[TCP]: Set default max buffers from memory pool size

This patch sets the maximum TCP buffer sizes (available to automatic
buffer tuning, not to setsockopt) based on the TCP memory pool size.
The maximum sndbuf and rcvbuf each will be up to 4 MB, but no more
than 1/128 of the memory pressure threshold.
Signed-off-by: John Heffner <jheffner@psc.edu>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/tcp.c

@@ -276,8 +276,8 @@ atomic_t tcp_orphan_count = ATOMIC_INIT(0);
 EXPORT_SYMBOL_GPL(tcp_orphan_count);
 
 int sysctl_tcp_mem[3];
-int sysctl_tcp_wmem[3] = { 4 * 1024, 16 * 1024, 128 * 1024 };
-int sysctl_tcp_rmem[3] = { 4 * 1024, 87380, 87380 * 2 };
+int sysctl_tcp_wmem[3];
+int sysctl_tcp_rmem[3];
 
 EXPORT_SYMBOL(sysctl_tcp_mem);
 EXPORT_SYMBOL(sysctl_tcp_rmem);
@@ -2081,7 +2081,8 @@ __setup("thash_entries=", set_thash_entries);
 void __init tcp_init(void)
 {
 	struct sk_buff *skb = NULL;
-	int order, i;
+	unsigned long limit;
+	int order, i, max_share;
 
 	if (sizeof(struct tcp_skb_cb) > sizeof(skb->cb))
 		__skb_cb_too_small_for_tcp(sizeof(struct tcp_skb_cb),
@@ -2155,12 +2156,16 @@ void __init tcp_init(void)
 	sysctl_tcp_mem[1] = 1024 << order;
 	sysctl_tcp_mem[2] = 1536 << order;
 
-	if (order < 3) {
-		sysctl_tcp_wmem[2] = 64 * 1024;
-		sysctl_tcp_rmem[0] = PAGE_SIZE;
-		sysctl_tcp_rmem[1] = 43689;
-		sysctl_tcp_rmem[2] = 2 * 43689;
-	}
+	limit = ((unsigned long)sysctl_tcp_mem[1]) << (PAGE_SHIFT - 7);
+	max_share = min(4UL*1024*1024, limit);
+
+	sysctl_tcp_wmem[0] = SK_STREAM_MEM_QUANTUM;
+	sysctl_tcp_wmem[1] = 16*1024;
+	sysctl_tcp_wmem[2] = max(64*1024, max_share);
+
+	sysctl_tcp_rmem[0] = SK_STREAM_MEM_QUANTUM;
+	sysctl_tcp_rmem[1] = 87380;
+	sysctl_tcp_rmem[2] = max(87380, max_share);
 
 	printk(KERN_INFO "TCP: Hash tables configured "
 	       "(established %d bind %d)\n",