Merge git://git.kernel.org/pub/scm/linux/kernel/git/pablo/nf-next

Pablo Neira Ayuso says:

====================
Netfilter/IPVS updates for net-next

1) Remove indirection and use nf_ct_get() instead from nfnetlink_log
   and nfnetlink_queue, from Florian Westphal.

2) Add weighted random twos choice least-connection scheduling for IPVS,
   from Darby Payne.

3) Add a __hash placeholder in the flow tuple structure to identify
   the field to be included in the rhashtable key hash calculation.

4) Add a new nft_parse_register_load() and nft_parse_register_store()
   to consolidate register load and store in the core.

5) Statify nft_parse_register() since it has no more module clients.

6) Remove redundant assignment in nft_cmp, from Colin Ian King.

* git://git.kernel.org/pub/scm/linux/kernel/git/pablo/nf-next:
  netfilter: nftables: remove redundant assignment of variable err
  netfilter: nftables: statify nft_parse_register()
  netfilter: nftables: add nft_parse_register_store() and use it
  netfilter: nftables: add nft_parse_register_load() and use it
  netfilter: flowtable: add hash offset field to tuple
  ipvs: add weighted random twos choice algorithm
  netfilter: ctnetlink: remove get_ct indirection
====================

Link: https://lore.kernel.org/r/20210206015005.23037-1-pablo@netfilter.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/netfilter/ipvs/Kconfig

@@ -271,6 +271,17 @@ config	IP_VS_NQ
 	  If you want to compile it in kernel, say Y. To compile it as a
 	  module, choose M here. If unsure, say N.
 
+config	IP_VS_TWOS
+	tristate "weighted random twos choice least-connection scheduling"
+	help
+	  The weighted random twos choice least-connection scheduling
+	  algorithm picks two random real servers and directs network
+	  connections to the server with the least active connections
+	  normalized by the server weight.
+
+	  If you want to compile it in kernel, say Y. To compile it as a
+	  module, choose M here. If unsure, say N.
+
 comment 'IPVS SH scheduler'
 
 config IP_VS_SH_TAB_BITS

net/netfilter/ipvs/Makefile

@@ -36,6 +36,7 @@ obj-$(CONFIG_IP_VS_SH) += ip_vs_sh.o
 obj-$(CONFIG_IP_VS_MH) += ip_vs_mh.o
 obj-$(CONFIG_IP_VS_SED) += ip_vs_sed.o
 obj-$(CONFIG_IP_VS_NQ) += ip_vs_nq.o
+obj-$(CONFIG_IP_VS_TWOS) += ip_vs_twos.o
 
