Implements the Google's Maglev hashing algorithm as a IPVS scheduler.
Basically it provides consistent hashing but offers some special
features about disruption and load balancing.
1) minimal disruption: when the set of destinations changes,
a connection will likely be sent to the same destination
as it was before.
2) load balancing: each destination will receive an almost
equal number of connections.
Seel also for detail: [3.4 Consistent Hasing] in
https://www.usenix.org/system/files/conference/nsdi16/nsdi16-paper-eisenbud.pdf
Signed-off-by: Inju Song <inju.song@xxxxxxxxxxxxx>
---
net/netfilter/ipvs/ip_vs_mh.c | 532 ++++++++++++++++++++++++++++++++++++++++++
1 file changed, 532 insertions(+)
create mode 100644 net/netfilter/ipvs/ip_vs_mh.c
diff --git a/net/netfilter/ipvs/ip_vs_mh.c b/net/netfilter/ipvs/ip_vs_mh.c
new file mode 100644
index 0000000..e531100
--- /dev/null
+++ b/net/netfilter/ipvs/ip_vs_mh.c
@@ -0,0 +1,532 @@
+// SPDX-License-Identifier: GPL-2.0
+/* IPVS: Maglev Hashing scheduling module
+ *
+ * Authors: Inju Song <inju.song@xxxxxxxxxxxxx>
+ *
+ */
+
+/* The mh algorithm is to assign a preference list of all the lookup
+ * table positions to each destination and populate the table with
+ * the most-preferred position of destinations. Then it is to select
+ * destination with the hash key of source IP address through looking
+ * up a the lookup table.
+ *
+ * The algorithm is detailed in:
+ * [3.4 Consistent Hasing]
+https://www.usenix.org/system/files/conference/nsdi16/nsdi16-paper-eisenbud.pdf
+ *
+ */
+
+#define KMSG_COMPONENT "IPVS"
+#define pr_fmt(fmt) KMSG_COMPONENT ": " fmt
+
+#include <linux/ip.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/skbuff.h>
+
+#include <net/ip_vs.h>
+
+#include <linux/siphash.h>
+#include <linux/bitops.h>
+#include <linux/gcd.h>
+
+#define IP_VS_SVC_F_SCHED_MH_FALLBACK IP_VS_SVC_F_SCHED1 /* MH fallback */
+#define IP_VS_SVC_F_SCHED_MH_PORT IP_VS_SVC_F_SCHED2 /* MH use port */
+
+struct ip_vs_mh_lookup {
+ struct ip_vs_dest __rcu *dest; /* real server (cache) */
+};
+
+struct ip_vs_mh_dest_setup {
+ unsigned int offset; /* starting offset */
+ unsigned int skip; /* skip */
+ unsigned int perm; /* next_offset */
+ int turns; /* weight / gcd() and rshift */
+};
+
+/* Available prime numbers for MH table */
+static int primes[] = {251, 509, 1021, 2039, 4093,
+ 8191, 16381, 32749, 65521, 131071};
+
+/* For IPVS MH entry hash table */
+#ifndef CONFIG_IP_VS_MH_TAB_INDEX
+#define CONFIG_IP_VS_MH_TAB_INDEX 12
+#endif
+#define IP_VS_MH_TAB_BITS (CONFIG_IP_VS_MH_TAB_INDEX / 2)
+#define IP_VS_MH_TAB_INDEX (CONFIG_IP_VS_MH_TAB_INDEX - 8)
+#define IP_VS_MH_TAB_SIZE primes[IP_VS_MH_TAB_INDEX]
+
+struct ip_vs_mh_state {
+ struct rcu_head rcu_head;
