ip_vs_dh.c

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/*
 * IPVS:        Destination Hashing scheduling module
 *
 * Authors:     Wensong Zhang <[email protected]>
 *
 *              Inspired by the consistent hashing scheduler patch from
 *              Thomas Proell <[email protected]>
 *
 *              This program is free software; you can redistribute it and/or
 *              modify it under the terms of the GNU General Public License
 *              as published by the Free Software Foundation; either version
 *              2 of the License, or (at your option) any later version.
 *
 * Changes:
 *
 */

/*
 * The dh algorithm is to select server by the hash key of destination IP
 * address. The pseudo code is as follows:
 *
 *       n <- servernode[dest_ip];
 *       if (n is dead) OR
 *          (n is overloaded) OR (n.weight <= 0) then
 *                 return NULL;
 *
 *       return n;
 *
 * Notes that servernode is a 256-bucket hash table that maps the hash
 * index derived from packet destination IP address to the current server
 * array. If the dh scheduler is used in cache cluster, it is good to
 * combine it with cache_bypass feature. When the statically assigned
 * server is dead or overloaded, the load balancer can bypass the cache
 * server and send requests to the original server directly.
 *
 */

#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>


/*
 *      IPVS DH bucket
 */
struct ip_vs_dh_bucket {
    struct ip_vs_dest       *dest;          /* real server (cache) */
};

/*
 *     for IPVS DH entry hash table
 */
#ifndef CONFIG_IP_VS_DH_TAB_BITS
#define CONFIG_IP_VS_DH_TAB_BITS        8
#endif
#define IP_VS_DH_TAB_BITS               CONFIG_IP_VS_DH_TAB_BITS
#define IP_VS_DH_TAB_SIZE               (1 << IP_VS_DH_TAB_BITS)
#define IP_VS_DH_TAB_MASK               (IP_VS_DH_TAB_SIZE - 1)


/*
 *  Returns hash value for IPVS DH entry
 */
static inline unsigned int ip_vs_dh_hashkey(int af, const union nf_inet_addr *addr)
{
    __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
    return (ntohl(addr_fold)*2654435761UL) & IP_VS_DH_TAB_MASK;
}


/*
 *      Get ip_vs_dest associated with supplied parameters.
 */
static inline struct ip_vs_dest *
ip_vs_dh_get(int af, struct ip_vs_dh_bucket *tbl,
         const union nf_inet_addr *addr)
{
    return (tbl[ip_vs_dh_hashkey(af, addr)]).dest;
}


/*
 *      Assign all the hash buckets of the specified table with the service.
 */
static int
ip_vs_dh_assign(struct ip_vs_dh_bucket *tbl, struct ip_vs_service *svc)
{
    int i;
    struct ip_vs_dh_bucket *b;
    struct list_head *p;
    struct ip_vs_dest *dest;

    b = tbl;
    p = &svc->destinations;
    for (i=0; i<IP_VS_DH_TAB_SIZE; i++) {
        if (list_empty(p)) {
            b->dest = NULL;
        } else {
            if (p == &svc->destinations)
                p = p->next;

            dest = list_entry(p, struct ip_vs_dest, n_list);
            atomic_inc(&dest->refcnt);
            b->dest = dest;

            p = p->next;
        }
        b++;
    }
    return 0;
}


/*
 *      Flush all the hash buckets of the specified table.
 */
static void ip_vs_dh_flush(struct ip_vs_dh_bucket *tbl)
{
    int i;
    struct ip_vs_dh_bucket *b;

    b = tbl;
    for (i=0; i<IP_VS_DH_TAB_SIZE; i++) {
        if (b->dest) {
            atomic_dec(&b->dest->refcnt);
            b->dest = NULL;
        }
        b++;
    }
}


static int ip_vs_dh_init_svc(struct ip_vs_service *svc)
{
    struct ip_vs_dh_bucket *tbl;

