Bug 2074 - DCE Linux memory defaults too low to allow Linux TCP to ha…

…ve >32767 byte window

The default behavior of TCP in DCE Linux is to allow a maximum window
size of around 32kB.

This is because requests by the Linux sockets/TCP code to allocate
additional buffer memory fail.

In kernel code file ./net/core/sock.c (sk_init), the value of
totalram_pages is zero, so the sysctl wmem and rmem values (default &
max) are set to 32767. totalram_pages is set to zero in kernel code file
./arch/sim/glue.c.

Since one of the main reasons for using DCE Linux is to have realistic
network code behavior, it is disappointing for the default behavior to
be crippled in this way.

I would recommend changing it so that the default behavior is more
realistic. This can be achieved in many ways, but I would request that
it not require extra code on the part of the NS3 user (e.g. running
sysctl commands or calling other functions to set the memory available).
My reason for this request is that this would be an extra step that a
user should not have to take.

Reported-by: Chip Webb
Signed-off-by: Hajime Tazaki <tazaki@sfc.wide.ad.jp>

arch/sim/glue.c

@@ -44,7 +44,7 @@ struct uts_namespace init_uts_ns = {
 
 // XXX: used in network stack !
 unsigned long num_physpages = 0;
-unsigned long totalram_pages = 0;
+unsigned long totalram_pages = 8192;
 
 // XXX figure out initial value
 unsigned int interrupt_pending = 0;