+ struct ip_vs_mh_lookup *lookup;
+ struct ip_vs_mh_dest_setup *dest_setup;
+ hsiphash_key_t hash1, hash2;
+ int gcd;
+ int rshift;
+};
+
+static inline void generate_hash_secret(hsiphash_key_t *hash1,
+ hsiphash_key_t *hash2)
+{
+ hash1->key[0] = 2654435761UL;
+ hash1->key[1] = 2654435761UL;
+
+ hash2->key[0] = 2654446892UL;
+ hash2->key[1] = 2654446892UL;
+}
+
+/* Helper function to determine if server is unavailable */
+static inline bool is_unavailable(struct ip_vs_dest *dest)
+{
+ return atomic_read(&dest->weight) <= 0 ||
+ dest->flags & IP_VS_DEST_F_OVERLOAD;
+}
+
+/* Returns hash value for IPVS MH entry */
+static inline unsigned int
+ip_vs_mh_hashkey(int af, const union nf_inet_addr *addr,
+ __be16 port, hsiphash_key_t *key, unsigned int offset)
+{
+ unsigned int v;
+ __be32 addr_fold = addr->ip;
+
+#ifdef CONFIG_IP_VS_IPV6
+ if (af == AF_INET6)
+ addr_fold = addr->ip6[0] ^ addr->ip6[1] ^
+ addr->ip6[2] ^ addr->ip6[3];
+#endif
+ v = (offset + ntohs(port) + ntohl(addr_fold));
+ return hsiphash(&v, sizeof(v), key);
+}
+
+/* Reset all the hash buckets of the specified table. */
+static void ip_vs_mh_reset(struct ip_vs_mh_state *s)
+{
+ int i;
+ struct ip_vs_mh_lookup *l;
+ struct ip_vs_dest *dest;
+
+ l = &s->lookup[0];
+ for (i = 0; i < IP_VS_MH_TAB_SIZE; i++) {
+ dest = rcu_dereference_protected(l->dest, 1);
+ if (dest) {
+ ip_vs_dest_put(dest);
+ RCU_INIT_POINTER(l->dest, NULL);
+ }
+ l++;
+ }
+}
+
+static int ip_vs_mh_permutate(struct ip_vs_mh_state *s,
+ struct ip_vs_service *svc)
+{
+ struct list_head *p;
+ struct ip_vs_mh_dest_setup *ds;
+ struct ip_vs_dest *dest;
+ int lw;
+
+ /* If gcd is smaller then 1, number of dests or
+ * all last_weight of dests are zero. So, skip
+ * permutation for the dests.
+ */
+ if (s->gcd < 1)
+ return 0;
+
+ /* Set dest_setup for the dests permutation */
+ p = &svc->destinations;
+ ds = &s->dest_setup[0];
+ while ((p = p->next) != &svc->destinations) {
+ dest = list_entry(p, struct ip_vs_dest, n_list);
+
+ ds->offset = ip_vs_mh_hashkey(svc->af, &dest->addr,
+ dest->port, &s->hash1, 0) %
+ IP_VS_MH_TAB_SIZE;
+ ds->skip = ip_vs_mh_hashkey(svc->af, &dest->addr,
+ dest->port, &s->hash2, 0) %
+ (IP_VS_MH_TAB_SIZE - 1) + 1;
+ ds->perm = ds->offset;
+
+ lw = atomic_read(&dest->last_weight);
+ ds->turns = ((lw / s->gcd) >> s->rshift) ? : (lw != 0);
+ ds++;
+ }
+
+ return 0;
+}
+
+static int ip_vs_mh_populate(struct ip_vs_mh_state *s,
+ struct ip_vs_service *svc)
+{
+ int n, c, dt_count;
+ unsigned long *table;
+ struct list_head *p;
+ struct ip_vs_mh_dest_setup *ds;
+ struct ip_vs_dest *dest, *new_dest;
+
+ /* If gcd is smaller then 1, number of dests or
+ * all last_weight of dests are zero. So, skip
+ * the population for the dests and reset lookup table.
