GNU Linux-libre 4.14.290-gnu1

[releases.git] / drivers / staging / lustre / lnet / libcfs / hash.c

/*
 * GPL HEADER START
 *
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 only,
 * as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License version 2 for more details (a copy is included
 * in the LICENSE file that accompanied this code).
 *
 * You should have received a copy of the GNU General Public License
 * version 2 along with this program; If not, see
 * http://www.gnu.org/licenses/gpl-2.0.html
 *
 * GPL HEADER END
 */
/*
 * Copyright (c) 2009, 2010, Oracle and/or its affiliates. All rights reserved.
 * Use is subject to license terms.
 *
 * Copyright (c) 2011, 2012, Intel Corporation.
 */
/*
 * This file is part of Lustre, http://www.lustre.org/
 * Lustre is a trademark of Sun Microsystems, Inc.
 *
 * libcfs/libcfs/hash.c
 *
 * Implement a hash class for hash process in lustre system.
 *
 * Author: YuZhangyong <yzy@clusterfs.com>
 *
 * 2008-08-15: Brian Behlendorf <behlendorf1@llnl.gov>
 * - Simplified API and improved documentation
 * - Added per-hash feature flags:
 *   * CFS_HASH_DEBUG additional validation
 *   * CFS_HASH_REHASH dynamic rehashing
 * - Added per-hash statistics
 * - General performance enhancements
 *
 * 2009-07-31: Liang Zhen <zhen.liang@sun.com>
 * - move all stuff to libcfs
 * - don't allow cur_bits != max_bits without setting of CFS_HASH_REHASH
 * - ignore hs_rwlock if without CFS_HASH_REHASH setting
 * - buckets are allocated one by one(instead of contiguous memory),
 *   to avoid unnecessary cacheline conflict
 *
 * 2010-03-01: Liang Zhen <zhen.liang@sun.com>
 * - "bucket" is a group of hlist_head now, user can specify bucket size
 *   by bkt_bits of cfs_hash_create(), all hlist_heads in a bucket share
 *   one lock for reducing memory overhead.
 *
 * - support lockless hash, caller will take care of locks:
 *   avoid lock overhead for hash tables that are already protected
 *   by locking in the caller for another reason
 *
 * - support both spin_lock/rwlock for bucket:
 *   overhead of spinlock contention is lower than read/write
 *   contention of rwlock, so using spinlock to serialize operations on
 *   bucket is more reasonable for those frequently changed hash tables
 *
 * - support one-single lock mode:
 *   one lock to protect all hash operations to avoid overhead of
 *   multiple locks if hash table is always small
 *
 * - removed a lot of unnecessary addref & decref on hash element:
 *   addref & decref are atomic operations in many use-cases which
 *   are expensive.
 *
 * - support non-blocking cfs_hash_add() and cfs_hash_findadd():
 *   some lustre use-cases require these functions to be strictly
 *   non-blocking, we need to schedule required rehash on a different
 *   thread on those cases.
 *
 * - safer rehash on large hash table
 *   In old implementation, rehash function will exclusively lock the
 *   hash table and finish rehash in one batch, it's dangerous on SMP
 *   system because rehash millions of elements could take long time.
 *   New implemented rehash can release lock and relax CPU in middle
 *   of rehash, it's safe for another thread to search/change on the
 *   hash table even it's in rehasing.
 *
 * - support two different refcount modes
 *   . hash table has refcount on element
 *   . hash table doesn't change refcount on adding/removing element
 *
 * - support long name hash table (for param-tree)
 *
 * - fix a bug for cfs_hash_rehash_key:
 *   in old implementation, cfs_hash_rehash_key could screw up the
 *   hash-table because @key is overwritten without any protection.
 *   Now we need user to define hs_keycpy for those rehash enabled
 *   hash tables, cfs_hash_rehash_key will overwrite hash-key
 *   inside lock by calling hs_keycpy.
 *
 * - better hash iteration:
 *   Now we support both locked iteration & lockless iteration of hash
 *   table. Also, user can break the iteration by return 1 in callback.
 */
#include <linux/seq_file.h>
#include <linux/log2.h>

#include <linux/libcfs/libcfs.h>

#if CFS_HASH_DEBUG_LEVEL >= CFS_HASH_DEBUG_1
static unsigned int warn_on_depth = 8;
module_param(warn_on_depth, uint, 0644);
MODULE_PARM_DESC(warn_on_depth, "warning when hash depth is high.");
#endif

struct cfs_wi_sched *cfs_sched_rehash;

static inline void
cfs_hash_nl_lock(union cfs_hash_lock *lock, int exclusive) {}

static inline void
cfs_hash_nl_unlock(union cfs_hash_lock *lock, int exclusive) {}

static inline void
cfs_hash_spin_lock(union cfs_hash_lock *lock, int exclusive)
        __acquires(&lock->spin)
{
        spin_lock(&lock->spin);
}

static inline void
cfs_hash_spin_unlock(union cfs_hash_lock *lock, int exclusive)
        __releases(&lock->spin)
{
        spin_unlock(&lock->spin);
}

static inline void
cfs_hash_rw_lock(union cfs_hash_lock *lock, int exclusive)
        __acquires(&lock->rw)
{
        if (!exclusive)
                read_lock(&lock->rw);
        else
                write_lock(&lock->rw);
}

static inline void
cfs_hash_rw_unlock(union cfs_hash_lock *lock, int exclusive)
        __releases(&lock->rw)
{
        if (!exclusive)
                read_unlock(&lock->rw);
        else
                write_unlock(&lock->rw);
}

/** No lock hash */
static struct cfs_hash_lock_ops cfs_hash_nl_lops = {
        .hs_lock        = cfs_hash_nl_lock,
        .hs_unlock      = cfs_hash_nl_unlock,
        .hs_bkt_lock    = cfs_hash_nl_lock,
        .hs_bkt_unlock  = cfs_hash_nl_unlock,
};

/** no bucket lock, one spinlock to protect everything */
static struct cfs_hash_lock_ops cfs_hash_nbl_lops = {
        .hs_lock        = cfs_hash_spin_lock,
        .hs_unlock      = cfs_hash_spin_unlock,
        .hs_bkt_lock    = cfs_hash_nl_lock,
        .hs_bkt_unlock  = cfs_hash_nl_unlock,
};

/** spin bucket lock, rehash is enabled */
static struct cfs_hash_lock_ops cfs_hash_bkt_spin_lops = {
        .hs_lock        = cfs_hash_rw_lock,
        .hs_unlock      = cfs_hash_rw_unlock,
        .hs_bkt_lock    = cfs_hash_spin_lock,
        .hs_bkt_unlock  = cfs_hash_spin_unlock,
};

/** rw bucket lock, rehash is enabled */
static struct cfs_hash_lock_ops cfs_hash_bkt_rw_lops = {
        .hs_lock        = cfs_hash_rw_lock,
        .hs_unlock      = cfs_hash_rw_unlock,
        .hs_bkt_lock    = cfs_hash_rw_lock,
        .hs_bkt_unlock  = cfs_hash_rw_unlock,
};

/** spin bucket lock, rehash is disabled */
static struct cfs_hash_lock_ops cfs_hash_nr_bkt_spin_lops = {
        .hs_lock        = cfs_hash_nl_lock,
        .hs_unlock      = cfs_hash_nl_unlock,
        .hs_bkt_lock    = cfs_hash_spin_lock,
        .hs_bkt_unlock  = cfs_hash_spin_unlock,
};

/** rw bucket lock, rehash is disabled */
static struct cfs_hash_lock_ops cfs_hash_nr_bkt_rw_lops = {
        .hs_lock        = cfs_hash_nl_lock,
        .hs_unlock      = cfs_hash_nl_unlock,
        .hs_bkt_lock    = cfs_hash_rw_lock,
        .hs_bkt_unlock  = cfs_hash_rw_unlock,
};

static void
cfs_hash_lock_setup(struct cfs_hash *hs)
{
        if (cfs_hash_with_no_lock(hs)) {
                hs->hs_lops = &cfs_hash_nl_lops;

        } else if (cfs_hash_with_no_bktlock(hs)) {
                hs->hs_lops = &cfs_hash_nbl_lops;
                spin_lock_init(&hs->hs_lock.spin);

        } else if (cfs_hash_with_rehash(hs)) {
                rwlock_init(&hs->hs_lock.rw);

                if (cfs_hash_with_rw_bktlock(hs))
                        hs->hs_lops = &cfs_hash_bkt_rw_lops;
                else if (cfs_hash_with_spin_bktlock(hs))
                        hs->hs_lops = &cfs_hash_bkt_spin_lops;
                else
                        LBUG();
        } else {
                if (cfs_hash_with_rw_bktlock(hs))
                        hs->hs_lops = &cfs_hash_nr_bkt_rw_lops;
                else if (cfs_hash_with_spin_bktlock(hs))
                        hs->hs_lops = &cfs_hash_nr_bkt_spin_lops;
                else
                        LBUG();
        }
}

/**
 * Simple hash head without depth tracking
 * new element is always added to head of hlist
 */
struct cfs_hash_head {
        struct hlist_head       hh_head;        /**< entries list */
};

static int
cfs_hash_hh_hhead_size(struct cfs_hash *hs)
{
        return sizeof(struct cfs_hash_head);
}

static struct hlist_head *
cfs_hash_hh_hhead(struct cfs_hash *hs, struct cfs_hash_bd *bd)
{
        struct cfs_hash_head *head;

        head = (struct cfs_hash_head *)&bd->bd_bucket->hsb_head[0];
        return &head[bd->bd_offset].hh_head;
}

static int
cfs_hash_hh_hnode_add(struct cfs_hash *hs, struct cfs_hash_bd *bd,
                      struct hlist_node *hnode)
{
        hlist_add_head(hnode, cfs_hash_hh_hhead(hs, bd));
        return -1; /* unknown depth */
}

static int
cfs_hash_hh_hnode_del(struct cfs_hash *hs, struct cfs_hash_bd *bd,
                      struct hlist_node *hnode)
{
        hlist_del_init(hnode);
        return -1; /* unknown depth */
}

