ip_vs_lblc.c

Go to the documentation of this file.

/*
 * IPVS:        Locality-Based Least-Connection scheduling module
 *
 * Authors:     Wensong Zhang <[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:
 *     Martin Hamilton         :    fixed the terrible locking bugs
 *                                   *lock(tbl->lock) ==> *lock(&tbl->lock)
 *     Wensong Zhang           :    fixed the uninitialized tbl->lock bug
 *     Wensong Zhang           :    added doing full expiration check to
 *                                   collect stale entries of 24+ hours when
 *                                   no partial expire check in a half hour
 *     Julian Anastasov        :    replaced del_timer call with del_timer_sync
 *                                   to avoid the possible race between timer
 *                                   handler and del_timer thread in SMP
 *
 */

/*
 * The lblc algorithm is as follows (pseudo code):
 *
 *       if cachenode[dest_ip] is null then
 *               n, cachenode[dest_ip] <- {weighted least-conn node};
 *       else
 *               n <- cachenode[dest_ip];
 *               if (n is dead) OR
 *                  (n.conns>n.weight AND
 *                   there is a node m with m.conns<m.weight/2) then
 *                 n, cachenode[dest_ip] <- {weighted least-conn node};
 *
 *       return n;
 *
 * Thanks must go to Wenzhuo Zhang for talking WCCP to me and pushing
 * me to write this module.
 */

#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 <linux/jiffies.h>

/* for sysctl */
#include <linux/fs.h>
#include <linux/sysctl.h>

#include <net/ip_vs.h>


/*
 *    It is for garbage collection of stale IPVS lblc entries,
 *    when the table is full.
 */
#define CHECK_EXPIRE_INTERVAL   (60*HZ)
#define ENTRY_TIMEOUT           (6*60*HZ)

#define DEFAULT_EXPIRATION  (24*60*60*HZ)

/*
 *    It is for full expiration check.
 *    When there is no partial expiration check (garbage collection)
 *    in a half hour, do a full expiration check to collect stale
 *    entries that haven't been touched for a day.
 */
#define COUNT_FOR_FULL_EXPIRATION   30


/*
 *     for IPVS lblc entry hash table
 */
#ifndef CONFIG_IP_VS_LBLC_TAB_BITS
#define CONFIG_IP_VS_LBLC_TAB_BITS      10
#endif
#define IP_VS_LBLC_TAB_BITS     CONFIG_IP_VS_LBLC_TAB_BITS
#define IP_VS_LBLC_TAB_SIZE     (1 << IP_VS_LBLC_TAB_BITS)
#define IP_VS_LBLC_TAB_MASK     (IP_VS_LBLC_TAB_SIZE - 1)


/*
 *      IPVS lblc entry represents an association between destination
 *      IP address and its destination server
 */
struct ip_vs_lblc_entry {
    struct list_head        list;
    int         af;     /* address family */
    union nf_inet_addr      addr;           /* destination IP address */
    struct ip_vs_dest       *dest;          /* real server (cache) */
    unsigned long           lastuse;        /* last used time */
};


/*
 *      IPVS lblc hash table
 */
struct ip_vs_lblc_table {
    struct list_head        bucket[IP_VS_LBLC_TAB_SIZE];  /* hash bucket */
    atomic_t                entries;        /* number of entries */
    int                     max_size;       /* maximum size of entries */
    struct timer_list       periodic_timer; /* collect stale entries */
    int                     rover;          /* rover for expire check */
    int                     counter;        /* counter for no expire */
};


/*
 *      IPVS LBLC sysctl table
 */
#ifdef CONFIG_SYSCTL
static ctl_table vs_vars_table[] = {
    {
        .procname   = "lblc_expiration",
        .data       = NULL,
        .maxlen     = sizeof(int),
        .mode       = 0644,
        .proc_handler   = proc_dointvec_jiffies,
    },
    { }
};
#endif

static inline void ip_vs_lblc_free(struct ip_vs_lblc_entry *en)
{
    list_del(&en->list);
    /*
     * We don't kfree dest because it is referred either by its service
     * or the trash dest list.
     */
    atomic_dec(&en->dest->refcnt);
    kfree(en);
}


/*
 *  Returns hash value for IPVS LBLC entry
 */
static inline unsigned int
ip_vs_lblc_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_LBLC_TAB_MASK;
}


