FreeBSD/Linux Kernel Cross Reference
sys/netinet/tcp_hostcache.c

     /*-
      * SPDX-License-Identifier: BSD-3-Clause
      *
      * Copyright (c) 2002 Andre Oppermann, Internet Business Solutions AG
      * All rights reserved.
      *
      * Redistribution and use in source and binary forms, with or without
      * modification, are permitted provided that the following conditions
      * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 3. The name of the author may not be used to endorse or promote
     *    products derived from this software without specific prior written
     *    permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     */
    
    /*
     * The tcp_hostcache moves the tcp-specific cached metrics from the routing
     * table to a dedicated structure indexed by the remote IP address.  It keeps
     * information on the measured TCP parameters of past TCP sessions to allow
     * better initial start values to be used with later connections to/from the
     * same source.  Depending on the network parameters (delay, max MTU,
     * congestion window) between local and remote sites, this can lead to
     * significant speed-ups for new TCP connections after the first one.
     *
     * Due to the tcp_hostcache, all TCP-specific metrics information in the
     * routing table have been removed.  The inpcb no longer keeps a pointer to
     * the routing entry, and protocol-initiated route cloning has been removed
     * as well.  With these changes, the routing table has gone back to being
     * more lightwight and only carries information related to packet forwarding.
     *
     * tcp_hostcache is designed for multiple concurrent access in SMP
     * environments and high contention.  All bucket rows have their own lock and
     * thus multiple lookups and modifies can be done at the same time as long as
     * they are in different bucket rows.  If a request for insertion of a new
     * record can't be satisfied, it simply returns an empty structure.  Nobody
     * and nothing outside of tcp_hostcache.c will ever point directly to any
     * entry in the tcp_hostcache.  All communication is done in an
     * object-oriented way and only functions of tcp_hostcache will manipulate
     * hostcache entries.  Otherwise, we are unable to achieve good behaviour in
     * concurrent access situations.  Since tcp_hostcache is only caching
     * information, there are no fatal consequences if we either can't satisfy
     * any particular request or have to drop/overwrite an existing entry because
     * of bucket limit memory constrains.
     */
    
    /*
     * Many thanks to jlemon for basic structure of tcp_syncache which is being
     * followed here.
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD$");
    
    #include "opt_inet6.h"
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/jail.h>
    #include <sys/kernel.h>
    #include <sys/lock.h>
    #include <sys/mutex.h>
    #include <sys/malloc.h>
    #include <sys/proc.h>
    #include <sys/sbuf.h>
    #include <sys/socket.h>
    #include <sys/socketvar.h>
    #include <sys/sysctl.h>
    
    #include <net/if.h>
    #include <net/if_var.h>
    #include <net/route.h>
    #include <net/vnet.h>
    
    #include <netinet/in.h>
    #include <netinet/in_systm.h>
    #include <netinet/ip.h>
    #include <netinet/in_var.h>
    #include <netinet/in_pcb.h>
    #include <netinet/ip_var.h>
    #ifdef INET6
    #include <netinet/ip6.h>
    #include <netinet6/ip6_var.h>
    #endif
   #include <netinet/tcp.h>
   #include <netinet/tcp_var.h>
   #include <netinet/tcp_hostcache.h>
   #ifdef INET6
   #include <netinet6/tcp6_var.h>
   #endif
   
   #include <vm/uma.h>
   
   /* Arbitrary values */
   #define TCP_HOSTCACHE_HASHSIZE          512
   #define TCP_HOSTCACHE_BUCKETLIMIT       30
   #define TCP_HOSTCACHE_EXPIRE            60*60   /* one hour */
   #define TCP_HOSTCACHE_PRUNE             5*60    /* every 5 minutes */
   
   VNET_DEFINE_STATIC(struct tcp_hostcache, tcp_hostcache);
   #define V_tcp_hostcache         VNET(tcp_hostcache)
   
   VNET_DEFINE_STATIC(struct callout, tcp_hc_callout);
   #define V_tcp_hc_callout        VNET(tcp_hc_callout)
   
   static struct hc_metrics *tcp_hc_lookup(struct in_conninfo *);
   static struct hc_metrics *tcp_hc_insert(struct in_conninfo *);
   static int sysctl_tcp_hc_list(SYSCTL_HANDLER_ARGS);
   static int sysctl_tcp_hc_purgenow(SYSCTL_HANDLER_ARGS);
   static void tcp_hc_purge_internal(int);
   static void tcp_hc_purge(void *);
   
   static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, hostcache, CTLFLAG_RW, 0,
       "TCP Host cache");
   