/**
 * Simple hash head with depth tracking
 * new element is always added to head of hlist
 */
struct cfs_hash_head_dep {
        struct hlist_head       hd_head;        /**< entries list */
        unsigned int            hd_depth;       /**< list length */
};

static int
cfs_hash_hd_hhead_size(struct cfs_hash *hs)
{
        return sizeof(struct cfs_hash_head_dep);
}

static struct hlist_head *
cfs_hash_hd_hhead(struct cfs_hash *hs, struct cfs_hash_bd *bd)
{
        struct cfs_hash_head_dep *head;

        head = (struct cfs_hash_head_dep *)&bd->bd_bucket->hsb_head[0];
        return &head[bd->bd_offset].hd_head;
}

static int
cfs_hash_hd_hnode_add(struct cfs_hash *hs, struct cfs_hash_bd *bd,
                      struct hlist_node *hnode)
{
        struct cfs_hash_head_dep *hh;

        hh = container_of(cfs_hash_hd_hhead(hs, bd),
                          struct cfs_hash_head_dep, hd_head);
        hlist_add_head(hnode, &hh->hd_head);
        return ++hh->hd_depth;
}

static int
cfs_hash_hd_hnode_del(struct cfs_hash *hs, struct cfs_hash_bd *bd,
                      struct hlist_node *hnode)
{
        struct cfs_hash_head_dep *hh;

        hh = container_of(cfs_hash_hd_hhead(hs, bd),
                          struct cfs_hash_head_dep, hd_head);
        hlist_del_init(hnode);
        return --hh->hd_depth;
}

/**
 * double links hash head without depth tracking
 * new element is always added to tail of hlist
 */
struct cfs_hash_dhead {
        struct hlist_head       dh_head;        /**< entries list */
        struct hlist_node       *dh_tail;       /**< the last entry */
};

static int
cfs_hash_dh_hhead_size(struct cfs_hash *hs)
{
        return sizeof(struct cfs_hash_dhead);
}

static struct hlist_head *
cfs_hash_dh_hhead(struct cfs_hash *hs, struct cfs_hash_bd *bd)
{
        struct cfs_hash_dhead *head;

        head = (struct cfs_hash_dhead *)&bd->bd_bucket->hsb_head[0];
        return &head[bd->bd_offset].dh_head;
}

static int
cfs_hash_dh_hnode_add(struct cfs_hash *hs, struct cfs_hash_bd *bd,
                      struct hlist_node *hnode)
{
        struct cfs_hash_dhead *dh;

        dh = container_of(cfs_hash_dh_hhead(hs, bd),
                          struct cfs_hash_dhead, dh_head);
        if (dh->dh_tail) /* not empty */
                hlist_add_behind(hnode, dh->dh_tail);
        else /* empty list */
                hlist_add_head(hnode, &dh->dh_head);
        dh->dh_tail = hnode;
        return -1; /* unknown depth */
}

static int
cfs_hash_dh_hnode_del(struct cfs_hash *hs, struct cfs_hash_bd *bd,
                      struct hlist_node *hnd)
{
        struct cfs_hash_dhead *dh;

        dh = container_of(cfs_hash_dh_hhead(hs, bd),
                          struct cfs_hash_dhead, dh_head);
        if (!hnd->next) { /* it's the tail */
                dh->dh_tail = (hnd->pprev == &dh->dh_head.first) ? NULL :
                              container_of(hnd->pprev, struct hlist_node, next);
        }
        hlist_del_init(hnd);
        return -1; /* unknown depth */
}

/**
 * double links hash head with depth tracking
 * new element is always added to tail of hlist
 */
struct cfs_hash_dhead_dep {
        struct hlist_head       dd_head;        /**< entries list */
        struct hlist_node       *dd_tail;       /**< the last entry */
        unsigned int            dd_depth;       /**< list length */
};

static int
cfs_hash_dd_hhead_size(struct cfs_hash *hs)
{
        return sizeof(struct cfs_hash_dhead_dep);
}

static struct hlist_head *
cfs_hash_dd_hhead(struct cfs_hash *hs, struct cfs_hash_bd *bd)
{
        struct cfs_hash_dhead_dep *head;

        head = (struct cfs_hash_dhead_dep *)&bd->bd_bucket->hsb_head[0];
        return &head[bd->bd_offset].dd_head;
}

static int
cfs_hash_dd_hnode_add(struct cfs_hash *hs, struct cfs_hash_bd *bd,
                      struct hlist_node *hnode)
{
        struct cfs_hash_dhead_dep *dh;

        dh = container_of(cfs_hash_dd_hhead(hs, bd),
                          struct cfs_hash_dhead_dep, dd_head);
        if (dh->dd_tail) /* not empty */
                hlist_add_behind(hnode, dh->dd_tail);
        else /* empty list */
                hlist_add_head(hnode, &dh->dd_head);
        dh->dd_tail = hnode;
        return ++dh->dd_depth;
}

static int
cfs_hash_dd_hnode_del(struct cfs_hash *hs, struct cfs_hash_bd *bd,
                      struct hlist_node *hnd)
{
        struct cfs_hash_dhead_dep *dh;

        dh = container_of(cfs_hash_dd_hhead(hs, bd),
                          struct cfs_hash_dhead_dep, dd_head);
        if (!hnd->next) { /* it's the tail */
                dh->dd_tail = (hnd->pprev == &dh->dd_head.first) ? NULL :
                              container_of(hnd->pprev, struct hlist_node, next);
        }
        hlist_del_init(hnd);
        return --dh->dd_depth;
}

static struct cfs_hash_hlist_ops cfs_hash_hh_hops = {
        .hop_hhead      = cfs_hash_hh_hhead,
        .hop_hhead_size = cfs_hash_hh_hhead_size,
        .hop_hnode_add  = cfs_hash_hh_hnode_add,
        .hop_hnode_del  = cfs_hash_hh_hnode_del,
};

static struct cfs_hash_hlist_ops cfs_hash_hd_hops = {
        .hop_hhead      = cfs_hash_hd_hhead,
        .hop_hhead_size = cfs_hash_hd_hhead_size,
        .hop_hnode_add  = cfs_hash_hd_hnode_add,
        .hop_hnode_del  = cfs_hash_hd_hnode_del,
};

static struct cfs_hash_hlist_ops cfs_hash_dh_hops = {
        .hop_hhead      = cfs_hash_dh_hhead,
        .hop_hhead_size = cfs_hash_dh_hhead_size,
        .hop_hnode_add  = cfs_hash_dh_hnode_add,
        .hop_hnode_del  = cfs_hash_dh_hnode_del,
};

static struct cfs_hash_hlist_ops cfs_hash_dd_hops = {
        .hop_hhead      = cfs_hash_dd_hhead,
        .hop_hhead_size = cfs_hash_dd_hhead_size,
        .hop_hnode_add  = cfs_hash_dd_hnode_add,
        .hop_hnode_del  = cfs_hash_dd_hnode_del,
};

static void
cfs_hash_hlist_setup(struct cfs_hash *hs)
{
        if (cfs_hash_with_add_tail(hs)) {
                hs->hs_hops = cfs_hash_with_depth(hs) ?
                              &cfs_hash_dd_hops : &cfs_hash_dh_hops;
        } else {
                hs->hs_hops = cfs_hash_with_depth(hs) ?
                              &cfs_hash_hd_hops : &cfs_hash_hh_hops;
        }
}

static void
cfs_hash_bd_from_key(struct cfs_hash *hs, struct cfs_hash_bucket **bkts,
                     unsigned int bits, const void *key, struct cfs_hash_bd *bd)
{
        unsigned int index = cfs_hash_id(hs, key, (1U << bits) - 1);

        LASSERT(bits == hs->hs_cur_bits || bits == hs->hs_rehash_bits);

        bd->bd_bucket = bkts[index & ((1U << (bits - hs->hs_bkt_bits)) - 1)];
        bd->bd_offset = index >> (bits - hs->hs_bkt_bits);
}

void
cfs_hash_bd_get(struct cfs_hash *hs, const void *key, struct cfs_hash_bd *bd)
{
        /* NB: caller should hold hs->hs_rwlock if REHASH is set */
        if (likely(!hs->hs_rehash_buckets)) {
                cfs_hash_bd_from_key(hs, hs->hs_buckets,
                                     hs->hs_cur_bits, key, bd);
        } else {
                LASSERT(hs->hs_rehash_bits);
                cfs_hash_bd_from_key(hs, hs->hs_rehash_buckets,
                                     hs->hs_rehash_bits, key, bd);
        }
}
EXPORT_SYMBOL(cfs_hash_bd_get);

static inline void
cfs_hash_bd_dep_record(struct cfs_hash *hs, struct cfs_hash_bd *bd, int dep_cur)
{
        if (likely(dep_cur <= bd->bd_bucket->hsb_depmax))
                return;

        bd->bd_bucket->hsb_depmax = dep_cur;
# if CFS_HASH_DEBUG_LEVEL >= CFS_HASH_DEBUG_1
        if (likely(!warn_on_depth ||
                   max(warn_on_depth, hs->hs_dep_max) >= dep_cur))
                return;

        spin_lock(&hs->hs_dep_lock);
        hs->hs_dep_max = dep_cur;
        hs->hs_dep_bkt = bd->bd_bucket->hsb_index;
        hs->hs_dep_off = bd->bd_offset;
        hs->hs_dep_bits = hs->hs_cur_bits;
        spin_unlock(&hs->hs_dep_lock);

        cfs_wi_schedule(cfs_sched_rehash, &hs->hs_dep_wi);
# endif
}

void
cfs_hash_bd_add_locked(struct cfs_hash *hs, struct cfs_hash_bd *bd,
                       struct hlist_node *hnode)
{
        int rc;

        rc = hs->hs_hops->hop_hnode_add(hs, bd, hnode);
        cfs_hash_bd_dep_record(hs, bd, rc);
        bd->bd_bucket->hsb_version++;
        if (unlikely(!bd->bd_bucket->hsb_version))
                bd->bd_bucket->hsb_version++;
        bd->bd_bucket->hsb_count++;

        if (cfs_hash_with_counter(hs))
                atomic_inc(&hs->hs_count);
        if (!cfs_hash_with_no_itemref(hs))
                cfs_hash_get(hs, hnode);
}
EXPORT_SYMBOL(cfs_hash_bd_add_locked);

void
cfs_hash_bd_del_locked(struct cfs_hash *hs, struct cfs_hash_bd *bd,
                       struct hlist_node *hnode)
{
        hs->hs_hops->hop_hnode_del(hs, bd, hnode);