/*
 *  Hash an entry in the ip_vs_lblc_table.
 *  returns bool success.
 */
static void
ip_vs_lblc_hash(struct ip_vs_lblc_table *tbl, struct ip_vs_lblc_entry *en)
{
    unsigned int hash = ip_vs_lblc_hashkey(en->af, &en->addr);

    list_add(&en->list, &tbl->bucket[hash]);
    atomic_inc(&tbl->entries);
}


/*
 *  Get ip_vs_lblc_entry associated with supplied parameters. Called under read
 *  lock
 */
static inline struct ip_vs_lblc_entry *
ip_vs_lblc_get(int af, struct ip_vs_lblc_table *tbl,
           const union nf_inet_addr *addr)
{
    unsigned int hash = ip_vs_lblc_hashkey(af, addr);
    struct ip_vs_lblc_entry *en;

    list_for_each_entry(en, &tbl->bucket[hash], list)
        if (ip_vs_addr_equal(af, &en->addr, addr))
            return en;

    return NULL;
}


/*
 * Create or update an ip_vs_lblc_entry, which is a mapping of a destination IP
 * address to a server. Called under write lock.
 */
static inline struct ip_vs_lblc_entry *
ip_vs_lblc_new(struct ip_vs_lblc_table *tbl, const union nf_inet_addr *daddr,
           struct ip_vs_dest *dest)
{
    struct ip_vs_lblc_entry *en;

    en = ip_vs_lblc_get(dest->af, tbl, daddr);
    if (!en) {
        en = kmalloc(sizeof(*en), GFP_ATOMIC);
        if (!en)
            return NULL;

        en->af = dest->af;
        ip_vs_addr_copy(dest->af, &en->addr, daddr);
        en->lastuse = jiffies;

        atomic_inc(&dest->refcnt);
        en->dest = dest;

        ip_vs_lblc_hash(tbl, en);
    } else if (en->dest != dest) {
        atomic_dec(&en->dest->refcnt);
        atomic_inc(&dest->refcnt);
        en->dest = dest;
    }

    return en;
}


/*
 *      Flush all the entries of the specified table.
 */
static void ip_vs_lblc_flush(struct ip_vs_lblc_table *tbl)
{
    struct ip_vs_lblc_entry *en, *nxt;
    int i;

    for (i=0; i<IP_VS_LBLC_TAB_SIZE; i++) {
        list_for_each_entry_safe(en, nxt, &tbl->bucket[i], list) {
            ip_vs_lblc_free(en);
            atomic_dec(&tbl->entries);
        }
    }
}

static int sysctl_lblc_expiration(struct ip_vs_service *svc)
{
#ifdef CONFIG_SYSCTL
    struct netns_ipvs *ipvs = net_ipvs(svc->net);
    return ipvs->sysctl_lblc_expiration;
#else
    return DEFAULT_EXPIRATION;
#endif
}

static inline void ip_vs_lblc_full_check(struct ip_vs_service *svc)
{
    struct ip_vs_lblc_table *tbl = svc->sched_data;
    struct ip_vs_lblc_entry *en, *nxt;
    unsigned long now = jiffies;
    int i, j;

    for (i=0, j=tbl->rover; i<IP_VS_LBLC_TAB_SIZE; i++) {
        j = (j + 1) & IP_VS_LBLC_TAB_MASK;

        write_lock(&svc->sched_lock);
        list_for_each_entry_safe(en, nxt, &tbl->bucket[j], list) {
            if (time_before(now,
                    en->lastuse +
                    sysctl_lblc_expiration(svc)))
                continue;

            ip_vs_lblc_free(en);
            atomic_dec(&tbl->entries);
        }
        write_unlock(&svc->sched_lock);
    }
    tbl->rover = j;
}


/*
 *      Periodical timer handler for IPVS lblc table
 *      It is used to collect stale entries when the number of entries
 *      exceeds the maximum size of the table.
 *
 *      Fixme: we probably need more complicated algorithm to collect
 *             entries that have not been used for a long time even
 *             if the number of entries doesn't exceed the maximum size
 *             of the table.
 *      The full expiration check is for this purpose now.
 */
static void ip_vs_lblc_check_expire(unsigned long data)
{
    struct ip_vs_service *svc = (struct ip_vs_service *) data;
    struct ip_vs_lblc_table *tbl = svc->sched_data;
    unsigned long now = jiffies;
    int goal;
    int i, j;
    struct ip_vs_lblc_entry *en, *nxt;

    if ((tbl->counter % COUNT_FOR_FULL_EXPIRATION) == 0) {
        /* do full expiration check */
        ip_vs_lblc_full_check(svc);
        tbl->counter = 1;
        goto out;
    }

    if (atomic_read(&tbl->entries) <= tbl->max_size) {
        tbl->counter++;
        goto out;
    }

    goal = (atomic_read(&tbl->entries) - tbl->max_size)*4/3;
    if (goal > tbl->max_size/2)
        goal = tbl->max_size/2;

    for (i=0, j=tbl->rover; i<IP_VS_LBLC_TAB_SIZE; i++) {
        j = (j + 1) & IP_VS_LBLC_TAB_MASK;

