tcp: properly initialize tcp memory limits

Commit 4acb4190 tries to fix the using uninitialized value
introduced by commit 3dc43e3,  but it would make the
per-socket memory limits too small.

This patch fixes this and also remove the redundant codes
introduced in 4acb4190.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Acked-by: Glauber Costa <glommer@parallels.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/sysctl_net_ipv4.c

@@ -778,7 +778,6 @@ EXPORT_SYMBOL_GPL(net_ipv4_ctl_path);
 static __net_init int ipv4_sysctl_init_net(struct net *net)
 {
 	struct ctl_table *table;
-	unsigned long limit;
 
 	table = ipv4_net_table;
 	if (!net_eq(net, &init_net)) {
@@ -815,11 +814,6 @@ static __net_init int ipv4_sysctl_init_net(struct net *net)
 	net->ipv4.sysctl_rt_cache_rebuild_count = 4;
 
 	tcp_init_mem(net);
-	limit = nr_free_buffer_pages() / 8;
-	limit = max(limit, 128UL);
-	net->ipv4.sysctl_tcp_mem[0] = limit / 4 * 3;
-	net->ipv4.sysctl_tcp_mem[1] = limit;
-	net->ipv4.sysctl_tcp_mem[2] = net->ipv4.sysctl_tcp_mem[0] * 2;
 
 	net->ipv4.ipv4_hdr = register_net_sysctl_table(net,
 			net_ipv4_ctl_path, table);

net/ipv4/tcp.c

@@ -3229,7 +3229,6 @@ __setup("thash_entries=", set_thash_entries);
 
 void tcp_init_mem(struct net *net)
 {
-	/* Set per-socket limits to no more than 1/128 the pressure threshold */
 	unsigned long limit = nr_free_buffer_pages() / 8;
 	limit = max(limit, 128UL);
 	net->ipv4.sysctl_tcp_mem[0] = limit / 4 * 3;
@@ -3298,7 +3297,8 @@ void __init tcp_init(void)
 	sysctl_max_syn_backlog = max(128, cnt / 256);
 
 	tcp_init_mem(&init_net);
-	limit = nr_free_buffer_pages() / 8;
+	/* Set per-socket limits to no more than 1/128 the pressure threshold */
+	limit = nr_free_buffer_pages() << (PAGE_SHIFT - 10);
 	limit = max(limit, 128UL);
 	max_share = min(4UL*1024*1024, limit);