        LASSERT(bd->bd_bucket->hsb_count > 0);
        bd->bd_bucket->hsb_count--;
        bd->bd_bucket->hsb_version++;
        if (unlikely(!bd->bd_bucket->hsb_version))
                bd->bd_bucket->hsb_version++;

        if (cfs_hash_with_counter(hs)) {
                LASSERT(atomic_read(&hs->hs_count) > 0);
                atomic_dec(&hs->hs_count);
        }
        if (!cfs_hash_with_no_itemref(hs))
                cfs_hash_put_locked(hs, hnode);
}
EXPORT_SYMBOL(cfs_hash_bd_del_locked);

void
cfs_hash_bd_move_locked(struct cfs_hash *hs, struct cfs_hash_bd *bd_old,
                        struct cfs_hash_bd *bd_new, struct hlist_node *hnode)
{
        struct cfs_hash_bucket *obkt = bd_old->bd_bucket;
        struct cfs_hash_bucket *nbkt = bd_new->bd_bucket;
        int rc;

        if (!cfs_hash_bd_compare(bd_old, bd_new))
                return;

        /* use cfs_hash_bd_hnode_add/del, to avoid atomic & refcount ops
         * in cfs_hash_bd_del/add_locked
         */
        hs->hs_hops->hop_hnode_del(hs, bd_old, hnode);
        rc = hs->hs_hops->hop_hnode_add(hs, bd_new, hnode);
        cfs_hash_bd_dep_record(hs, bd_new, rc);

        LASSERT(obkt->hsb_count > 0);
        obkt->hsb_count--;
        obkt->hsb_version++;
        if (unlikely(!obkt->hsb_version))
                obkt->hsb_version++;
        nbkt->hsb_count++;
        nbkt->hsb_version++;
        if (unlikely(!nbkt->hsb_version))
                nbkt->hsb_version++;
}

enum {
        /** always set, for sanity (avoid ZERO intent) */
        CFS_HS_LOOKUP_MASK_FIND = BIT(0),
        /** return entry with a ref */
        CFS_HS_LOOKUP_MASK_REF  = BIT(1),
        /** add entry if not existing */
        CFS_HS_LOOKUP_MASK_ADD  = BIT(2),
        /** delete entry, ignore other masks */
        CFS_HS_LOOKUP_MASK_DEL  = BIT(3),
};

enum cfs_hash_lookup_intent {
        /** return item w/o refcount */
        CFS_HS_LOOKUP_IT_PEEK    = CFS_HS_LOOKUP_MASK_FIND,
        /** return item with refcount */
        CFS_HS_LOOKUP_IT_FIND    = (CFS_HS_LOOKUP_MASK_FIND |
                                    CFS_HS_LOOKUP_MASK_REF),
        /** return item w/o refcount if existed, otherwise add */
        CFS_HS_LOOKUP_IT_ADD     = (CFS_HS_LOOKUP_MASK_FIND |
                                    CFS_HS_LOOKUP_MASK_ADD),
        /** return item with refcount if existed, otherwise add */
        CFS_HS_LOOKUP_IT_FINDADD = (CFS_HS_LOOKUP_IT_FIND |
                                    CFS_HS_LOOKUP_MASK_ADD),
        /** delete if existed */
        CFS_HS_LOOKUP_IT_FINDDEL = (CFS_HS_LOOKUP_MASK_FIND |
                                    CFS_HS_LOOKUP_MASK_DEL)
};

static struct hlist_node *
cfs_hash_bd_lookup_intent(struct cfs_hash *hs, struct cfs_hash_bd *bd,
                          const void *key, struct hlist_node *hnode,
                          enum cfs_hash_lookup_intent intent)

{
        struct hlist_head *hhead = cfs_hash_bd_hhead(hs, bd);
        struct hlist_node *ehnode;
        struct hlist_node *match;
        int intent_add = intent & CFS_HS_LOOKUP_MASK_ADD;

        /* with this function, we can avoid a lot of useless refcount ops,
         * which are expensive atomic operations most time.
         */
        match = intent_add ? NULL : hnode;
        hlist_for_each(ehnode, hhead) {
                if (!cfs_hash_keycmp(hs, key, ehnode))
                        continue;

                if (match && match != ehnode) /* can't match */
                        continue;

                /* match and ... */
                if (intent & CFS_HS_LOOKUP_MASK_DEL) {
                        cfs_hash_bd_del_locked(hs, bd, ehnode);
                        return ehnode;
                }

                /* caller wants refcount? */
                if (intent & CFS_HS_LOOKUP_MASK_REF)
                        cfs_hash_get(hs, ehnode);
                return ehnode;
        }
        /* no match item */
        if (!intent_add)
                return NULL;

        LASSERT(hnode);
        cfs_hash_bd_add_locked(hs, bd, hnode);
        return hnode;
}

struct hlist_node *
cfs_hash_bd_lookup_locked(struct cfs_hash *hs, struct cfs_hash_bd *bd,
                          const void *key)
{
        return cfs_hash_bd_lookup_intent(hs, bd, key, NULL,
                                         CFS_HS_LOOKUP_IT_FIND);
}
EXPORT_SYMBOL(cfs_hash_bd_lookup_locked);

struct hlist_node *
cfs_hash_bd_peek_locked(struct cfs_hash *hs, struct cfs_hash_bd *bd,
                        const void *key)
{
        return cfs_hash_bd_lookup_intent(hs, bd, key, NULL,
                                         CFS_HS_LOOKUP_IT_PEEK);
}
EXPORT_SYMBOL(cfs_hash_bd_peek_locked);

static void
cfs_hash_multi_bd_lock(struct cfs_hash *hs, struct cfs_hash_bd *bds,
                       unsigned int n, int excl)
{
        struct cfs_hash_bucket *prev = NULL;
        int i;

        /**
         * bds must be ascendantly ordered by bd->bd_bucket->hsb_index.
         * NB: it's possible that several bds point to the same bucket but
         * have different bd::bd_offset, so need take care of deadlock.
         */
        cfs_hash_for_each_bd(bds, n, i) {
                if (prev == bds[i].bd_bucket)
                        continue;

                LASSERT(!prev || prev->hsb_index < bds[i].bd_bucket->hsb_index);
                cfs_hash_bd_lock(hs, &bds[i], excl);
                prev = bds[i].bd_bucket;
        }
}

static void
cfs_hash_multi_bd_unlock(struct cfs_hash *hs, struct cfs_hash_bd *bds,
                         unsigned int n, int excl)
{
        struct cfs_hash_bucket *prev = NULL;
        int i;

        cfs_hash_for_each_bd(bds, n, i) {
                if (prev != bds[i].bd_bucket) {
                        cfs_hash_bd_unlock(hs, &bds[i], excl);
                        prev = bds[i].bd_bucket;
                }
        }
}

static struct hlist_node *
cfs_hash_multi_bd_lookup_locked(struct cfs_hash *hs, struct cfs_hash_bd *bds,
                                unsigned int n, const void *key)
{
        struct hlist_node *ehnode;
        unsigned int i;

        cfs_hash_for_each_bd(bds, n, i) {
                ehnode = cfs_hash_bd_lookup_intent(hs, &bds[i], key, NULL,
                                                   CFS_HS_LOOKUP_IT_FIND);
                if (ehnode)
                        return ehnode;
        }
        return NULL;
}

static struct hlist_node *
cfs_hash_multi_bd_findadd_locked(struct cfs_hash *hs, struct cfs_hash_bd *bds,
                                 unsigned int n, const void *key,
                                 struct hlist_node *hnode, int noref)
{
        struct hlist_node *ehnode;
        int intent;
        unsigned int i;