   VNET_DEFINE(int, tcp_use_hostcache) = 1;
   #define V_tcp_use_hostcache  VNET(tcp_use_hostcache)
   SYSCTL_INT(_net_inet_tcp_hostcache, OID_AUTO, enable, CTLFLAG_VNET | CTLFLAG_RW,
       &VNET_NAME(tcp_use_hostcache), 0,
       "Enable the TCP hostcache");
   
   SYSCTL_UINT(_net_inet_tcp_hostcache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
       &VNET_NAME(tcp_hostcache.cache_limit), 0,
       "Overall entry limit for hostcache");
   
   SYSCTL_UINT(_net_inet_tcp_hostcache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN,
       &VNET_NAME(tcp_hostcache.hashsize), 0,
       "Size of TCP hostcache hashtable");
   
   SYSCTL_UINT(_net_inet_tcp_hostcache, OID_AUTO, bucketlimit,
       CTLFLAG_VNET | CTLFLAG_RDTUN, &VNET_NAME(tcp_hostcache.bucket_limit), 0,
       "Per-bucket hash limit for hostcache");
   
   SYSCTL_UINT(_net_inet_tcp_hostcache, OID_AUTO, count, CTLFLAG_VNET | CTLFLAG_RD,
        &VNET_NAME(tcp_hostcache.cache_count), 0,
       "Current number of entries in hostcache");
   
   SYSCTL_INT(_net_inet_tcp_hostcache, OID_AUTO, expire, CTLFLAG_VNET | CTLFLAG_RW,
       &VNET_NAME(tcp_hostcache.expire), 0,
       "Expire time of TCP hostcache entries");
   
   SYSCTL_INT(_net_inet_tcp_hostcache, OID_AUTO, prune, CTLFLAG_VNET | CTLFLAG_RW,
       &VNET_NAME(tcp_hostcache.prune), 0,
       "Time between purge runs");
   
   SYSCTL_INT(_net_inet_tcp_hostcache, OID_AUTO, purge, CTLFLAG_VNET | CTLFLAG_RW,
       &VNET_NAME(tcp_hostcache.purgeall), 0,
       "Expire all entries on next purge run");
   
   SYSCTL_PROC(_net_inet_tcp_hostcache, OID_AUTO, list,
       CTLTYPE_STRING | CTLFLAG_RD | CTLFLAG_SKIP, 0, 0,
       sysctl_tcp_hc_list, "A", "List of all hostcache entries");
   
   SYSCTL_PROC(_net_inet_tcp_hostcache, OID_AUTO, purgenow,
       CTLTYPE_INT | CTLFLAG_RW, NULL, 0,
       sysctl_tcp_hc_purgenow, "I", "Immediately purge all entries");
   
   static MALLOC_DEFINE(M_HOSTCACHE, "hostcache", "TCP hostcache");
   
   #define HOSTCACHE_HASH(ip) \
           (((ip)->s_addr ^ ((ip)->s_addr >> 7) ^ ((ip)->s_addr >> 17)) &  \
             V_tcp_hostcache.hashmask)
   
   /* XXX: What is the recommended hash to get good entropy for IPv6 addresses? */
   #define HOSTCACHE_HASH6(ip6)                            \
           (((ip6)->s6_addr32[0] ^                         \
             (ip6)->s6_addr32[1] ^                         \
             (ip6)->s6_addr32[2] ^                         \
             (ip6)->s6_addr32[3]) &                        \
            V_tcp_hostcache.hashmask)
   
   #define THC_LOCK(lp)            mtx_lock(lp)
   #define THC_UNLOCK(lp)          mtx_unlock(lp)
   
   void
   tcp_hc_init(void)
   {
           u_int cache_limit;
           int i;
   
           /*
            * Initialize hostcache structures.
            */
           atomic_store_int(&V_tcp_hostcache.cache_count, 0);
           V_tcp_hostcache.hashsize = TCP_HOSTCACHE_HASHSIZE;
           V_tcp_hostcache.bucket_limit = TCP_HOSTCACHE_BUCKETLIMIT;
           V_tcp_hostcache.expire = TCP_HOSTCACHE_EXPIRE;
           V_tcp_hostcache.prune = TCP_HOSTCACHE_PRUNE;
   
