tcp: calculate tcp_mem based on low memory instead of all memory

The tcp_mem array which contains limits on the total amount of memory
used by TCP sockets is calculated based on nr_all_pages.  On a 32 bits
x86 system, we should base this on the number of lowmem pages.
Signed-off-by: NMiquel van Smoorenburg <miquels@cistron.nl>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/tcp.c

@@ -260,6 +260,8 @@
 #include <linux/socket.h>
 #include <linux/random.h>
 #include <linux/bootmem.h>
+#include <linux/highmem.h>
+#include <linux/swap.h>
 #include <linux/cache.h>
 #include <linux/err.h>
 #include <linux/crypto.h>
@@ -2620,7 +2622,7 @@ __setup("thash_entries=", set_thash_entries);
 void __init tcp_init(void)
 {
 	struct sk_buff *skb = NULL;
-	unsigned long limit;
+	unsigned long nr_pages, limit;
 	int order, i, max_share;
 
 	BUILD_BUG_ON(sizeof(struct tcp_skb_cb) > sizeof(skb->cb));
@@ -2689,8 +2691,9 @@ void __init tcp_init(void)
 	 * is up to 1/2 at 256 MB, decreasing toward zero with the amount of
 	 * memory, with a floor of 128 pages.
 	 */
-	limit = min(nr_all_pages, 1UL<<(28-PAGE_SHIFT)) >> (20-PAGE_SHIFT);
-	limit = (limit * (nr_all_pages >> (20-PAGE_SHIFT))) >> (PAGE_SHIFT-11);
+	nr_pages = totalram_pages - totalhigh_pages;
+	limit = min(nr_pages, 1UL<<(28-PAGE_SHIFT)) >> (20-PAGE_SHIFT);
+	limit = (limit * (nr_pages >> (20-PAGE_SHIFT))) >> (PAGE_SHIFT-11);
 	limit = max(limit, 128UL);
 	sysctl_tcp_mem[0] = limit / 4 * 3;
 	sysctl_tcp_mem[1] = limit;