 # IPVS application helpers
 obj-$(CONFIG_IP_VS_FTP) += ip_vs_ftp.o

net/netfilter/ipvs/ip_vs_twos.c

@@ -0,0 +1,139 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* IPVS:        Power of Twos Choice Scheduling module
+ *
+ * Authors:     Darby Payne <darby.payne@applovin.com>
+ */
+
+#define KMSG_COMPONENT "IPVS"
+#define pr_fmt(fmt) KMSG_COMPONENT ": " fmt
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/random.h>
+
+#include <net/ip_vs.h>
+
+/*    Power of Twos Choice scheduling, algorithm originally described by
+ *    Michael Mitzenmacher.
+ *
+ *    Randomly picks two destinations and picks the one with the least
+ *    amount of connections
+ *
+ *    The algorithm calculates a few variables
+ *    - total_weight = sum of all weights
+ *    - rweight1 = random number between [0,total_weight]
+ *    - rweight2 = random number between [0,total_weight]
+ *
+ *    For each destination
+ *      decrement rweight1 and rweight2 by the destination weight
+ *      pick choice1 when rweight1 is <= 0
+ *      pick choice2 when rweight2 is <= 0
+ *
+ *    Return choice2 if choice2 has less connections than choice 1 normalized
+ *    by weight
+ *
+ * References
+ * ----------
+ *
+ * [Mitzenmacher 2016]
+ *    The Power of Two Random Choices: A Survey of Techniques and Results
+ *    Michael Mitzenmacher, Andrea W. Richa y, Ramesh Sitaraman
+ *    http://www.eecs.harvard.edu/~michaelm/NEWWORK/postscripts/twosurvey.pdf
+ *
+ */
+static struct ip_vs_dest *ip_vs_twos_schedule(struct ip_vs_service *svc,
+					      const struct sk_buff *skb,
+					      struct ip_vs_iphdr *iph)
+{
+	struct ip_vs_dest *dest, *choice1 = NULL, *choice2 = NULL;
+	int rweight1, rweight2, weight1 = -1, weight2 = -1, overhead1 = 0;
+	int overhead2, total_weight = 0, weight;
+
+	IP_VS_DBG(6, "%s(): Scheduling...\n", __func__);
+
+	/* Generate a random weight between [0,sum of all weights) */
+	list_for_each_entry_rcu(dest, &svc->destinations, n_list) {
+		if (!(dest->flags & IP_VS_DEST_F_OVERLOAD)) {
+			weight = atomic_read(&dest->weight);
+			if (weight > 0) {
+				total_weight += weight;
+				choice1 = dest;
+			}
+		}
+	}
+
+	if (!choice1) {
+		ip_vs_scheduler_err(svc, "no destination available");
+		return NULL;
+	}
+
+	/* Add 1 to total_weight so that the random weights are inclusive
+	 * from 0 to total_weight
+	 */
+	total_weight += 1;
+	rweight1 = prandom_u32() % total_weight;
+	rweight2 = prandom_u32() % total_weight;
+
+	/* Pick two weighted servers */
+	list_for_each_entry_rcu(dest, &svc->destinations, n_list) {
+		if (dest->flags & IP_VS_DEST_F_OVERLOAD)
+			continue;
+
+		weight = atomic_read(&dest->weight);
+		if (weight <= 0)
+			continue;
+
+		rweight1 -= weight;
+		rweight2 -= weight;
+
+		if (rweight1 <= 0 && weight1 == -1) {
+			choice1 = dest;
+			weight1 = weight;
+			overhead1 = ip_vs_dest_conn_overhead(dest);
+		}
+
+		if (rweight2 <= 0 && weight2 == -1) {
+			choice2 = dest;
+			weight2 = weight;
+			overhead2 = ip_vs_dest_conn_overhead(dest);
+		}
+
+		if (weight1 != -1 && weight2 != -1)
+			goto nextstage;
+	}
+
+nextstage:
+	if (choice2 && (weight2 * overhead1) > (weight1 * overhead2))
+		choice1 = choice2;
+
+	IP_VS_DBG_BUF(6, "twos: server %s:%u conns %d refcnt %d weight %d\n",
+		      IP_VS_DBG_ADDR(choice1->af, &choice1->addr),
+		      ntohs(choice1->port), atomic_read(&choice1->activeconns),
+		      refcount_read(&choice1->refcnt),
+		      atomic_read(&choice1->weight));
+
+	return choice1;
+}
+
+static struct ip_vs_scheduler ip_vs_twos_scheduler = {
+	.name = "twos",
+	.refcnt = ATOMIC_INIT(0),
+	.module = THIS_MODULE,
+	.n_list = LIST_HEAD_INIT(ip_vs_twos_scheduler.n_list),
+	.schedule = ip_vs_twos_schedule,
+};
+
+static int __init ip_vs_twos_init(void)
+{
+	return register_ip_vs_scheduler(&ip_vs_twos_scheduler);
+}
+
+static void __exit ip_vs_twos_cleanup(void)
+{
+	unregister_ip_vs_scheduler(&ip_vs_twos_scheduler);
+	synchronize_rcu();
+}
+
+module_init(ip_vs_twos_init);
+module_exit(ip_vs_twos_cleanup);
+MODULE_LICENSE("GPL");