           TUNABLE_INT_FETCH("net.inet.tcp.hostcache.hashsize",
               &V_tcp_hostcache.hashsize);
           if (!powerof2(V_tcp_hostcache.hashsize)) {
                   printf("WARNING: hostcache hash size is not a power of 2.\n");
                   V_tcp_hostcache.hashsize = TCP_HOSTCACHE_HASHSIZE; /* default */
           }
           V_tcp_hostcache.hashmask = V_tcp_hostcache.hashsize - 1;
   
           TUNABLE_INT_FETCH("net.inet.tcp.hostcache.bucketlimit",
               &V_tcp_hostcache.bucket_limit);
   
           cache_limit = V_tcp_hostcache.hashsize * V_tcp_hostcache.bucket_limit;
           V_tcp_hostcache.cache_limit = cache_limit;
           TUNABLE_INT_FETCH("net.inet.tcp.hostcache.cachelimit",
               &V_tcp_hostcache.cache_limit);
           if (V_tcp_hostcache.cache_limit > cache_limit)
                   V_tcp_hostcache.cache_limit = cache_limit;
   
           /*
            * Allocate the hash table.
            */
           V_tcp_hostcache.hashbase = (struct hc_head *)
               malloc(V_tcp_hostcache.hashsize * sizeof(struct hc_head),
                      M_HOSTCACHE, M_WAITOK | M_ZERO);
   
           /*
            * Initialize the hash buckets.
            */
           for (i = 0; i < V_tcp_hostcache.hashsize; i++) {
                   TAILQ_INIT(&V_tcp_hostcache.hashbase[i].hch_bucket);
                   V_tcp_hostcache.hashbase[i].hch_length = 0;
                   mtx_init(&V_tcp_hostcache.hashbase[i].hch_mtx, "tcp_hc_entry",
                             NULL, MTX_DEF);
           }
   
           /*
            * Allocate the hostcache entries.
            */
           V_tcp_hostcache.zone =
               uma_zcreate("hostcache", sizeof(struct hc_metrics),
               NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
           uma_zone_set_max(V_tcp_hostcache.zone, V_tcp_hostcache.cache_limit);
   
           /*
            * Set up periodic cache cleanup.
            */
           callout_init(&V_tcp_hc_callout, 1);
           callout_reset(&V_tcp_hc_callout, V_tcp_hostcache.prune * hz,
               tcp_hc_purge, curvnet);
   }
   
   #ifdef VIMAGE
   void
   tcp_hc_destroy(void)
   {
           int i;
   
           callout_drain(&V_tcp_hc_callout);
   
           /* Purge all hc entries. */
           tcp_hc_purge_internal(1);
   
           /* Free the uma zone and the allocated hash table. */
           uma_zdestroy(V_tcp_hostcache.zone);
   
           for (i = 0; i < V_tcp_hostcache.hashsize; i++)
                   mtx_destroy(&V_tcp_hostcache.hashbase[i].hch_mtx);
           free(V_tcp_hostcache.hashbase, M_HOSTCACHE);
   }
   #endif
   
   /*
    * Internal function: look up an entry in the hostcache or return NULL.
    *
    * If an entry has been returned, the caller becomes responsible for
    * unlocking the bucket row after he is done reading/modifying the entry.
    */
   static struct hc_metrics *
   tcp_hc_lookup(struct in_conninfo *inc)
   {
           int hash;
           struct hc_head *hc_head;
           struct hc_metrics *hc_entry;
   
           if (!V_tcp_use_hostcache)
                   return NULL;
   
           KASSERT(inc != NULL, ("tcp_hc_lookup with NULL in_conninfo pointer"));
   
           /*
            * Hash the foreign ip address.
            */
           if (inc->inc_flags & INC_ISIPV6)
                   hash = HOSTCACHE_HASH6(&inc->inc6_faddr);
           else
                   hash = HOSTCACHE_HASH(&inc->inc_faddr);
   
           hc_head = &V_tcp_hostcache.hashbase[hash];
   
           /*
            * Acquire lock for this bucket row; we release the lock if we don't
            * find an entry, otherwise the caller has to unlock after he is
            * done.
            */
           THC_LOCK(&hc_head->hch_mtx);
   