    /* allocate the DH table for this service */
    tbl = kmalloc(sizeof(struct ip_vs_dh_bucket)*IP_VS_DH_TAB_SIZE,
              GFP_KERNEL);
    if (tbl == NULL)
        return -ENOMEM;

    svc->sched_data = tbl;
    IP_VS_DBG(6, "DH hash table (memory=%Zdbytes) allocated for "
          "current service\n",
          sizeof(struct ip_vs_dh_bucket)*IP_VS_DH_TAB_SIZE);

    /* assign the hash buckets with the updated service */
    ip_vs_dh_assign(tbl, svc);

    return 0;
}


static int ip_vs_dh_done_svc(struct ip_vs_service *svc)
{
    struct ip_vs_dh_bucket *tbl = svc->sched_data;

    /* got to clean up hash buckets here */
    ip_vs_dh_flush(tbl);

    /* release the table itself */
    kfree(svc->sched_data);
    IP_VS_DBG(6, "DH hash table (memory=%Zdbytes) released\n",
          sizeof(struct ip_vs_dh_bucket)*IP_VS_DH_TAB_SIZE);

    return 0;
}


static int ip_vs_dh_update_svc(struct ip_vs_service *svc)
{
    struct ip_vs_dh_bucket *tbl = svc->sched_data;

    /* got to clean up hash buckets here */
    ip_vs_dh_flush(tbl);

    /* assign the hash buckets with the updated service */
    ip_vs_dh_assign(tbl, svc);

    return 0;
}


/*
 *      If the dest flags is set with IP_VS_DEST_F_OVERLOAD,
 *      consider that the server is overloaded here.
 */
static inline int is_overloaded(struct ip_vs_dest *dest)
{
    return dest->flags & IP_VS_DEST_F_OVERLOAD;
}


/*
 *      Destination hashing scheduling
 */
static struct ip_vs_dest *
ip_vs_dh_schedule(struct ip_vs_service *svc, const struct sk_buff *skb)
{
    struct ip_vs_dest *dest;
    struct ip_vs_dh_bucket *tbl;
    struct ip_vs_iphdr iph;

    ip_vs_fill_iphdr(svc->af, skb_network_header(skb), &iph);

    IP_VS_DBG(6, "%s(): Scheduling...\n", __func__);

    tbl = (struct ip_vs_dh_bucket *)svc->sched_data;
    dest = ip_vs_dh_get(svc->af, tbl, &iph.daddr);
    if (!dest
        || !(dest->flags & IP_VS_DEST_F_AVAILABLE)
        || atomic_read(&dest->weight) <= 0
        || is_overloaded(dest)) {
        return NULL;
    }

    IP_VS_DBG_BUF(6, "DH: destination IP address %s --> server %s:%d\n",
              IP_VS_DBG_ADDR(svc->af, &iph.daddr),
              IP_VS_DBG_ADDR(svc->af, &dest->addr),
              ntohs(dest->port));

    return dest;
}


/*
 *      IPVS DH Scheduler structure
 */
static struct ip_vs_scheduler ip_vs_dh_scheduler =
{
    .name =         "dh",
    .refcnt =       ATOMIC_INIT(0),
    .module =       THIS_MODULE,
    .n_list =       LIST_HEAD_INIT(ip_vs_dh_scheduler.n_list),
    .init_service =     ip_vs_dh_init_svc,
    .done_service =     ip_vs_dh_done_svc,
    .update_service =   ip_vs_dh_update_svc,
    .schedule =     ip_vs_dh_schedule,
};


static int __init ip_vs_dh_init(void)
{
    return register_ip_vs_scheduler(&ip_vs_dh_scheduler);
}


static void __exit ip_vs_dh_cleanup(void)
{
    unregister_ip_vs_scheduler(&ip_vs_dh_scheduler);
}


module_init(ip_vs_dh_init);
module_exit(ip_vs_dh_cleanup);
MODULE_LICENSE("GPL");