[NETFILTER]: ULOG/nfnetlink_log: Use better default value for 'nlbufsiz'

Performance tests showed that ULOG may fail on heavy loaded systems
because of failed order-N allocations (N >= 1).

The default value of 4096 is not optimal in the sense that it actually
allocates _two_ contigous physical pages.  Reasoning: ULOG uses
alloc_skb(), which adds another ~300 bytes for skb_shared_info.

This patch sets the default value to NLMSG_GOODSIZE and adds some
documentation at the top.
Signed-off-by: Holger Eitzenberger <heitzenberger@astaro.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/bridge/netfilter/ebt_ulog.c

@@ -46,7 +46,7 @@
 #define PRINTR(format, args...) do { if (net_ratelimit()) \
                                 printk(format , ## args); } while (0)
 
-static unsigned int nlbufsiz = 4096;
+static unsigned int nlbufsiz = NLMSG_GOODSIZE;
 module_param(nlbufsiz, uint, 0600);
 MODULE_PARM_DESC(nlbufsiz, "netlink buffer size (number of bytes) "
                            "(defaults to 4096)");

net/ipv4/netfilter/ipt_ULOG.c

@@ -35,6 +35,10 @@
  * each nlgroup you are using, so the total kernel memory usage increases
  * by that factor.
  *
+ * Actually you should use nlbufsiz a bit smaller than PAGE_SIZE, since
+ * nlbufsiz is used with alloc_skb, which adds another
+ * sizeof(struct skb_shared_info).  Use NLMSG_GOODSIZE instead.
+ *
  * flushtimeout:
  *   Specify, after how many hundredths of a second the queue should be
  *   flushed even if it is not full yet.
@@ -76,7 +80,7 @@ MODULE_ALIAS_NET_PF_PROTO(PF_NETLINK, NETLINK_NFLOG);
 
 #define PRINTR(format, args...) do { if (net_ratelimit()) printk(format , ## args); } while (0)
 
-static unsigned int nlbufsiz = 4096;
+static unsigned int nlbufsiz = NLMSG_GOODSIZE;
 module_param(nlbufsiz, uint, 0400);
 MODULE_PARM_DESC(nlbufsiz, "netlink buffer size");
 

net/netfilter/nfnetlink_log.c

@@ -37,7 +37,7 @@
 #include "../bridge/br_private.h"
 #endif
 
-#define NFULNL_NLBUFSIZ_DEFAULT	4096
+#define NFULNL_NLBUFSIZ_DEFAULT	NLMSG_GOODSIZE
 #define NFULNL_TIMEOUT_DEFAULT 	100	/* every second */
 #define NFULNL_QTHRESH_DEFAULT 	100	/* 100 packets */