           /*
            * Iterate through entries in bucket row looking for a match.
            */
           TAILQ_FOREACH(hc_entry, &hc_head->hch_bucket, rmx_q) {
                   if (inc->inc_flags & INC_ISIPV6) {
                           /* XXX: check ip6_zoneid */
                           if (memcmp(&inc->inc6_faddr, &hc_entry->ip6,
                               sizeof(inc->inc6_faddr)) == 0)
                                   return hc_entry;
                   } else {
                           if (memcmp(&inc->inc_faddr, &hc_entry->ip4,
                               sizeof(inc->inc_faddr)) == 0)
                                   return hc_entry;
                   }
           }
   
           /*
            * We were unsuccessful and didn't find anything.
            */
           THC_UNLOCK(&hc_head->hch_mtx);
           return NULL;
   }
   
   /*
    * Internal function: insert an entry into the hostcache or return NULL if
    * unable to allocate a new one.
    *
    * If an entry has been returned, the caller becomes responsible for
    * unlocking the bucket row after he is done reading/modifying the entry.
    */
   static struct hc_metrics *
   tcp_hc_insert(struct in_conninfo *inc)
   {
           int hash;
           struct hc_head *hc_head;
           struct hc_metrics *hc_entry;
   
           if (!V_tcp_use_hostcache)
                   return NULL;
   
           KASSERT(inc != NULL, ("tcp_hc_insert with NULL in_conninfo pointer"));
   
           /*
            * Hash the foreign ip address.
            */
           if (inc->inc_flags & INC_ISIPV6)
                   hash = HOSTCACHE_HASH6(&inc->inc6_faddr);
           else
                   hash = HOSTCACHE_HASH(&inc->inc_faddr);
   
           hc_head = &V_tcp_hostcache.hashbase[hash];
   
           /*
            * Acquire lock for this bucket row; we release the lock if we don't
            * find an entry, otherwise the caller has to unlock after he is
            * done.
            */
           THC_LOCK(&hc_head->hch_mtx);
   
           /*
            * If the bucket limit is reached, reuse the least-used element.
            */
           if (hc_head->hch_length >= V_tcp_hostcache.bucket_limit ||
               atomic_load_int(&V_tcp_hostcache.cache_count) >= V_tcp_hostcache.cache_limit) {
                   hc_entry = TAILQ_LAST(&hc_head->hch_bucket, hc_qhead);
                   /*
                    * At first we were dropping the last element, just to
                    * reacquire it in the next two lines again, which isn't very
                    * efficient.  Instead just reuse the least used element.
                    * We may drop something that is still "in-use" but we can be
                    * "lossy".
                    * Just give up if this bucket row is empty and we don't have
                    * anything to replace.
                    */
                   if (hc_entry == NULL) {
                           THC_UNLOCK(&hc_head->hch_mtx);
                           return NULL;
                   }
                   TAILQ_REMOVE(&hc_head->hch_bucket, hc_entry, rmx_q);
                   V_tcp_hostcache.hashbase[hash].hch_length--;
                   atomic_subtract_int(&V_tcp_hostcache.cache_count, 1);
                   TCPSTAT_INC(tcps_hc_bucketoverflow);
   #if 0
                   uma_zfree(V_tcp_hostcache.zone, hc_entry);
   #endif
           } else {
                   /*
                    * Allocate a new entry, or balk if not possible.
                    */
                   hc_entry = uma_zalloc(V_tcp_hostcache.zone, M_NOWAIT);
                   if (hc_entry == NULL) {
                           THC_UNLOCK(&hc_head->hch_mtx);
                           return NULL;
                   }
           }
   
           /*
            * Initialize basic information of hostcache entry.
            */
           bzero(hc_entry, sizeof(*hc_entry));
           if (inc->inc_flags & INC_ISIPV6) {
                   hc_entry->ip6 = inc->inc6_faddr;
                   hc_entry->ip6_zoneid = inc->inc6_zoneid;
           } else
                   hc_entry->ip4 = inc->inc_faddr;
           hc_entry->rmx_head = hc_head;
           hc_entry->rmx_expire = V_tcp_hostcache.expire;
   
