tcp: halves tcp_mem[] limits

Allowing tcp to use ~19% of physical memory is way too much,
and allowed bugs to be hidden. Add to this that some drivers use a full
page per incoming frame, so real cost can be twice the advertized one.

Reduce tcp_mem by 50 % as a first step to sanity.

tcp_mem[0,1,2] defaults are now 4.68%, 6.25%, 9.37% of physical memory.
Signed-off-by: NEric Dumazet <edumazet@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/tcp.c

@@ -3068,11 +3068,12 @@ __setup("thash_entries=", set_thash_entries);
 
 static void __init tcp_init_mem(void)
 {
-	unsigned long limit = nr_free_buffer_pages() / 8;
+	unsigned long limit = nr_free_buffer_pages() / 16;
+
 	limit = max(limit, 128UL);
-	sysctl_tcp_mem[0] = limit / 4 * 3;
-	sysctl_tcp_mem[1] = limit;
-	sysctl_tcp_mem[2] = sysctl_tcp_mem[0] * 2;
+	sysctl_tcp_mem[0] = limit / 4 * 3;		/* 4.68 % */
+	sysctl_tcp_mem[1] = limit;			/* 6.25 % */
+	sysctl_tcp_mem[2] = sysctl_tcp_mem[0] * 2;	/* 9.37 % */
 }
 
 void __init tcp_init(void)