elt) = Queue.pop queue in
   (if Queue.length queue = 0 then Lwt_condition.signal empty ());
+  q.current_size <- current_size - elt_size ;
   notify_pop q ;
   elt
 
-let pop_all_now ({ closed ; queue ; empty ; not_full } as q) =
-  let was_empty = is_empty q in
-  let was_full = is_full q in
-  if Queue.is_empty queue then
-    (if closed then raise Closed else raise Empty) ;
-  let queue_copy = Queue.copy queue in
-  Queue.clear queue ;
-  (if was_full then Lwt_condition.signal not_full ());
-  (if not was_empty then Lwt_condition.signal empty ());
-  notify_pop q ;
-  queue_copy
-
 let pop_now q =
   match pop_now_exn q with
   | exception Empty -> None
@@ -195,7 +162,6 @@ let close q =
     q.closed <- true ;
     notify_push q ;
     notify_pop q ;
-    Lwt_condition.broadcast_exn q.full Closed ;
   end
 
 let rec iter q ~f =
diff --git a/src/utils/lwt_pipe.mli b/src/utils/lwt_pipe.mli
index 8b282f36a..cbeb995a5 100644
--- a/src/utils/lwt_pipe.mli
+++ b/src/utils/lwt_pipe.mli
@@ -14,18 +14,15 @@
 type 'a t
 (** Type of queues holding values of type ['a]. *)
 
-val create : ?size:int -> unit -> 'a t
-(** [create ~size] is an empty queue that can hold max [size]
-    elements. *)
+val create : ?size:(int * ('a -> int)) -> unit -> 'a t
+(** [create ~size:(max_size, compute_size)] is an empty queue that can
+    hold max [size] bytes of data, using [compute_size] to compute the
+    size of a datum. *)
 
 val push : 'a t -> 'a -> unit Lwt.t
 (** [push q v] is a thread that blocks while [q] contains more
     than [size] elements, then adds [v] at the end of [q]. *)
 
-val pop_all : 'a t -> 'a Queue.t Lwt.t
-(** [pop' q] is a thread that returns all elements in [q] or waits
-    till there is at least one element in [q]. *)
-
 val pop : 'a t -> 'a Lwt.t
 (** [pop q] is a thread that blocks while [q] is empty, then
     removes and returns the first element in [q]. *)
@@ -48,10 +45,6 @@ val push_now_exn : 'a t -> 'a -> unit
 (** [push_now q v] adds [v] at the ends of [q] immediately or
     raise [Full] if [q] is currently full. *)
 
-val pop_all_now : 'a t -> 'a Queue.t
-(** [pop_all_now q] is a copy of [q]'s internal queue, that may be
-    empty. *)
-
 val pop_now : 'a t -> 'a option
 (** [pop_now q] maybe removes and returns the first element in [q] if
     [q] contains at least one element. *)
@@ -68,18 +61,9 @@ val length : 'a t -> int
 val is_empty : 'a t -> bool
 (** [is_empty q] is [true] if [q] is empty, [false] otherwise. *)
 
-val is_full : 'a t -> bool
-(** [is_full q] is [true] if [q] is full, [false] otherwise. *)
-
 val empty : 'a t -> unit Lwt.t
 (** [empty q] returns when [q] becomes empty. *)
 
-val full : 'a t -> unit Lwt.t
-(** [full q] returns when [q] becomes full. *)
-
-val not_full : 'a t -> unit Lwt.t
-(** [not_full q] returns when [q] stop being full. *)
-
 val iter : 'a t -> f:('a -> unit Lwt.t) -> unit Lwt.t
 (** [iter q ~f] pops all elements of [q] and applies [f] on them. *)
 
diff --git a/test/test_p2p_connection.ml b/test/test_p2p_connection.ml
index c0d6dbf19..bf041db8a 100644
--- a/test/test_p2p_connection.ml
+++ b/test/test_p2p_connection.ml
@@ -161,14 +161,14 @@ let client addr port =
   (* let's exchange a simple message. *)
   connect sched addr port id2 >>=? fun auth_fd ->
   P2p_connection.accept auth_fd bytes_encoding >>=? fun conn ->
-  P2p_connection.read conn >>=? fun msg ->
+  P2p_connection.read conn >>=? fun (msg_size, msg) ->
   assert (MBytes.compare simple_msg msg = 0) ;
   P2p_connection.close conn >>= fun _stat ->
   lwt_log_notice "Simple OK" >>= fun () ->
   (* let's detect a closed connection on `read`. *)
   connect sched addr port id2 >>=? fun auth_fd ->
   P2p_connection.accept auth_fd bytes_encoding >>=? fun conn ->
-  P2p_connection.read conn >>=? fun msg ->
+  P2p_connection.read conn >>=? fun (msg_size, msg) ->
   assert (MBytes.compare simple_msg msg = 0) ;
   P2p_connection.read conn >>= fun msg ->
   assert (is_connection_closed msg) ;
diff --git a/test/test_p2p_io_scheduler.ml b/test/test_p2p_io_scheduler.ml
index 0db147c3d..2319964a7 100644
--- a/test/test_p2p_io_scheduler.ml
+++ b/test/test_p2p_io_scheduler.ml
@@ -170,8 +170,8 @@ let max_download_speed = ref None
 let max_upload_speed = ref None
 
 let read_buffer_size = ref (1 lsl 14)
-let read_queue_size = ref (Some 1)
-let write_queue_size = ref (Some 1)
+let read_queue_size = ref (Some (1 lsl 14))
+let write_queue_size = ref (Some (1 lsl 14))
 
 let delay = ref 60.
 let clients = ref 8