           /*
            * Put it upfront.
            */
           TAILQ_INSERT_HEAD(&hc_head->hch_bucket, hc_entry, rmx_q);
           V_tcp_hostcache.hashbase[hash].hch_length++;
           atomic_add_int(&V_tcp_hostcache.cache_count, 1);
           TCPSTAT_INC(tcps_hc_added);
   
           return hc_entry;
   }
   
   /*
    * External function: look up an entry in the hostcache and fill out the
    * supplied TCP metrics structure.  Fills in NULL when no entry was found or
    * a value is not set.
    */
   void
   tcp_hc_get(struct in_conninfo *inc, struct hc_metrics_lite *hc_metrics_lite)
   {
           struct hc_metrics *hc_entry;
   
           if (!V_tcp_use_hostcache) {
                   bzero(hc_metrics_lite, sizeof(*hc_metrics_lite));
                   return;
           }
   
           /*
            * Find the right bucket.
            */
           hc_entry = tcp_hc_lookup(inc);
   
           /*
            * If we don't have an existing object.
            */
           if (hc_entry == NULL) {
                   bzero(hc_metrics_lite, sizeof(*hc_metrics_lite));
                   return;
           }
           hc_entry->rmx_hits++;
           hc_entry->rmx_expire = V_tcp_hostcache.expire; /* start over again */
   
           hc_metrics_lite->rmx_mtu = hc_entry->rmx_mtu;
           hc_metrics_lite->rmx_ssthresh = hc_entry->rmx_ssthresh;
           hc_metrics_lite->rmx_rtt = hc_entry->rmx_rtt;
           hc_metrics_lite->rmx_rttvar = hc_entry->rmx_rttvar;
           hc_metrics_lite->rmx_cwnd = hc_entry->rmx_cwnd;
           hc_metrics_lite->rmx_sendpipe = hc_entry->rmx_sendpipe;
           hc_metrics_lite->rmx_recvpipe = hc_entry->rmx_recvpipe;
   
           /*
            * Unlock bucket row.
            */
           THC_UNLOCK(&hc_entry->rmx_head->hch_mtx);
   }
   
   /*
    * External function: look up an entry in the hostcache and return the
    * discovered path MTU.  Returns 0 if no entry is found or value is not
    * set.
    */
   uint32_t
   tcp_hc_getmtu(struct in_conninfo *inc)
   {
           struct hc_metrics *hc_entry;
           uint32_t mtu;
   
           if (!V_tcp_use_hostcache)
                   return 0;
   
           hc_entry = tcp_hc_lookup(inc);
           if (hc_entry == NULL) {
                   return 0;
           }
           hc_entry->rmx_hits++;
           hc_entry->rmx_expire = V_tcp_hostcache.expire; /* start over again */
   
           mtu = hc_entry->rmx_mtu;
           THC_UNLOCK(&hc_entry->rmx_head->hch_mtx);
           return mtu;
   }
   
   /*
    * External function: update the MTU value of an entry in the hostcache.
    * Creates a new entry if none was found.
    */
   void
   tcp_hc_updatemtu(struct in_conninfo *inc, uint32_t mtu)
   {
           struct hc_metrics *hc_entry;
   
           if (!V_tcp_use_hostcache)
                   return;
   
           /*
            * Find the right bucket.
            */
           hc_entry = tcp_hc_lookup(inc);
   
           /*
            * If we don't have an existing object, try to insert a new one.
            */
           if (hc_entry == NULL) {
                   hc_entry = tcp_hc_insert(inc);
                   if (hc_entry == NULL)
                           return;
           }
           hc_entry->rmx_updates++;
           hc_entry->rmx_expire = V_tcp_hostcache.expire; /* start over again */
   
           hc_entry->rmx_mtu = mtu;
   
           /*
            * Put it upfront so we find it faster next time.
            */
           TAILQ_REMOVE(&hc_entry->rmx_head->hch_bucket, hc_entry, rmx_q);
           TAILQ_INSERT_HEAD(&hc_entry->rmx_head->hch_bucket, hc_entry, rmx_q);
   
           /*
            * Unlock bucket row.
            */
           THC_UNLOCK(&hc_entry->rmx_head->hch_mtx);
   }
   
