net: refine {udp|tcp|sctp}_mem limits

Current tcp/udp/sctp global memory limits are not taking into account
hugepages allocations, and allow 50% of ram to be used by buffers of a
single protocol [ not counting space used by sockets / inodes ...]

Lets use nr_free_buffer_pages() and allow a default of 1/8 of kernel ram
per protocol, and a minimum of 128 pages.
Heavy duty machines sysadmins probably need to tweak limits anyway.


References: https://bugzilla.stlinux.com/show_bug.cgi?id=38032
Reported-by: starlight <starlight@binnacle.cx>
Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/tcp.c

@@ -3220,7 +3220,7 @@ __setup("thash_entries=", set_thash_entries);
 void __init tcp_init(void)
 {
 	struct sk_buff *skb = NULL;
-	unsigned long nr_pages, limit;
+	unsigned long limit;
 	int i, max_share, cnt;
 	unsigned long jiffy = jiffies;
 
@@ -3277,13 +3277,7 @@ void __init tcp_init(void)
 	sysctl_tcp_max_orphans = cnt / 2;
 	sysctl_max_syn_backlog = max(128, cnt / 256);
 
-	/* Set the pressure threshold to be a fraction of global memory that
-	 * is up to 1/2 at 256 MB, decreasing toward zero with the amount of
-	 * memory, with a floor of 128 pages.
-	 */
-	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 = nr_free_buffer_pages() / 8;
 	limit = max(limit, 128UL);
 	sysctl_tcp_mem[0] = limit / 4 * 3;
 	sysctl_tcp_mem[1] = limit;

net/ipv4/udp.c

@@ -2209,16 +2209,10 @@ void __init udp_table_init(struct udp_table *table, const char *name)
 
 void __init udp_init(void)
 {
-	unsigned long nr_pages, limit;
+	unsigned long limit;
 
 	udp_table_init(&udp_table, "UDP");
-	/* Set the pressure threshold up by the same strategy of TCP. It is a
-	 * fraction of global memory that is up to 1/2 at 256 MB, decreasing
-	 * toward zero with the amount of memory, with a floor of 128 pages.
-	 */
-	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 = nr_free_buffer_pages() / 8;
 	limit = max(limit, 128UL);
 	sysctl_udp_mem[0] = limit / 4 * 3;
 	sysctl_udp_mem[1] = limit;

net/sctp/protocol.c

@@ -1058,7 +1058,6 @@ SCTP_STATIC __init int sctp_init(void)
 	int status = -EINVAL;
 	unsigned long goal;
 	unsigned long limit;
-	unsigned long nr_pages;
 	int max_share;
 	int order;
 
@@ -1148,15 +1147,7 @@ SCTP_STATIC __init int sctp_init(void)
 	/* Initialize handle used for association ids. */
 	idr_init(&sctp_assocs_id);
 
-	/* Set the pressure threshold to be a fraction of global memory that
-	 * is up to 1/2 at 256 MB, decreasing toward zero with the amount of
-	 * memory, with a floor of 128 pages.
-	 * Note this initializes the data in sctpv6_prot too
-	 * Unabashedly stolen from tcp_init
-	 */
-	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 = nr_free_buffer_pages() / 8;
 	limit = max(limit, 128UL);
 	sysctl_sctp_mem[0] = limit / 4 * 3;
 	sysctl_sctp_mem[1] = limit;