+ */
+ if (s->gcd < 1) {
+ ip_vs_mh_reset(s);
+ return 0;
+ }
+
+ table = kcalloc(BITS_TO_LONGS(IP_VS_MH_TAB_SIZE),
+ sizeof(unsigned long), GFP_KERNEL);
+ if (!table)
+ return -ENOMEM;
+
+ p = &svc->destinations;
+ n = 0;
+ dt_count = 0;
+ while (n < IP_VS_MH_TAB_SIZE) {
+ if (p == &svc->destinations)
+ p = p->next;
+
+ ds = &s->dest_setup[0];
+ while (p != &svc->destinations) {
+ /* ignore added server with zero weight */
+ if (ds->turns < 1) {
+ p = p->next;
+ ds++;
+ continue;
+ }
+
+ c = ds->perm;
+ while (test_bit(c, table)) {
+ /* Add skip, mod IP_VS_MH_TAB_SIZE */
+ ds->perm += ds->skip;
+ if (ds->perm >= IP_VS_MH_TAB_SIZE)
+ ds->perm -= IP_VS_MH_TAB_SIZE;
+ c = ds->perm;
+ }
+
+ __set_bit(c, table);
+
+ dest = rcu_dereference_protected(s->lookup[c].dest, 1);
+ new_dest = list_entry(p, struct ip_vs_dest, n_list);
+ if (dest != new_dest) {
+ if (dest)
+ ip_vs_dest_put(dest);
+ ip_vs_dest_hold(new_dest);
+ RCU_INIT_POINTER(s->lookup[c].dest, new_dest);
+ }
+
+ if (++n == IP_VS_MH_TAB_SIZE)
+ goto out;
+
+ if (++dt_count >= ds->turns) {
+ dt_count = 0;
+ p = p->next;
+ ds++;
+ }
+ }
+ }
+
+out:
+ kfree(table);
+ return 0;
+}
+
+/* Get ip_vs_dest associated with supplied parameters. */
+static inline struct ip_vs_dest *
+ip_vs_mh_get(struct ip_vs_service *svc, struct ip_vs_mh_state *s,
+ const union nf_inet_addr *addr, __be16 port)
+{
+ unsigned int hash = ip_vs_mh_hashkey(svc->af, addr, port, &s->hash1, 0)
+ % IP_VS_MH_TAB_SIZE;
+ struct ip_vs_dest *dest = rcu_dereference(s->lookup[hash].dest);
+
+ return (!dest || is_unavailable(dest)) ? NULL : dest;
+}
+
+/* As ip_vs_mh_get, but with fallback if selected server is unavailable */
+static inline struct ip_vs_dest *
+ip_vs_mh_get_fallback(struct ip_vs_service *svc, struct ip_vs_mh_state *s,
+ const union nf_inet_addr *addr, __be16 port)
+{
+ unsigned int offset, roffset;
+ unsigned int hash, ihash;
+ struct ip_vs_dest *dest;
+
+ /* first try the dest it's supposed to go to */
+ ihash = ip_vs_mh_hashkey(svc->af, addr, port,
+ &s->hash1, 0) % IP_VS_MH_TAB_SIZE;
+ dest = rcu_dereference(s->lookup[ihash].dest);
+ if (!dest)
+ return NULL;
+ if (!is_unavailable(dest))
+ return dest;
+
+ IP_VS_DBG_BUF(6, "MH: selected unavailable server %s:%d, reselecting",
+ IP_VS_DBG_ADDR(dest->af, &dest->addr), ntohs(dest->port));
+
+ /* if the original dest is unavailable, loop around the table
+ * starting from ihash to find a new dest
+ */
+ for (offset = 0; offset < IP_VS_MH_TAB_SIZE; offset++) {
+ roffset = (offset + ihash) % IP_VS_MH_TAB_SIZE;
+ hash = ip_vs_mh_hashkey(svc->af, addr, port, &s->hash1,
+ roffset) % IP_VS_MH_TAB_SIZE;
+ dest = rcu_dereference(s->lookup[hash].dest);
+ if (!dest)
+ break;
+ if (!is_unavailable(dest))
+ return dest;
+ IP_VS_DBG_BUF(6,
+ "MH: selected unavailable server %s:%d (offset %d), reselecting",
+ IP_VS_DBG_ADDR(dest->af, &dest->addr),
+ ntohs(dest->port), roffset);
+ }
+
+ return NULL;
+}
+
+/* Assign all the hash buckets of the specified table with the service. */
+static int ip_vs_mh_reassign(struct ip_vs_mh_state *s,
+ struct ip_vs_service *svc)
+{
+ int ret;
+
+ if (svc->num_dests > IP_VS_MH_TAB_SIZE)
+ return -EINVAL;
+
+ if (svc->num_dests >= 1) {
+ s->dest_setup = kcalloc(svc->num_dests,
+ sizeof(struct ip_vs_mh_dest_setup),
+ GFP_KERNEL);
+ if (!s->dest_setup)
+ return -ENOMEM;
+ }
+
+ ip_vs_mh_permutate(s, svc);
+
+ ret = ip_vs_mh_populate(s, svc);
+ if (ret < 0)
+ goto out;
+
+ IP_VS_DBG_BUF(6, "MH: reassign lookup table of %s:%d\n",
+ IP_VS_DBG_ADDR(svc->af, &svc->addr),
+ ntohs(svc->port));
+
+out:
+ if (svc->num_dests >= 1) {
+ kfree(s->dest_setup);
+ s->dest_setup = NULL;
+ }
+ return ret;
+}
+
+static int ip_vs_mh_gcd_weight(struct ip_vs_service *svc)
+{
+ struct ip_vs_dest *dest;
+ int weight;
+ int g = 0;
+
+ list_for_each_entry(dest, &svc->destinations, n_list) {
+ weight = atomic_read(&dest->last_weight);
+ if (weight > 0) {
+ if (g > 0)
+ g = gcd(weight, g);
+ else
+ g = weight;
+ }
+ }
+ return g;
+}
+
+/* To avoid assigning huge weight for the MH table,
+ * calculate shift value with gcd.