   /*
    * External function: update the TCP metrics of an entry in the hostcache.
    * Creates a new entry if none was found.
    */
   void
   tcp_hc_update(struct in_conninfo *inc, struct hc_metrics_lite *hcml)
   {
           struct hc_metrics *hc_entry;
   
           if (!V_tcp_use_hostcache)
                   return;
   
           hc_entry = tcp_hc_lookup(inc);
           if (hc_entry == NULL) {
                   hc_entry = tcp_hc_insert(inc);
                   if (hc_entry == NULL)
                           return;
           }
           hc_entry->rmx_updates++;
           hc_entry->rmx_expire = V_tcp_hostcache.expire; /* start over again */
   
           if (hcml->rmx_rtt != 0) {
                   if (hc_entry->rmx_rtt == 0)
                           hc_entry->rmx_rtt = hcml->rmx_rtt;
                   else
                           hc_entry->rmx_rtt = ((uint64_t)hc_entry->rmx_rtt +
                               (uint64_t)hcml->rmx_rtt) / 2;
                   TCPSTAT_INC(tcps_cachedrtt);
           }
           if (hcml->rmx_rttvar != 0) {
                   if (hc_entry->rmx_rttvar == 0)
                           hc_entry->rmx_rttvar = hcml->rmx_rttvar;
                   else
                           hc_entry->rmx_rttvar = ((uint64_t)hc_entry->rmx_rttvar +
                               (uint64_t)hcml->rmx_rttvar) / 2;
                   TCPSTAT_INC(tcps_cachedrttvar);
           }
           if (hcml->rmx_ssthresh != 0) {
                   if (hc_entry->rmx_ssthresh == 0)
                           hc_entry->rmx_ssthresh = hcml->rmx_ssthresh;
                   else
                           hc_entry->rmx_ssthresh =
                               (hc_entry->rmx_ssthresh + hcml->rmx_ssthresh) / 2;
                   TCPSTAT_INC(tcps_cachedssthresh);
           }
           if (hcml->rmx_cwnd != 0) {
                   if (hc_entry->rmx_cwnd == 0)
                           hc_entry->rmx_cwnd = hcml->rmx_cwnd;
                   else
                           hc_entry->rmx_cwnd = ((uint64_t)hc_entry->rmx_cwnd +
                               (uint64_t)hcml->rmx_cwnd) / 2;
                   /* TCPSTAT_INC(tcps_cachedcwnd); */
           }
           if (hcml->rmx_sendpipe != 0) {
                   if (hc_entry->rmx_sendpipe == 0)
                           hc_entry->rmx_sendpipe = hcml->rmx_sendpipe;
                   else
                           hc_entry->rmx_sendpipe =
                               ((uint64_t)hc_entry->rmx_sendpipe +
                               (uint64_t)hcml->rmx_sendpipe) /2;
                   /* TCPSTAT_INC(tcps_cachedsendpipe); */
           }
           if (hcml->rmx_recvpipe != 0) {
                   if (hc_entry->rmx_recvpipe == 0)
                           hc_entry->rmx_recvpipe = hcml->rmx_recvpipe;
                   else
                           hc_entry->rmx_recvpipe =
                               ((uint64_t)hc_entry->rmx_recvpipe +
                               (uint64_t)hcml->rmx_recvpipe) /2;
                   /* TCPSTAT_INC(tcps_cachedrecvpipe); */
           }
   
           TAILQ_REMOVE(&hc_entry->rmx_head->hch_bucket, hc_entry, rmx_q);
           TAILQ_INSERT_HEAD(&hc_entry->rmx_head->hch_bucket, hc_entry, rmx_q);
           THC_UNLOCK(&hc_entry->rmx_head->hch_mtx);
   }
   
   /*
    * Sysctl function: prints the list and values of all hostcache entries in
    * unsorted order.
    */
   static int
   sysctl_tcp_hc_list(SYSCTL_HANDLER_ARGS)
   {
           const int linesize = 128;
           struct sbuf sb;
           int i, error, len;
           struct hc_metrics *hc_entry;
           char ip4buf[INET_ADDRSTRLEN];
   #ifdef INET6
           char ip6buf[INET6_ADDRSTRLEN];
   #endif
   
           if (jailed_without_vnet(curthread->td_ucred) != 0)
                   return (EPERM);
   
           /* Optimize Buffer length query by sbin/sysctl */
           if (req->oldptr == NULL) {
                   len = (atomic_load_int(&V_tcp_hostcache.cache_count) + 1) *
                           linesize;
                   return (SYSCTL_OUT(req, NULL, len));
           }
   
           error = sysctl_wire_old_buffer(req, 0);
           if (error != 0) {
                   return(error);
           }
   
           /* Use a buffer sized for one full bucket */
           sbuf_new_for_sysctl(&sb, NULL, V_tcp_hostcache.bucket_limit *
                   linesize, req);
   
           sbuf_printf(&sb,
                   "\nIP address        MTU  SSTRESH      RTT   RTTVAR "
                   "    CWND SENDPIPE RECVPIPE HITS  UPD  EXP\n");
           sbuf_drain(&sb);
   