        LASSERT(hnode);
        intent = (!noref * CFS_HS_LOOKUP_MASK_REF) | CFS_HS_LOOKUP_IT_PEEK;

        cfs_hash_for_each_bd(bds, n, i) {
                ehnode = cfs_hash_bd_lookup_intent(hs, &bds[i], key,
                                                   NULL, intent);
                if (ehnode)
                        return ehnode;
        }

        if (i == 1) { /* only one bucket */
                cfs_hash_bd_add_locked(hs, &bds[0], hnode);
        } else {
                struct cfs_hash_bd mybd;

                cfs_hash_bd_get(hs, key, &mybd);
                cfs_hash_bd_add_locked(hs, &mybd, hnode);
        }

        return hnode;
}

static struct hlist_node *
cfs_hash_multi_bd_finddel_locked(struct cfs_hash *hs, struct cfs_hash_bd *bds,
                                 unsigned int n, const void *key,
                                 struct hlist_node *hnode)
{
        struct hlist_node *ehnode;
        unsigned int i;

        cfs_hash_for_each_bd(bds, n, i) {
                ehnode = cfs_hash_bd_lookup_intent(hs, &bds[i], key, hnode,
                                                   CFS_HS_LOOKUP_IT_FINDDEL);
                if (ehnode)
                        return ehnode;
        }
        return NULL;
}

static void
cfs_hash_bd_order(struct cfs_hash_bd *bd1, struct cfs_hash_bd *bd2)
{
        int rc;

        if (!bd2->bd_bucket)
                return;

        if (!bd1->bd_bucket) {
                *bd1 = *bd2;
                bd2->bd_bucket = NULL;
                return;
        }

        rc = cfs_hash_bd_compare(bd1, bd2);
        if (!rc)
                bd2->bd_bucket = NULL;
        else if (rc > 0)
                swap(*bd1, *bd2); /* swap bd1 and bd2 */
}

void
cfs_hash_dual_bd_get(struct cfs_hash *hs, const void *key,
                     struct cfs_hash_bd *bds)
{
        /* NB: caller should hold hs_lock.rw if REHASH is set */
        cfs_hash_bd_from_key(hs, hs->hs_buckets,
                             hs->hs_cur_bits, key, &bds[0]);
        if (likely(!hs->hs_rehash_buckets)) {
                /* no rehash or not rehashing */
                bds[1].bd_bucket = NULL;
                return;
        }

        LASSERT(hs->hs_rehash_bits);
        cfs_hash_bd_from_key(hs, hs->hs_rehash_buckets,
                             hs->hs_rehash_bits, key, &bds[1]);

        cfs_hash_bd_order(&bds[0], &bds[1]);
}

void
cfs_hash_dual_bd_lock(struct cfs_hash *hs, struct cfs_hash_bd *bds, int excl)
{
        cfs_hash_multi_bd_lock(hs, bds, 2, excl);
}

void
cfs_hash_dual_bd_unlock(struct cfs_hash *hs, struct cfs_hash_bd *bds, int excl)
{
        cfs_hash_multi_bd_unlock(hs, bds, 2, excl);
}

struct hlist_node *
cfs_hash_dual_bd_lookup_locked(struct cfs_hash *hs, struct cfs_hash_bd *bds,
                               const void *key)
{
        return cfs_hash_multi_bd_lookup_locked(hs, bds, 2, key);
}

struct hlist_node *
cfs_hash_dual_bd_findadd_locked(struct cfs_hash *hs, struct cfs_hash_bd *bds,
                                const void *key, struct hlist_node *hnode,
                                int noref)
{
        return cfs_hash_multi_bd_findadd_locked(hs, bds, 2, key,
                                                hnode, noref);
}

struct hlist_node *
cfs_hash_dual_bd_finddel_locked(struct cfs_hash *hs, struct cfs_hash_bd *bds,
                                const void *key, struct hlist_node *hnode)
{
        return cfs_hash_multi_bd_finddel_locked(hs, bds, 2, key, hnode);
}

static void
cfs_hash_buckets_free(struct cfs_hash_bucket **buckets,
                      int bkt_size, int prev_size, int size)
{
        int i;

        for (i = prev_size; i < size; i++) {
                if (buckets[i])
                        LIBCFS_FREE(buckets[i], bkt_size);
        }

        LIBCFS_FREE(buckets, sizeof(buckets[0]) * size);
}

/*
 * Create or grow bucket memory. Return old_buckets if no allocation was
 * needed, the newly allocated buckets if allocation was needed and
 * successful, and NULL on error.
 */
static struct cfs_hash_bucket **
cfs_hash_buckets_realloc(struct cfs_hash *hs, struct cfs_hash_bucket **old_bkts,
                         unsigned int old_size, unsigned int new_size)
{
        struct cfs_hash_bucket **new_bkts;
        int i;

        LASSERT(!old_size || old_bkts);

        if (old_bkts && old_size == new_size)
                return old_bkts;

        LIBCFS_ALLOC(new_bkts, sizeof(new_bkts[0]) * new_size);
        if (!new_bkts)
                return NULL;

        if (old_bkts) {
                memcpy(new_bkts, old_bkts,
                       min(old_size, new_size) * sizeof(*old_bkts));
        }

        for (i = old_size; i < new_size; i++) {
                struct hlist_head *hhead;
                struct cfs_hash_bd bd;

                LIBCFS_ALLOC(new_bkts[i], cfs_hash_bkt_size(hs));
                if (!new_bkts[i]) {
                        cfs_hash_buckets_free(new_bkts, cfs_hash_bkt_size(hs),
                                              old_size, new_size);
                        return NULL;
                }

                new_bkts[i]->hsb_index = i;
                new_bkts[i]->hsb_version = 1;   /* shouldn't be zero */
                new_bkts[i]->hsb_depmax = -1;   /* unknown */
                bd.bd_bucket = new_bkts[i];
                cfs_hash_bd_for_each_hlist(hs, &bd, hhead)
                        INIT_HLIST_HEAD(hhead);

                if (cfs_hash_with_no_lock(hs) ||
                    cfs_hash_with_no_bktlock(hs))
                        continue;

                if (cfs_hash_with_rw_bktlock(hs))
                        rwlock_init(&new_bkts[i]->hsb_lock.rw);
                else if (cfs_hash_with_spin_bktlock(hs))
                        spin_lock_init(&new_bkts[i]->hsb_lock.spin);
                else
                        LBUG(); /* invalid use-case */
        }
        return new_bkts;
}

/**
 * Initialize new libcfs hash, where:
 * @name     - Descriptive hash name
 * @cur_bits - Initial hash table size, in bits
 * @max_bits - Maximum allowed hash table resize, in bits
 * @ops      - Registered hash table operations
 * @flags    - CFS_HASH_REHASH enable synamic hash resizing
 *           - CFS_HASH_SORT enable chained hash sort
 */
static int cfs_hash_rehash_worker(struct cfs_workitem *wi);

#if CFS_HASH_DEBUG_LEVEL >= CFS_HASH_DEBUG_1
static int cfs_hash_dep_print(struct cfs_workitem *wi)
{
        struct cfs_hash *hs = container_of(wi, struct cfs_hash, hs_dep_wi);
        int dep;
        int bkt;
        int off;
        int bits;

        spin_lock(&hs->hs_dep_lock);
        dep = hs->hs_dep_max;
        bkt = hs->hs_dep_bkt;
        off = hs->hs_dep_off;
        bits = hs->hs_dep_bits;
        spin_unlock(&hs->hs_dep_lock);

        LCONSOLE_WARN("#### HASH %s (bits: %d): max depth %d at bucket %d/%d\n",
                      hs->hs_name, bits, dep, bkt, off);
        spin_lock(&hs->hs_dep_lock);
        hs->hs_dep_bits = 0; /* mark as workitem done */
        spin_unlock(&hs->hs_dep_lock);
        return 0;
}

static void cfs_hash_depth_wi_init(struct cfs_hash *hs)
{
        spin_lock_init(&hs->hs_dep_lock);
        cfs_wi_init(&hs->hs_dep_wi, hs, cfs_hash_dep_print);
}

static void cfs_hash_depth_wi_cancel(struct cfs_hash *hs)
{
        if (cfs_wi_deschedule(cfs_sched_rehash, &hs->hs_dep_wi))
                return;

        spin_lock(&hs->hs_dep_lock);
        while (hs->hs_dep_bits) {
                spin_unlock(&hs->hs_dep_lock);
                cond_resched();
                spin_lock(&hs->hs_dep_lock);
        }
        spin_unlock(&hs->hs_dep_lock);
}

#else /* CFS_HASH_DEBUG_LEVEL < CFS_HASH_DEBUG_1 */

static inline void cfs_hash_depth_wi_init(struct cfs_hash *hs) {}
static inline void cfs_hash_depth_wi_cancel(struct cfs_hash *hs) {}

#endif /* CFS_HASH_DEBUG_LEVEL >= CFS_HASH_DEBUG_1 */

struct cfs_hash *
cfs_hash_create(char *name, unsigned int cur_bits, unsigned int max_bits,
                unsigned int bkt_bits, unsigned int extra_bytes,
                unsigned int min_theta, unsigned int max_theta,
                struct cfs_hash_ops *ops, unsigned int flags)
{
        struct cfs_hash *hs;
        int len;

        BUILD_BUG_ON(CFS_HASH_THETA_BITS >= 15);

        LASSERT(name);
        LASSERT(ops->hs_key);
        LASSERT(ops->hs_hash);
        LASSERT(ops->hs_object);
        LASSERT(ops->hs_keycmp);
        LASSERT(ops->hs_get);
        LASSERT(ops->hs_put || ops->hs_put_locked);

        if (flags & CFS_HASH_REHASH)
                flags |= CFS_HASH_COUNTER; /* must have counter */

