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>
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index a34f5cf..37755cc 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3229,7 +3229,6 @@
 
 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 @@
 	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);