+ */
+static int ip_vs_mh_shift_weight(struct ip_vs_service *svc, int gcd)
+{
+ struct ip_vs_dest *dest;
+ int new_weight, weight = 0;
+ int mw, shift;
+
+ /* If gcd is smaller then 1, number of dests or
+ * all last_weight of dests are zero. So, return
+ * shift value as zero.
+ */
+ if (gcd < 1)
+ return 0;
+
+ list_for_each_entry(dest, &svc->destinations, n_list) {
+ new_weight = atomic_read(&dest->last_weight);
+ if (new_weight > weight)
+ weight = new_weight;
+ }
+
+ /* Because gcd is greater than zero,
+ * the maximum weight and gcd are always greater than zero
+ */
+ mw = weight / gcd;
+
+ /* shift = occupied bits of weight/gcd - MH highest bits */
+ shift = fls(mw) - IP_VS_MH_TAB_BITS;
+ return (shift >= 0) ? shift : 0;
+}
+
+static void ip_vs_mh_state_free(struct rcu_head *head)
+{
+ struct ip_vs_mh_state *s;
+
+ s = container_of(head, struct ip_vs_mh_state, rcu_head);
+ kfree(s->lookup);
+ kfree(s);
+}
+
+static int ip_vs_mh_init_svc(struct ip_vs_service *svc)
+{
+ struct ip_vs_mh_state *s;
+
+ /* allocate the MH table for this service */
+ s = kzalloc(sizeof(*s), GFP_KERNEL);
+ if (!s)
+ return -ENOMEM;
+
+ s->lookup = kcalloc(IP_VS_MH_TAB_SIZE, sizeof(struct ip_vs_mh_lookup),
+ GFP_KERNEL);
+ if (!s->lookup) {
+ kfree(s);
+ return -ENOMEM;
+ }
+
+ generate_hash_secret(&s->hash1, &s->hash2);
+ s->gcd = ip_vs_mh_gcd_weight(svc);
+ s->rshift = ip_vs_mh_shift_weight(svc, s->gcd);
+
+ svc->sched_data = s;
+ IP_VS_DBG(6,
+ "MH lookup table (memory=%zdbytes) allocated for current service\n",
+ sizeof(struct ip_vs_mh_lookup) * IP_VS_MH_TAB_SIZE);
+
+ /* permutate & populate with current dests */
+ return ip_vs_mh_reassign(s, svc);
+}
+
+static void ip_vs_mh_done_svc(struct ip_vs_service *svc)
+{
+ struct ip_vs_mh_state *s = svc->sched_data;
+
+ /* got to clean up hash buckets here */
+ ip_vs_mh_reset(s);
+
+ /* release the table itself */
+ ip_vs_mh_state_free(&s->rcu_head);
+ IP_VS_DBG(6, "MH lookup table (memory=%zdbytes) released\n",
+ sizeof(struct ip_vs_mh_lookup) * IP_VS_MH_TAB_SIZE);
+}
+
+static int ip_vs_mh_dest_changed(struct ip_vs_service *svc,
+ struct ip_vs_dest *dest)
+{
+ struct ip_vs_mh_state *s = svc->sched_data;
+
+ s->gcd = ip_vs_mh_gcd_weight(svc);
+ s->rshift = ip_vs_mh_shift_weight(svc, s->gcd);
+
+ /* assign the hash buckets with the updated service */
+ return ip_vs_mh_reassign(s, svc);
+}
+
+/* Helper function to get port number */
+static inline __be16
+ip_vs_mh_get_port(const struct sk_buff *skb, struct ip_vs_iphdr *iph)
+{
+ __be16 _ports[2], *ports;
+
+ /* At this point we know that we have a valid packet of some kind.