        LASSERT(cur_bits > 0);
        LASSERT(cur_bits >= bkt_bits);
        LASSERT(max_bits >= cur_bits && max_bits < 31);
        LASSERT(ergo(!(flags & CFS_HASH_REHASH), cur_bits == max_bits));
        LASSERT(ergo(flags & CFS_HASH_REHASH, !(flags & CFS_HASH_NO_LOCK)));
        LASSERT(ergo(flags & CFS_HASH_REHASH_KEY, ops->hs_keycpy));

        len = !(flags & CFS_HASH_BIGNAME) ?
              CFS_HASH_NAME_LEN : CFS_HASH_BIGNAME_LEN;
        LIBCFS_ALLOC(hs, offsetof(struct cfs_hash, hs_name[len]));
        if (!hs)
                return NULL;

        strlcpy(hs->hs_name, name, len);
        hs->hs_flags = flags;

        atomic_set(&hs->hs_refcount, 1);
        atomic_set(&hs->hs_count, 0);

        cfs_hash_lock_setup(hs);
        cfs_hash_hlist_setup(hs);

        hs->hs_cur_bits = (u8)cur_bits;
        hs->hs_min_bits = (u8)cur_bits;
        hs->hs_max_bits = (u8)max_bits;
        hs->hs_bkt_bits = (u8)bkt_bits;

        hs->hs_ops = ops;
        hs->hs_extra_bytes = extra_bytes;
        hs->hs_rehash_bits = 0;
        cfs_wi_init(&hs->hs_rehash_wi, hs, cfs_hash_rehash_worker);
        cfs_hash_depth_wi_init(hs);

        if (cfs_hash_with_rehash(hs))
                __cfs_hash_set_theta(hs, min_theta, max_theta);

        hs->hs_buckets = cfs_hash_buckets_realloc(hs, NULL, 0,
                                                  CFS_HASH_NBKT(hs));
        if (hs->hs_buckets)
                return hs;

        LIBCFS_FREE(hs, offsetof(struct cfs_hash, hs_name[len]));
        return NULL;
}
EXPORT_SYMBOL(cfs_hash_create);

/**
 * Cleanup libcfs hash @hs.
 */
static void
cfs_hash_destroy(struct cfs_hash *hs)
{
        struct hlist_node *hnode;
        struct hlist_node *pos;
        struct cfs_hash_bd bd;
        int i;

        LASSERT(hs);
        LASSERT(!cfs_hash_is_exiting(hs) &&
                !cfs_hash_is_iterating(hs));

        /**
         * prohibit further rehashes, don't need any lock because
         * I'm the only (last) one can change it.
         */
        hs->hs_exiting = 1;
        if (cfs_hash_with_rehash(hs))
                cfs_hash_rehash_cancel(hs);

        cfs_hash_depth_wi_cancel(hs);
        /* rehash should be done/canceled */
        LASSERT(hs->hs_buckets && !hs->hs_rehash_buckets);

        cfs_hash_for_each_bucket(hs, &bd, i) {
                struct hlist_head *hhead;

                LASSERT(bd.bd_bucket);
                /* no need to take this lock, just for consistent code */
                cfs_hash_bd_lock(hs, &bd, 1);

                cfs_hash_bd_for_each_hlist(hs, &bd, hhead) {
                        hlist_for_each_safe(hnode, pos, hhead) {
                                LASSERTF(!cfs_hash_with_assert_empty(hs),
                                         "hash %s bucket %u(%u) is not empty: %u items left\n",
                                         hs->hs_name, bd.bd_bucket->hsb_index,
                                         bd.bd_offset, bd.bd_bucket->hsb_count);
                                /* can't assert key valicate, because we
                                 * can interrupt rehash
                                 */
                                cfs_hash_bd_del_locked(hs, &bd, hnode);
                                cfs_hash_exit(hs, hnode);
                        }
                }
                LASSERT(!bd.bd_bucket->hsb_count);
                cfs_hash_bd_unlock(hs, &bd, 1);
                cond_resched();
        }

        LASSERT(!atomic_read(&hs->hs_count));

        cfs_hash_buckets_free(hs->hs_buckets, cfs_hash_bkt_size(hs),
                              0, CFS_HASH_NBKT(hs));
        i = cfs_hash_with_bigname(hs) ?
            CFS_HASH_BIGNAME_LEN : CFS_HASH_NAME_LEN;
        LIBCFS_FREE(hs, offsetof(struct cfs_hash, hs_name[i]));
}

struct cfs_hash *cfs_hash_getref(struct cfs_hash *hs)
{
        if (atomic_inc_not_zero(&hs->hs_refcount))
                return hs;
        return NULL;
}
EXPORT_SYMBOL(cfs_hash_getref);

void cfs_hash_putref(struct cfs_hash *hs)
{
        if (atomic_dec_and_test(&hs->hs_refcount))
                cfs_hash_destroy(hs);
}
EXPORT_SYMBOL(cfs_hash_putref);

static inline int
cfs_hash_rehash_bits(struct cfs_hash *hs)
{
        if (cfs_hash_with_no_lock(hs) ||
            !cfs_hash_with_rehash(hs))
                return -EOPNOTSUPP;

        if (unlikely(cfs_hash_is_exiting(hs)))
                return -ESRCH;

        if (unlikely(cfs_hash_is_rehashing(hs)))
                return -EALREADY;

        if (unlikely(cfs_hash_is_iterating(hs)))
                return -EAGAIN;

        /* XXX: need to handle case with max_theta != 2.0
         *      and the case with min_theta != 0.5
         */
        if ((hs->hs_cur_bits < hs->hs_max_bits) &&
            (__cfs_hash_theta(hs) > hs->hs_max_theta))
                return hs->hs_cur_bits + 1;

        if (!cfs_hash_with_shrink(hs))
                return 0;

        if ((hs->hs_cur_bits > hs->hs_min_bits) &&
            (__cfs_hash_theta(hs) < hs->hs_min_theta))
                return hs->hs_cur_bits - 1;

        return 0;
}

/**
 * don't allow inline rehash if:
 * - user wants non-blocking change (add/del) on hash table
 * - too many elements
 */
static inline int
cfs_hash_rehash_inline(struct cfs_hash *hs)
{
        return !cfs_hash_with_nblk_change(hs) &&
               atomic_read(&hs->hs_count) < CFS_HASH_LOOP_HOG;
}

/**
 * Add item @hnode to libcfs hash @hs using @key.  The registered
 * ops->hs_get function will be called when the item is added.
 */
void
cfs_hash_add(struct cfs_hash *hs, const void *key, struct hlist_node *hnode)
{
        struct cfs_hash_bd bd;
        int bits;

        LASSERT(hlist_unhashed(hnode));

        cfs_hash_lock(hs, 0);
        cfs_hash_bd_get_and_lock(hs, key, &bd, 1);

        cfs_hash_key_validate(hs, key, hnode);
        cfs_hash_bd_add_locked(hs, &bd, hnode);

        cfs_hash_bd_unlock(hs, &bd, 1);

        bits = cfs_hash_rehash_bits(hs);
        cfs_hash_unlock(hs, 0);
        if (bits > 0)
                cfs_hash_rehash(hs, cfs_hash_rehash_inline(hs));
}
EXPORT_SYMBOL(cfs_hash_add);

static struct hlist_node *
cfs_hash_find_or_add(struct cfs_hash *hs, const void *key,
                     struct hlist_node *hnode, int noref)
{
        struct hlist_node *ehnode;
        struct cfs_hash_bd bds[2];
        int bits = 0;

        LASSERTF(hlist_unhashed(hnode), "hnode = %p\n", hnode);

        cfs_hash_lock(hs, 0);
        cfs_hash_dual_bd_get_and_lock(hs, key, bds, 1);

        cfs_hash_key_validate(hs, key, hnode);
        ehnode = cfs_hash_dual_bd_findadd_locked(hs, bds, key,
                                                 hnode, noref);
        cfs_hash_dual_bd_unlock(hs, bds, 1);

        if (ehnode == hnode)    /* new item added */
                bits = cfs_hash_rehash_bits(hs);
        cfs_hash_unlock(hs, 0);
        if (bits > 0)
                cfs_hash_rehash(hs, cfs_hash_rehash_inline(hs));

        return ehnode;
}

/**
 * Add item @hnode to libcfs hash @hs using @key.  The registered
 * ops->hs_get function will be called if the item was added.
 * Returns 0 on success or -EALREADY on key collisions.
 */
int
cfs_hash_add_unique(struct cfs_hash *hs, const void *key,
                    struct hlist_node *hnode)
{
        return cfs_hash_find_or_add(hs, key, hnode, 1) != hnode ?
               -EALREADY : 0;
}
EXPORT_SYMBOL(cfs_hash_add_unique);

/**
 * Add item @hnode to libcfs hash @hs using @key.  If this @key
 * already exists in the hash then ops->hs_get will be called on the
 * conflicting entry and that entry will be returned to the caller.
 * Otherwise ops->hs_get is called on the item which was added.
 */
void *
cfs_hash_findadd_unique(struct cfs_hash *hs, const void *key,
                        struct hlist_node *hnode)
{
        hnode = cfs_hash_find_or_add(hs, key, hnode, 0);

        return cfs_hash_object(hs, hnode);
}
EXPORT_SYMBOL(cfs_hash_findadd_unique);

/**
 * Delete item @hnode from the libcfs hash @hs using @key.  The @key
 * is required to ensure the correct hash bucket is locked since there
 * is no direct linkage from the item to the bucket.  The object
 * removed from the hash will be returned and obs->hs_put is called
 * on the removed object.
 */
void *
cfs_hash_del(struct cfs_hash *hs, const void *key, struct hlist_node *hnode)
{
        void *obj = NULL;
        int bits = 0;
        struct cfs_hash_bd bds[2];

        cfs_hash_lock(hs, 0);
        cfs_hash_dual_bd_get_and_lock(hs, key, bds, 1);