   #define msec(u) (((u) + 500) / 1000)
           for (i = 0; i < V_tcp_hostcache.hashsize; i++) {
                   THC_LOCK(&V_tcp_hostcache.hashbase[i].hch_mtx);
                   TAILQ_FOREACH(hc_entry, &V_tcp_hostcache.hashbase[i].hch_bucket,
                                 rmx_q) {
                           sbuf_printf(&sb,
                               "%-15s %5u %8u %6lums %6lums %8u %8u %8u %4lu "
                               "%4lu %4i\n",
                               hc_entry->ip4.s_addr ?
                                   inet_ntoa_r(hc_entry->ip4, ip4buf) :
   #ifdef INET6
                                   ip6_sprintf(ip6buf, &hc_entry->ip6),
   #else
                                   "IPv6?",
   #endif
                               hc_entry->rmx_mtu,
                               hc_entry->rmx_ssthresh,
                               msec((u_long)hc_entry->rmx_rtt *
                                   (RTM_RTTUNIT / (hz * TCP_RTT_SCALE))),
                               msec((u_long)hc_entry->rmx_rttvar *
                                   (RTM_RTTUNIT / (hz * TCP_RTTVAR_SCALE))),
                               hc_entry->rmx_cwnd,
                               hc_entry->rmx_sendpipe,
                               hc_entry->rmx_recvpipe,
                               hc_entry->rmx_hits,
                               hc_entry->rmx_updates,
                               hc_entry->rmx_expire);
                   }
                   THC_UNLOCK(&V_tcp_hostcache.hashbase[i].hch_mtx);
                   sbuf_drain(&sb);
           }
   #undef msec
           error = sbuf_finish(&sb);
           sbuf_delete(&sb);
           return(error);
   }
   
   /*
    * Caller has to make sure the curvnet is set properly.
    */
   static void
   tcp_hc_purge_internal(int all)
   {
           struct hc_metrics *hc_entry, *hc_next;
           int i;
   
           for (i = 0; i < V_tcp_hostcache.hashsize; i++) {
                   THC_LOCK(&V_tcp_hostcache.hashbase[i].hch_mtx);
                   TAILQ_FOREACH_SAFE(hc_entry,
                       &V_tcp_hostcache.hashbase[i].hch_bucket, rmx_q, hc_next) {
                           if (all || hc_entry->rmx_expire <= 0) {
                                   TAILQ_REMOVE(&V_tcp_hostcache.hashbase[i].hch_bucket,
                                                 hc_entry, rmx_q);
                                   uma_zfree(V_tcp_hostcache.zone, hc_entry);
                                   V_tcp_hostcache.hashbase[i].hch_length--;
                                   atomic_subtract_int(&V_tcp_hostcache.cache_count, 1);
                           } else
                                   hc_entry->rmx_expire -= V_tcp_hostcache.prune;
                   }
                   THC_UNLOCK(&V_tcp_hostcache.hashbase[i].hch_mtx);
           }
   }
   
   /*
    * Expire and purge (old|all) entries in the tcp_hostcache.  Runs
    * periodically from the callout.
    */
   static void
   tcp_hc_purge(void *arg)
   {
           CURVNET_SET((struct vnet *) arg);
           int all = 0;
   
           if (V_tcp_hostcache.purgeall) {
                   all = 1;
                   V_tcp_hostcache.purgeall = 0;
           }
   
           tcp_hc_purge_internal(all);
   
           callout_reset(&V_tcp_hc_callout, V_tcp_hostcache.prune * hz,
               tcp_hc_purge, arg);
           CURVNET_RESTORE();
   }
   
   /*
    * Expire and purge all entries in hostcache immediately.
    */
   static int
   sysctl_tcp_hc_purgenow(SYSCTL_HANDLER_ARGS)
   {
           int error, val;
   
           val = 0;
           error = sysctl_handle_int(oidp, &val, 0, req);
           if (error || !req->newptr)
                   return (error);
   
           tcp_hc_purge_internal(1);
   
           callout_reset(&V_tcp_hc_callout, V_tcp_hostcache.prune * hz,
               tcp_hc_purge, curvnet);
   
           return (0);
   }

Cache object: 086b367c238b144c14042706e210fb46