+ * Because ICMP packets are only guaranteed to have the first 8
+ * bytes, let's just grab the ports. Fortunately they're in the
+ * same position for all three of the protocols we care about.
+ */
+ switch (iph->protocol) {
+ case IPPROTO_TCP:
+ case IPPROTO_UDP:
+ case IPPROTO_SCTP:
+ ports = skb_header_pointer(skb, iph->len, sizeof(_ports),
+ &_ports);
+ if (unlikely(!ports))
+ return 0;
+
+ if (likely(!ip_vs_iph_inverse(iph)))
+ return ports[0];
+ else
+ return ports[1];
+ default:
+ return 0;
+ }
+}
+
+/* Maglev Hashing scheduling */
+static struct ip_vs_dest *
+ip_vs_mh_schedule(struct ip_vs_service *svc, const struct sk_buff *skb,
+ struct ip_vs_iphdr *iph)
+{
+ struct ip_vs_dest *dest;
+ struct ip_vs_mh_state *s;
+ __be16 port = 0;
+ const union nf_inet_addr *hash_addr;
+
+ hash_addr = ip_vs_iph_inverse(iph) ? &iph->daddr : &iph->saddr;
+
+ IP_VS_DBG(6, "%s : Scheduling...\n", __func__);
+
+ if (svc->flags & IP_VS_SVC_F_SCHED_MH_PORT)
+ port = ip_vs_mh_get_port(skb, iph);
+
+ s = (struct ip_vs_mh_state *)svc->sched_data;
+
+ if (svc->flags & IP_VS_SVC_F_SCHED_MH_FALLBACK)
+ dest = ip_vs_mh_get_fallback(svc, s, hash_addr, port);
+ else
+ dest = ip_vs_mh_get(svc, s, hash_addr, port);
+
+ if (!dest) {
+ ip_vs_scheduler_err(svc, "no destination available");
+ return NULL;
+ }
+
+ IP_VS_DBG_BUF(6, "MH: source IP address %s:%d --> server %s:%d\n",
+ IP_VS_DBG_ADDR(svc->af, hash_addr),
+ ntohs(port),
+ IP_VS_DBG_ADDR(dest->af, &dest->addr),
+ ntohs(dest->port));
+
+ return dest;
+}
+
+/* IPVS MH Scheduler structure */
+static struct ip_vs_scheduler ip_vs_mh_scheduler = {
+ .name = "mh",
+ .refcnt = ATOMIC_INIT(0),
+ .module = THIS_MODULE,
+ .n_list = LIST_HEAD_INIT(ip_vs_mh_scheduler.n_list),
+ .init_service = ip_vs_mh_init_svc,
+ .done_service = ip_vs_mh_done_svc,
+ .add_dest = ip_vs_mh_dest_changed,
+ .del_dest = ip_vs_mh_dest_changed,
+ .upd_dest = ip_vs_mh_dest_changed,
+ .schedule = ip_vs_mh_schedule,
+};
+
+static int __init ip_vs_mh_init(void)
+{
+ return register_ip_vs_scheduler(&ip_vs_mh_scheduler);
+}
+
+static void __exit ip_vs_mh_cleanup(void)
+{
+ unregister_ip_vs_scheduler(&ip_vs_mh_scheduler);
+ rcu_barrier();
+}
+
+module_init(ip_vs_mh_init);
+module_exit(ip_vs_mh_cleanup);
+MODULE_DESCRIPTION("Maglev hashing ipvs scheduler");
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Inju Song <inju.song@xxxxxxxxxxxxx>");
--
1.8.3.1
--
Inju Song
NAVER Corporation
--
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