        /* NB: do nothing if @hnode is not in hash table */
        if (!hnode || !hlist_unhashed(hnode)) {
                if (!bds[1].bd_bucket && hnode) {
                        cfs_hash_bd_del_locked(hs, &bds[0], hnode);
                } else {
                        hnode = cfs_hash_dual_bd_finddel_locked(hs, bds,
                                                                key, hnode);
                }
        }

        if (hnode) {
                obj = cfs_hash_object(hs, hnode);
                bits = cfs_hash_rehash_bits(hs);
        }

        cfs_hash_dual_bd_unlock(hs, bds, 1);
        cfs_hash_unlock(hs, 0);
        if (bits > 0)
                cfs_hash_rehash(hs, cfs_hash_rehash_inline(hs));

        return obj;
}
EXPORT_SYMBOL(cfs_hash_del);

/**
 * Delete item given @key in libcfs hash @hs.  The first @key found in
 * the hash will be removed, if the key exists multiple times in the hash
 * @hs this function must be called once per key.  The removed object
 * will be returned and ops->hs_put is called on the removed object.
 */
void *
cfs_hash_del_key(struct cfs_hash *hs, const void *key)
{
        return cfs_hash_del(hs, key, NULL);
}
EXPORT_SYMBOL(cfs_hash_del_key);

/**
 * Lookup an item using @key in the libcfs hash @hs and return it.
 * If the @key is found in the hash hs->hs_get() is called and the
 * matching objects is returned.  It is the callers responsibility
 * to call the counterpart ops->hs_put using the cfs_hash_put() macro
 * when when finished with the object.  If the @key was not found
 * in the hash @hs NULL is returned.
 */
void *
cfs_hash_lookup(struct cfs_hash *hs, const void *key)
{
        void *obj = NULL;
        struct hlist_node *hnode;
        struct cfs_hash_bd bds[2];

        cfs_hash_lock(hs, 0);
        cfs_hash_dual_bd_get_and_lock(hs, key, bds, 0);

        hnode = cfs_hash_dual_bd_lookup_locked(hs, bds, key);
        if (hnode)
                obj = cfs_hash_object(hs, hnode);

        cfs_hash_dual_bd_unlock(hs, bds, 0);
        cfs_hash_unlock(hs, 0);

        return obj;
}
EXPORT_SYMBOL(cfs_hash_lookup);

static void
cfs_hash_for_each_enter(struct cfs_hash *hs)
{
        LASSERT(!cfs_hash_is_exiting(hs));

        if (!cfs_hash_with_rehash(hs))
                return;
        /*
         * NB: it's race on cfs_has_t::hs_iterating, but doesn't matter
         * because it's just an unreliable signal to rehash-thread,
         * rehash-thread will try to finish rehash ASAP when seeing this.
         */
        hs->hs_iterating = 1;

        cfs_hash_lock(hs, 1);
        hs->hs_iterators++;

        /* NB: iteration is mostly called by service thread,
         * we tend to cancel pending rehash-request, instead of
         * blocking service thread, we will relaunch rehash request
         * after iteration
         */
        if (cfs_hash_is_rehashing(hs))
                cfs_hash_rehash_cancel_locked(hs);
        cfs_hash_unlock(hs, 1);
}

static void
cfs_hash_for_each_exit(struct cfs_hash *hs)
{
        int remained;
        int bits;

        if (!cfs_hash_with_rehash(hs))
                return;
        cfs_hash_lock(hs, 1);
        remained = --hs->hs_iterators;
        bits = cfs_hash_rehash_bits(hs);
        cfs_hash_unlock(hs, 1);
        /* NB: it's race on cfs_has_t::hs_iterating, see above */
        if (!remained)
                hs->hs_iterating = 0;
        if (bits > 0) {
                cfs_hash_rehash(hs, atomic_read(&hs->hs_count) <
                                    CFS_HASH_LOOP_HOG);
        }
}

/**
 * For each item in the libcfs hash @hs call the passed callback @func
 * and pass to it as an argument each hash item and the private @data.
 *
 * a) the function may sleep!
 * b) during the callback:
 *    . the bucket lock is held so the callback must never sleep.
 *    . if @removal_safe is true, use can remove current item by
 *      cfs_hash_bd_del_locked
 */
static u64
cfs_hash_for_each_tight(struct cfs_hash *hs, cfs_hash_for_each_cb_t func,
                        void *data, int remove_safe)
{
        struct hlist_node *hnode;
        struct hlist_node *pos;
        struct cfs_hash_bd bd;
        u64 count = 0;
        int excl = !!remove_safe;
        int loop = 0;
        int i;

        cfs_hash_for_each_enter(hs);

        cfs_hash_lock(hs, 0);
        LASSERT(!cfs_hash_is_rehashing(hs));

        cfs_hash_for_each_bucket(hs, &bd, i) {
                struct hlist_head *hhead;

                cfs_hash_bd_lock(hs, &bd, excl);
                if (!func) { /* only glimpse size */
                        count += bd.bd_bucket->hsb_count;
                        cfs_hash_bd_unlock(hs, &bd, excl);
                        continue;
                }

                cfs_hash_bd_for_each_hlist(hs, &bd, hhead) {
                        hlist_for_each_safe(hnode, pos, hhead) {
                                cfs_hash_bucket_validate(hs, &bd, hnode);
                                count++;
                                loop++;
                                if (func(hs, &bd, hnode, data)) {
                                        cfs_hash_bd_unlock(hs, &bd, excl);
                                        goto out;
                                }
                        }
                }
                cfs_hash_bd_unlock(hs, &bd, excl);
                if (loop < CFS_HASH_LOOP_HOG)
                        continue;
                loop = 0;
                cfs_hash_unlock(hs, 0);
                cond_resched();
                cfs_hash_lock(hs, 0);
        }
 out:
        cfs_hash_unlock(hs, 0);

        cfs_hash_for_each_exit(hs);
        return count;
}

struct cfs_hash_cond_arg {
        cfs_hash_cond_opt_cb_t  func;
        void                    *arg;
};

static int
cfs_hash_cond_del_locked(struct cfs_hash *hs, struct cfs_hash_bd *bd,
                         struct hlist_node *hnode, void *data)
{
        struct cfs_hash_cond_arg *cond = data;

        if (cond->func(cfs_hash_object(hs, hnode), cond->arg))
                cfs_hash_bd_del_locked(hs, bd, hnode);
        return 0;
}

/**
 * Delete item from the libcfs hash @hs when @func return true.
 * The write lock being hold during loop for each bucket to avoid
 * any object be reference.
 */
void
cfs_hash_cond_del(struct cfs_hash *hs, cfs_hash_cond_opt_cb_t func, void *data)
{
        struct cfs_hash_cond_arg arg = {
                .func   = func,
                .arg    = data,
        };

        cfs_hash_for_each_tight(hs, cfs_hash_cond_del_locked, &arg, 1);
}
EXPORT_SYMBOL(cfs_hash_cond_del);

void
cfs_hash_for_each(struct cfs_hash *hs, cfs_hash_for_each_cb_t func,
                  void *data)
{
        cfs_hash_for_each_tight(hs, func, data, 0);
}
EXPORT_SYMBOL(cfs_hash_for_each);

void
cfs_hash_for_each_safe(struct cfs_hash *hs, cfs_hash_for_each_cb_t func,
                       void *data)
{
        cfs_hash_for_each_tight(hs, func, data, 1);
}
EXPORT_SYMBOL(cfs_hash_for_each_safe);

static int
cfs_hash_peek(struct cfs_hash *hs, struct cfs_hash_bd *bd,
              struct hlist_node *hnode, void *data)
{
        *(int *)data = 0;
        return 1; /* return 1 to break the loop */
}

int
cfs_hash_is_empty(struct cfs_hash *hs)
{
        int empty = 1;

        cfs_hash_for_each_tight(hs, cfs_hash_peek, &empty, 0);
        return empty;
}
EXPORT_SYMBOL(cfs_hash_is_empty);

u64
cfs_hash_size_get(struct cfs_hash *hs)
{
        return cfs_hash_with_counter(hs) ?
               atomic_read(&hs->hs_count) :
               cfs_hash_for_each_tight(hs, NULL, NULL, 0);
}
EXPORT_SYMBOL(cfs_hash_size_get);

/*
 * cfs_hash_for_each_relax:
 * Iterate the hash table and call @func on each item without
 * any lock. This function can't guarantee to finish iteration
 * if these features are enabled:
 *
 *  a. if rehash_key is enabled, an item can be moved from
 *     one bucket to another bucket
 *  b. user can remove non-zero-ref item from hash-table,
 *     so the item can be removed from hash-table, even worse,
 *     it's possible that user changed key and insert to another
 *     hash bucket.
 * there's no way for us to finish iteration correctly on previous
 * two cases, so iteration has to be stopped on change.
 */
static int
cfs_hash_for_each_relax(struct cfs_hash *hs, cfs_hash_for_each_cb_t func,
                        void *data, int start)
{
        struct hlist_node *next = NULL;
        struct hlist_node *hnode;
        struct cfs_hash_bd bd;
        u32 version;
        int count = 0;
        int stop_on_change;
        int has_put_locked;
        int end = -1;
        int rc = 0;
        int i;

        stop_on_change = cfs_hash_with_rehash_key(hs) ||
                         !cfs_hash_with_no_itemref(hs);
        has_put_locked = hs->hs_ops->hs_put_locked != NULL;
        cfs_hash_lock(hs, 0);
again:
        LASSERT(!cfs_hash_is_rehashing(hs));

        cfs_hash_for_each_bucket(hs, &bd, i) {
                struct hlist_head *hhead;

                if (i < start)
                        continue;
                else if (end > 0 && i >= end)
                        break;

                cfs_hash_bd_lock(hs, &bd, 0);
                version = cfs_hash_bd_version_get(&bd);

                cfs_hash_bd_for_each_hlist(hs, &bd, hhead) {
                        hnode = hhead->first;
                        if (!hnode)
                                continue;
                        cfs_hash_get(hs, hnode);

