Re: [PATCH] unclamp tcp receive window if doing dynamic receive sizing

["David S. Miller" <davem@xxxxxxxxxx>]

As a followup I've put the following into my tree after discussing
some things with Stephen.  He will do some of his tests to make
sure this fixes things as it should.

# This is a BitKeeper generated diff -Nru style patch.
#
# ChangeSet
#   2004/06/10 21:53:15-07:00 davem@xxxxxxxxxxxxxxxxxx 
#   [TCP]: Receive buffer moderation fixes.
#   
#   1) Make window clamp follow receive buffer growth so it
#      does not limit window advertisements.  Noticed by John
#      Heffner and Stephen Hemminger.
#   2) Fix rcvmem calculation such that tcp_adv_win_scale is
#      taken into account.
# 
# net/ipv4/tcp_input.c
#   2004/06/10 21:52:43-07:00 davem@xxxxxxxxxxxxxxxxxx +9 -1
#   [TCP]: Receive buffer moderation fixes.
#   
#   1) Make window clamp follow receive buffer growth so it
#      does not limit window advertisements.  Noticed by John
#      Heffner and Stephen Hemminger.
#   
#   2) Fix rcvmem calculation such that tcp_adv_win_scale is
#      taken into account.
# 
diff -Nru a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
--- a/net/ipv4/tcp_input.c      2004-06-10 21:55:14 -07:00
+++ b/net/ipv4/tcp_input.c      2004-06-10 21:55:14 -07:00
@@ -463,6 +463,8 @@
                tp->rcvq_space.space = space;
 
                if (sysctl_tcp_moderate_rcvbuf) {
+                       int new_clamp = space;
+
                        /* Receive space grows, normalize in order to
                         * take into account packet headers and sk_buff
                         * structure overhead.
@@ -472,10 +474,16 @@
                                space = 1;
                        rcvmem = (tp->advmss + MAX_TCP_HEADER +
                                  16 + sizeof(struct sk_buff));
+                       while (tcp_win_from_space(rcvmem) < tp->advmss)
+                               rcvmem += 128;
                        space *= rcvmem;
                        space = min(space, sysctl_tcp_rmem[2]);
-                       if (space > sk->sk_rcvbuf)
+                       if (space > sk->sk_rcvbuf) {
                                sk->sk_rcvbuf = space;
+
+                               /* Make the window clamp follow along.  */
+                               tp->window_clamp = new_clamp;
+                       }
                }
        }