        write_lock(&svc->sched_lock);
        list_for_each_entry_safe(en, nxt, &tbl->bucket[j], list) {
            if (time_before(now, en->lastuse + ENTRY_TIMEOUT))
                continue;

            ip_vs_lblc_free(en);
            atomic_dec(&tbl->entries);
            goal--;
        }
        write_unlock(&svc->sched_lock);
        if (goal <= 0)
            break;
    }
    tbl->rover = j;

  out:
    mod_timer(&tbl->periodic_timer, jiffies+CHECK_EXPIRE_INTERVAL);
}


static int ip_vs_lblc_init_svc(struct ip_vs_service *svc)
{
    int i;
    struct ip_vs_lblc_table *tbl;

    /*
     *    Allocate the ip_vs_lblc_table for this service
     */
    tbl = kmalloc(sizeof(*tbl), GFP_KERNEL);
    if (tbl == NULL)
        return -ENOMEM;

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

    /*
     *    Initialize the hash buckets
     */
    for (i=0; i<IP_VS_LBLC_TAB_SIZE; i++) {
        INIT_LIST_HEAD(&tbl->bucket[i]);
    }
    tbl->max_size = IP_VS_LBLC_TAB_SIZE*16;
    tbl->rover = 0;
    tbl->counter = 1;

    /*
     *    Hook periodic timer for garbage collection
     */
    setup_timer(&tbl->periodic_timer, ip_vs_lblc_check_expire,
            (unsigned long)svc);
    mod_timer(&tbl->periodic_timer, jiffies + CHECK_EXPIRE_INTERVAL);

    return 0;
}


static int ip_vs_lblc_done_svc(struct ip_vs_service *svc)
{
    struct ip_vs_lblc_table *tbl = svc->sched_data;

    /* remove periodic timer */
    del_timer_sync(&tbl->periodic_timer);

    /* got to clean up table entries here */
    ip_vs_lblc_flush(tbl);

    /* release the table itself */
    kfree(tbl);
    IP_VS_DBG(6, "LBLC hash table (memory=%Zdbytes) released\n",
          sizeof(*tbl));

    return 0;
}


static inline struct ip_vs_dest *
__ip_vs_lblc_schedule(struct ip_vs_service *svc)
{
    struct ip_vs_dest *dest, *least;
    int loh, doh;

    /*
     * We use the following formula to estimate the load:
     *                (dest overhead) / dest->weight
     *
     * Remember -- no floats in kernel mode!!!
     * The comparison of h1*w2 > h2*w1 is equivalent to that of
     *                h1/w1 > h2/w2
     * if every weight is larger than zero.
     *
     * The server with weight=0 is quiesced and will not receive any
     * new connection.
     */
    list_for_each_entry(dest, &svc->destinations, n_list) {
        if (dest->flags & IP_VS_DEST_F_OVERLOAD)
            continue;
        if (atomic_read(&dest->weight) > 0) {
            least = dest;
            loh = ip_vs_dest_conn_overhead(least);
            goto nextstage;
        }
    }
    return NULL;

    /*
     *    Find the destination with the least load.
     */
  nextstage:
    list_for_each_entry_continue(dest, &svc->destinations, n_list) {
        if (dest->flags & IP_VS_DEST_F_OVERLOAD)
            continue;

        doh = ip_vs_dest_conn_overhead(dest);
        if (loh * atomic_read(&dest->weight) >
            doh * atomic_read(&least->weight)) {
            least = dest;
            loh = doh;
        }
    }

    IP_VS_DBG_BUF(6, "LBLC: server %s:%d "
              "activeconns %d refcnt %d weight %d overhead %d\n",
              IP_VS_DBG_ADDR(least->af, &least->addr),
              ntohs(least->port),
              atomic_read(&least->activeconns),
              atomic_read(&least->refcnt),
              atomic_read(&least->weight), loh);

    return least;
}


/*
 *   If this destination server is overloaded and there is a less loaded
 *   server, then return true.
 */
static inline int
is_overloaded(struct ip_vs_dest *dest, struct ip_vs_service *svc)
{
    if (atomic_read(&dest->activeconns) > atomic_read(&dest->weight)) {
        struct ip_vs_dest *d;

        list_for_each_entry(d, &svc->destinations, n_list) {
            if (atomic_read(&d->activeconns)*2
                < atomic_read(&d->weight)) {
                return 1;
            }
        }
    }
    return 0;
}


/*
 *    Locality-Based (weighted) Least-Connection scheduling
 */
static struct ip_vs_dest *
ip_vs_lblc_schedule(struct ip_vs_service *svc, const struct sk_buff *skb)
{
    struct ip_vs_lblc_table *tbl = svc->sched_data;
    struct ip_vs_iphdr iph;
    struct ip_vs_dest *dest = NULL;
    struct ip_vs_lblc_entry *en;