                        for (; hnode; hnode = next) {
                                cfs_hash_bucket_validate(hs, &bd, hnode);
                                next = hnode->next;
                                if (next)
                                        cfs_hash_get(hs, next);
                                cfs_hash_bd_unlock(hs, &bd, 0);
                                cfs_hash_unlock(hs, 0);

                                rc = func(hs, &bd, hnode, data);
                                if (stop_on_change || !has_put_locked)
                                        cfs_hash_put(hs, hnode);
                                cond_resched();
                                count++;

                                cfs_hash_lock(hs, 0);
                                cfs_hash_bd_lock(hs, &bd, 0);
                                if (stop_on_change) {
                                        if (version !=
                                            cfs_hash_bd_version_get(&bd))
                                                rc = -EINTR;
                                } else if (has_put_locked) {
                                        cfs_hash_put_locked(hs, hnode);
                                }
                                if (rc) /* callback wants to break iteration */
                                        break;
                        }
                        if (next) {
                                if (has_put_locked) {
                                        cfs_hash_put_locked(hs, next);
                                        next = NULL;
                                }
                                break;
                        } else if (rc) {
                                break;
                        }
                }
                cfs_hash_bd_unlock(hs, &bd, 0);
                if (next && !has_put_locked) {
                        cfs_hash_put(hs, next);
                        next = NULL;
                }
                if (rc) /* callback wants to break iteration */
                        break;
        }
        if (start > 0 && !rc) {
                end = start;
                start = 0;
                goto again;
        }

        cfs_hash_unlock(hs, 0);
        return count;
}

int
cfs_hash_for_each_nolock(struct cfs_hash *hs, cfs_hash_for_each_cb_t func,
                         void *data, int start)
{
        if (cfs_hash_with_no_lock(hs) ||
            cfs_hash_with_rehash_key(hs) ||
            !cfs_hash_with_no_itemref(hs))
                return -EOPNOTSUPP;

        if (!hs->hs_ops->hs_get ||
            (!hs->hs_ops->hs_put && !hs->hs_ops->hs_put_locked))
                return -EOPNOTSUPP;

        cfs_hash_for_each_enter(hs);
        cfs_hash_for_each_relax(hs, func, data, start);
        cfs_hash_for_each_exit(hs);

        return 0;
}
EXPORT_SYMBOL(cfs_hash_for_each_nolock);

/**
 * For each hash bucket in the libcfs hash @hs call the passed callback
 * @func until all the hash buckets are empty.  The passed callback @func
 * or the previously registered callback hs->hs_put must remove the item
 * from the hash.  You may either use the cfs_hash_del() or hlist_del()
 * functions.  No rwlocks will be held during the callback @func it is
 * safe to sleep if needed.  This function will not terminate until the
 * hash is empty.  Note it is still possible to concurrently add new
 * items in to the hash.  It is the callers responsibility to ensure
 * the required locking is in place to prevent concurrent insertions.
 */
int
cfs_hash_for_each_empty(struct cfs_hash *hs, cfs_hash_for_each_cb_t func,
                        void *data)
{
        unsigned int i = 0;

        if (cfs_hash_with_no_lock(hs))
                return -EOPNOTSUPP;

        if (!hs->hs_ops->hs_get ||
            (!hs->hs_ops->hs_put && !hs->hs_ops->hs_put_locked))
                return -EOPNOTSUPP;

        cfs_hash_for_each_enter(hs);
        while (cfs_hash_for_each_relax(hs, func, data, 0)) {
                CDEBUG(D_INFO, "Try to empty hash: %s, loop: %u\n",
                       hs->hs_name, i++);
        }
        cfs_hash_for_each_exit(hs);
        return 0;
}
EXPORT_SYMBOL(cfs_hash_for_each_empty);

void
cfs_hash_hlist_for_each(struct cfs_hash *hs, unsigned int hindex,
                        cfs_hash_for_each_cb_t func, void *data)
{
        struct hlist_head *hhead;
        struct hlist_node *hnode;
        struct cfs_hash_bd bd;

        cfs_hash_for_each_enter(hs);
        cfs_hash_lock(hs, 0);
        if (hindex >= CFS_HASH_NHLIST(hs))
                goto out;

        cfs_hash_bd_index_set(hs, hindex, &bd);

        cfs_hash_bd_lock(hs, &bd, 0);
        hhead = cfs_hash_bd_hhead(hs, &bd);
        hlist_for_each(hnode, hhead) {
                if (func(hs, &bd, hnode, data))
                        break;
        }
        cfs_hash_bd_unlock(hs, &bd, 0);
out:
        cfs_hash_unlock(hs, 0);
        cfs_hash_for_each_exit(hs);
}
EXPORT_SYMBOL(cfs_hash_hlist_for_each);

/*
 * For each item in the libcfs hash @hs which matches the @key call
 * the passed callback @func and pass to it as an argument each hash
 * item and the private @data. During the callback the bucket lock
 * is held so the callback must never sleep.
 */
void
cfs_hash_for_each_key(struct cfs_hash *hs, const void *key,
                      cfs_hash_for_each_cb_t func, void *data)
{
        struct hlist_node *hnode;
        struct cfs_hash_bd bds[2];
        unsigned int i;

        cfs_hash_lock(hs, 0);

        cfs_hash_dual_bd_get_and_lock(hs, key, bds, 0);

        cfs_hash_for_each_bd(bds, 2, i) {
                struct hlist_head *hlist = cfs_hash_bd_hhead(hs, &bds[i]);

                hlist_for_each(hnode, hlist) {
                        cfs_hash_bucket_validate(hs, &bds[i], hnode);

                        if (cfs_hash_keycmp(hs, key, hnode)) {
                                if (func(hs, &bds[i], hnode, data))
                                        break;
                        }
                }
        }

        cfs_hash_dual_bd_unlock(hs, bds, 0);
        cfs_hash_unlock(hs, 0);
}
EXPORT_SYMBOL(cfs_hash_for_each_key);

/**
 * Rehash the libcfs hash @hs to the given @bits.  This can be used
 * to grow the hash size when excessive chaining is detected, or to
 * shrink the hash when it is larger than needed.  When the CFS_HASH_REHASH
 * flag is set in @hs the libcfs hash may be dynamically rehashed
 * during addition or removal if the hash's theta value exceeds
 * either the hs->hs_min_theta or hs->max_theta values.  By default
 * these values are tuned to keep the chained hash depth small, and
 * this approach assumes a reasonably uniform hashing function.  The
 * theta thresholds for @hs are tunable via cfs_hash_set_theta().
 */
void
cfs_hash_rehash_cancel_locked(struct cfs_hash *hs)
{
        int i;

        /* need hold cfs_hash_lock(hs, 1) */
        LASSERT(cfs_hash_with_rehash(hs) &&
                !cfs_hash_with_no_lock(hs));

        if (!cfs_hash_is_rehashing(hs))
                return;

        if (cfs_wi_deschedule(cfs_sched_rehash, &hs->hs_rehash_wi)) {
                hs->hs_rehash_bits = 0;
                return;
        }

        for (i = 2; cfs_hash_is_rehashing(hs); i++) {
                cfs_hash_unlock(hs, 1);
                /* raise console warning while waiting too long */
                CDEBUG(is_power_of_2(i >> 3) ? D_WARNING : D_INFO,
                       "hash %s is still rehashing, rescheded %d\n",
                       hs->hs_name, i - 1);
                cond_resched();
                cfs_hash_lock(hs, 1);
        }
}

void
cfs_hash_rehash_cancel(struct cfs_hash *hs)
{
        cfs_hash_lock(hs, 1);
        cfs_hash_rehash_cancel_locked(hs);
        cfs_hash_unlock(hs, 1);
}

int
cfs_hash_rehash(struct cfs_hash *hs, int do_rehash)
{
        int rc;

        LASSERT(cfs_hash_with_rehash(hs) && !cfs_hash_with_no_lock(hs));

        cfs_hash_lock(hs, 1);

        rc = cfs_hash_rehash_bits(hs);
        if (rc <= 0) {
                cfs_hash_unlock(hs, 1);
                return rc;
        }

        hs->hs_rehash_bits = rc;
        if (!do_rehash) {
                /* launch and return */
                cfs_wi_schedule(cfs_sched_rehash, &hs->hs_rehash_wi);
                cfs_hash_unlock(hs, 1);
                return 0;
        }

        /* rehash right now */
        cfs_hash_unlock(hs, 1);

        return cfs_hash_rehash_worker(&hs->hs_rehash_wi);
}

static int
cfs_hash_rehash_bd(struct cfs_hash *hs, struct cfs_hash_bd *old)
{
        struct cfs_hash_bd new;
        struct hlist_head *hhead;
        struct hlist_node *hnode;
        struct hlist_node *pos;
        void *key;
        int c = 0;