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

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

    /* First look in our cache */
    read_lock(&svc->sched_lock);
    en = ip_vs_lblc_get(svc->af, tbl, &iph.daddr);
    if (en) {
        /* We only hold a read lock, but this is atomic */
        en->lastuse = jiffies;

        /*
         * If the destination is not available, i.e. it's in the trash,
         * we must ignore it, as it may be removed from under our feet,
         * if someone drops our reference count. Our caller only makes
         * sure that destinations, that are not in the trash, are not
         * moved to the trash, while we are scheduling. But anyone can
         * free up entries from the trash at any time.
         */

        if (en->dest->flags & IP_VS_DEST_F_AVAILABLE)
            dest = en->dest;
    }
    read_unlock(&svc->sched_lock);

    /* If the destination has a weight and is not overloaded, use it */
    if (dest && atomic_read(&dest->weight) > 0 && !is_overloaded(dest, svc))
        goto out;

    /* No cache entry or it is invalid, time to schedule */
    dest = __ip_vs_lblc_schedule(svc);
    if (!dest) {
        ip_vs_scheduler_err(svc, "no destination available");
        return NULL;
    }

    /* If we fail to create a cache entry, we'll just use the valid dest */
    write_lock(&svc->sched_lock);
    ip_vs_lblc_new(tbl, &iph.daddr, dest);
    write_unlock(&svc->sched_lock);

out:
    IP_VS_DBG_BUF(6, "LBLC: 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 LBLC Scheduler structure
 */
static struct ip_vs_scheduler ip_vs_lblc_scheduler =
{
    .name =         "lblc",
    .refcnt =       ATOMIC_INIT(0),
    .module =       THIS_MODULE,
    .n_list =       LIST_HEAD_INIT(ip_vs_lblc_scheduler.n_list),
    .init_service =     ip_vs_lblc_init_svc,
    .done_service =     ip_vs_lblc_done_svc,
    .schedule =     ip_vs_lblc_schedule,
};

/*
 *  per netns init.
 */
#ifdef CONFIG_SYSCTL
static int __net_init __ip_vs_lblc_init(struct net *net)
{
    struct netns_ipvs *ipvs = net_ipvs(net);

    if (!ipvs)
        return -ENOENT;

    if (!net_eq(net, &init_net)) {
        ipvs->lblc_ctl_table = kmemdup(vs_vars_table,
                        sizeof(vs_vars_table),
                        GFP_KERNEL);
        if (ipvs->lblc_ctl_table == NULL)
            return -ENOMEM;
    } else
        ipvs->lblc_ctl_table = vs_vars_table;
    ipvs->sysctl_lblc_expiration = DEFAULT_EXPIRATION;
    ipvs->lblc_ctl_table[0].data = &ipvs->sysctl_lblc_expiration;

    ipvs->lblc_ctl_header =
        register_net_sysctl(net, "net/ipv4/vs", ipvs->lblc_ctl_table);
    if (!ipvs->lblc_ctl_header) {
        if (!net_eq(net, &init_net))
            kfree(ipvs->lblc_ctl_table);
        return -ENOMEM;
    }

    return 0;
}

static void __net_exit __ip_vs_lblc_exit(struct net *net)
{
    struct netns_ipvs *ipvs = net_ipvs(net);

    unregister_net_sysctl_table(ipvs->lblc_ctl_header);

    if (!net_eq(net, &init_net))
        kfree(ipvs->lblc_ctl_table);
}

#else

static int __net_init __ip_vs_lblc_init(struct net *net) { return 0; }
static void __net_exit __ip_vs_lblc_exit(struct net *net) { }

#endif

static struct pernet_operations ip_vs_lblc_ops = {
    .init = __ip_vs_lblc_init,
    .exit = __ip_vs_lblc_exit,
};

static int __init ip_vs_lblc_init(void)
{
    int ret;

    ret = register_pernet_subsys(&ip_vs_lblc_ops);
    if (ret)
        return ret;

    ret = register_ip_vs_scheduler(&ip_vs_lblc_scheduler);
    if (ret)
        unregister_pernet_subsys(&ip_vs_lblc_ops);
    return ret;
}

static void __exit ip_vs_lblc_cleanup(void)
{
    unregister_ip_vs_scheduler(&ip_vs_lblc_scheduler);
    unregister_pernet_subsys(&ip_vs_lblc_ops);
}


module_init(ip_vs_lblc_init);
module_exit(ip_vs_lblc_cleanup);
MODULE_LICENSE("GPL");