        /* hold cfs_hash_lock(hs, 1), so don't need any bucket lock */
        cfs_hash_bd_for_each_hlist(hs, old, hhead) {
                hlist_for_each_safe(hnode, pos, hhead) {
                        key = cfs_hash_key(hs, hnode);
                        LASSERT(key);
                        /* Validate hnode is in the correct bucket. */
                        cfs_hash_bucket_validate(hs, old, hnode);
                        /*
                         * Delete from old hash bucket; move to new bucket.
                         * ops->hs_key must be defined.
                         */
                        cfs_hash_bd_from_key(hs, hs->hs_rehash_buckets,
                                             hs->hs_rehash_bits, key, &new);
                        cfs_hash_bd_move_locked(hs, old, &new, hnode);
                        c++;
                }
        }

        return c;
}

static int
cfs_hash_rehash_worker(struct cfs_workitem *wi)
{
        struct cfs_hash *hs = container_of(wi, struct cfs_hash, hs_rehash_wi);
        struct cfs_hash_bucket **bkts;
        struct cfs_hash_bd bd;
        unsigned int old_size;
        unsigned int new_size;
        int bsize;
        int count = 0;
        int rc = 0;
        int i;

        LASSERT(hs && cfs_hash_with_rehash(hs));

        cfs_hash_lock(hs, 0);
        LASSERT(cfs_hash_is_rehashing(hs));

        old_size = CFS_HASH_NBKT(hs);
        new_size = CFS_HASH_RH_NBKT(hs);

        cfs_hash_unlock(hs, 0);

        /*
         * don't need hs::hs_rwlock for hs::hs_buckets,
         * because nobody can change bkt-table except me.
         */
        bkts = cfs_hash_buckets_realloc(hs, hs->hs_buckets,
                                        old_size, new_size);
        cfs_hash_lock(hs, 1);
        if (!bkts) {
                rc = -ENOMEM;
                goto out;
        }

        if (bkts == hs->hs_buckets) {
                bkts = NULL; /* do nothing */
                goto out;
        }

        rc = __cfs_hash_theta(hs);
        if ((rc >= hs->hs_min_theta) && (rc <= hs->hs_max_theta)) {
                /* free the new allocated bkt-table */
                old_size = new_size;
                new_size = CFS_HASH_NBKT(hs);
                rc = -EALREADY;
                goto out;
        }

        LASSERT(!hs->hs_rehash_buckets);
        hs->hs_rehash_buckets = bkts;

        rc = 0;
        cfs_hash_for_each_bucket(hs, &bd, i) {
                if (cfs_hash_is_exiting(hs)) {
                        rc = -ESRCH;
                        /* someone wants to destroy the hash, abort now */
                        if (old_size < new_size) /* OK to free old bkt-table */
                                break;
                        /* it's shrinking, need free new bkt-table */
                        hs->hs_rehash_buckets = NULL;
                        old_size = new_size;
                        new_size = CFS_HASH_NBKT(hs);
                        goto out;
                }

                count += cfs_hash_rehash_bd(hs, &bd);
                if (count < CFS_HASH_LOOP_HOG ||
                    cfs_hash_is_iterating(hs)) { /* need to finish ASAP */
                        continue;
                }

                count = 0;
                cfs_hash_unlock(hs, 1);
                cond_resched();
                cfs_hash_lock(hs, 1);
        }

        hs->hs_rehash_count++;

        bkts = hs->hs_buckets;
        hs->hs_buckets = hs->hs_rehash_buckets;
        hs->hs_rehash_buckets = NULL;

        hs->hs_cur_bits = hs->hs_rehash_bits;
out:
        hs->hs_rehash_bits = 0;
        if (rc == -ESRCH) /* never be scheduled again */
                cfs_wi_exit(cfs_sched_rehash, wi);
        bsize = cfs_hash_bkt_size(hs);
        cfs_hash_unlock(hs, 1);
        /* can't refer to @hs anymore because it could be destroyed */
        if (bkts)
                cfs_hash_buckets_free(bkts, bsize, new_size, old_size);
        if (rc)
                CDEBUG(D_INFO, "early quit of rehashing: %d\n", rc);
        /* return 1 only if cfs_wi_exit is called */
        return rc == -ESRCH;
}

/**
 * Rehash the object referenced by @hnode in the libcfs hash @hs.  The
 * @old_key must be provided to locate the objects previous location
 * in the hash, and the @new_key will be used to reinsert the object.
 * Use this function instead of a cfs_hash_add() + cfs_hash_del()
 * combo when it is critical that there is no window in time where the
 * object is missing from the hash.  When an object is being rehashed
 * the registered cfs_hash_get() and cfs_hash_put() functions will
 * not be called.
 */
void cfs_hash_rehash_key(struct cfs_hash *hs, const void *old_key,
                         void *new_key, struct hlist_node *hnode)
{
        struct cfs_hash_bd bds[3];
        struct cfs_hash_bd old_bds[2];
        struct cfs_hash_bd new_bd;

        LASSERT(!hlist_unhashed(hnode));

        cfs_hash_lock(hs, 0);

        cfs_hash_dual_bd_get(hs, old_key, old_bds);
        cfs_hash_bd_get(hs, new_key, &new_bd);

        bds[0] = old_bds[0];
        bds[1] = old_bds[1];
        bds[2] = new_bd;

        /* NB: bds[0] and bds[1] are ordered already */
        cfs_hash_bd_order(&bds[1], &bds[2]);
        cfs_hash_bd_order(&bds[0], &bds[1]);

        cfs_hash_multi_bd_lock(hs, bds, 3, 1);
        if (likely(!old_bds[1].bd_bucket)) {
                cfs_hash_bd_move_locked(hs, &old_bds[0], &new_bd, hnode);
        } else {
                cfs_hash_dual_bd_finddel_locked(hs, old_bds, old_key, hnode);
                cfs_hash_bd_add_locked(hs, &new_bd, hnode);
        }
        /* overwrite key inside locks, otherwise may screw up with
         * other operations, i.e: rehash
         */
        cfs_hash_keycpy(hs, hnode, new_key);

        cfs_hash_multi_bd_unlock(hs, bds, 3, 1);
        cfs_hash_unlock(hs, 0);
}
EXPORT_SYMBOL(cfs_hash_rehash_key);

void cfs_hash_debug_header(struct seq_file *m)
{
        seq_printf(m, "%-*s   cur   min   max theta t-min t-max flags rehash   count  maxdep maxdepb distribution\n",
                   CFS_HASH_BIGNAME_LEN, "name");
}
EXPORT_SYMBOL(cfs_hash_debug_header);

static struct cfs_hash_bucket **
cfs_hash_full_bkts(struct cfs_hash *hs)
{
        /* NB: caller should hold hs->hs_rwlock if REHASH is set */
        if (!hs->hs_rehash_buckets)
                return hs->hs_buckets;

        LASSERT(hs->hs_rehash_bits);
        return hs->hs_rehash_bits > hs->hs_cur_bits ?
               hs->hs_rehash_buckets : hs->hs_buckets;
}

static unsigned int
cfs_hash_full_nbkt(struct cfs_hash *hs)
{
        /* NB: caller should hold hs->hs_rwlock if REHASH is set */
        if (!hs->hs_rehash_buckets)
                return CFS_HASH_NBKT(hs);

        LASSERT(hs->hs_rehash_bits);
        return hs->hs_rehash_bits > hs->hs_cur_bits ?
               CFS_HASH_RH_NBKT(hs) : CFS_HASH_NBKT(hs);
}

void cfs_hash_debug_str(struct cfs_hash *hs, struct seq_file *m)
{
        int dist[8] = { 0, };
        int maxdep = -1;
        int maxdepb = -1;
        int total = 0;
        int theta;
        int i;

        cfs_hash_lock(hs, 0);
        theta = __cfs_hash_theta(hs);

        seq_printf(m, "%-*s %5d %5d %5d %d.%03d %d.%03d %d.%03d  0x%02x %6d ",
                   CFS_HASH_BIGNAME_LEN, hs->hs_name,
                   1 << hs->hs_cur_bits, 1 << hs->hs_min_bits,
                   1 << hs->hs_max_bits,
                   __cfs_hash_theta_int(theta), __cfs_hash_theta_frac(theta),
                   __cfs_hash_theta_int(hs->hs_min_theta),
                   __cfs_hash_theta_frac(hs->hs_min_theta),
                   __cfs_hash_theta_int(hs->hs_max_theta),
                   __cfs_hash_theta_frac(hs->hs_max_theta),
                   hs->hs_flags, hs->hs_rehash_count);

        /*
         * The distribution is a summary of the chained hash depth in
         * each of the libcfs hash buckets.  Each buckets hsb_count is
         * divided by the hash theta value and used to generate a
         * histogram of the hash distribution.  A uniform hash will
         * result in all hash buckets being close to the average thus
         * only the first few entries in the histogram will be non-zero.
         * If you hash function results in a non-uniform hash the will
         * be observable by outlier bucks in the distribution histogram.
         *
         * Uniform hash distribution:           128/128/0/0/0/0/0/0
         * Non-Uniform hash distribution:       128/125/0/0/0/0/2/1
         */
        for (i = 0; i < cfs_hash_full_nbkt(hs); i++) {
                struct cfs_hash_bd bd;

                bd.bd_bucket = cfs_hash_full_bkts(hs)[i];
                cfs_hash_bd_lock(hs, &bd, 0);
                if (maxdep < bd.bd_bucket->hsb_depmax) {
                        maxdep  = bd.bd_bucket->hsb_depmax;
                        maxdepb = ffz(~maxdep);
                }
                total += bd.bd_bucket->hsb_count;
                dist[min(fls(bd.bd_bucket->hsb_count / max(theta, 1)), 7)]++;
                cfs_hash_bd_unlock(hs, &bd, 0);
        }

        seq_printf(m, "%7d %7d %7d ", total, maxdep, maxdepb);
        for (i = 0; i < 8; i++)
                seq_printf(m, "%d%c",  dist[i], (i == 7) ? '\n' : '/');

        cfs_hash_unlock(hs, 0);
}
EXPORT_SYMBOL(cfs_hash_debug_str);