[userspace-rcu.git] / rcuja / rcuja.c

/*
 * rcuja/rcuja.c
 *
 * Userspace RCU library - RCU Judy Array
 *
 * Copyright 2012 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

#define _LGPL_SOURCE
#include <stdint.h>
#include <errno.h>
#include <limits.h>
#include <string.h>
#include <urcu/rcuja.h>
#include <urcu/compiler.h>
#include <urcu/arch.h>
#include <assert.h>
#include <urcu-pointer.h>
#include <urcu/uatomic.h>
#include <stdint.h>

#include "rcuja-internal.h"
#include "bitfield.h"

#ifndef abs
#define abs_int(a)      ((int) (a) > 0 ? (int) (a) : -((int) (a)))
#endif

enum cds_ja_type_class {
        RCU_JA_LINEAR = 0,      /* Type A */
                        /* 32-bit: 1 to 25 children, 8 to 128 bytes */
                        /* 64-bit: 1 to 28 children, 16 to 256 bytes */
        RCU_JA_POOL = 1,        /* Type B */
                        /* 32-bit: 26 to 100 children, 256 to 512 bytes */
                        /* 64-bit: 29 to 112 children, 512 to 1024 bytes */
        RCU_JA_PIGEON = 2,      /* Type C */
                        /* 32-bit: 101 to 256 children, 1024 bytes */
                        /* 64-bit: 113 to 256 children, 2048 bytes */
        /* Leaf nodes are implicit from their height in the tree */
        RCU_JA_NR_TYPES,

        RCU_JA_NULL,    /* not an encoded type, but keeps code regular */
};

struct cds_ja_type {
        enum cds_ja_type_class type_class;
        uint16_t min_child;             /* minimum number of children: 1 to 256 */
        uint16_t max_child;             /* maximum number of children: 1 to 256 */
        uint16_t max_linear_child;      /* per-pool max nr. children: 1 to 256 */
        uint16_t order;                 /* node size is (1 << order), in bytes */
        uint16_t nr_pool_order;         /* number of pools */
        uint16_t pool_size_order;       /* pool size */
};

/*
 * Iteration on the array to find the right node size for the number of
 * children stops when it reaches .max_child == 256 (this is the largest
 * possible node size, which contains 256 children).
 * The min_child overlaps with the previous max_child to provide an
 * hysteresis loop to reallocation for patterns of cyclic add/removal
 * within the same node.
 * The node the index within the following arrays is represented on 3
 * bits. It identifies the node type, min/max number of children, and
 * the size order.
 * The max_child values for the RCU_JA_POOL below result from
 * statistical approximation: over million populations, the max_child
 * covers between 97% and 99% of the populations generated. Therefore, a
 * fallback should exist to cover the rare extreme population unbalance
 * cases, but it will not have a major impact on speed nor space
 * consumption, since those are rare cases.
 */

#if (CAA_BITS_PER_LONG < 64)
/* 32-bit pointers */
enum {
        ja_type_0_max_child = 1,
        ja_type_1_max_child = 3,
        ja_type_2_max_child = 6,
        ja_type_3_max_child = 12,
        ja_type_4_max_child = 25,
        ja_type_5_max_child = 48,
        ja_type_6_max_child = 92,
        ja_type_7_max_child = 256,
        ja_type_8_max_child = 0,        /* NULL */
};

enum {
        ja_type_0_max_linear_child = 1,
        ja_type_1_max_linear_child = 3,
        ja_type_2_max_linear_child = 6,
        ja_type_3_max_linear_child = 12,
        ja_type_4_max_linear_child = 25,
        ja_type_5_max_linear_child = 24,
        ja_type_6_max_linear_child = 23,
};

enum {
        ja_type_5_nr_pool_order = 1,
        ja_type_6_nr_pool_order = 2,
};

const struct cds_ja_type ja_types[] = {
        { .type_class = RCU_JA_LINEAR, .min_child = 1, .max_child = ja_type_0_max_child, .max_linear_child = ja_type_0_max_linear_child, .order = 3, },
        { .type_class = RCU_JA_LINEAR, .min_child = 1, .max_child = ja_type_1_max_child, .max_linear_child = ja_type_1_max_linear_child, .order = 4, },
        { .type_class = RCU_JA_LINEAR, .min_child = 3, .max_child = ja_type_2_max_child, .max_linear_child = ja_type_2_max_linear_child, .order = 5, },
        { .type_class = RCU_JA_LINEAR, .min_child = 4, .max_child = ja_type_3_max_child, .max_linear_child = ja_type_3_max_linear_child, .order = 6, },
        { .type_class = RCU_JA_LINEAR, .min_child = 10, .max_child = ja_type_4_max_child, .max_linear_child = ja_type_4_max_linear_child, .order = 7, },

        /* Pools may fill sooner than max_child */
        { .type_class = RCU_JA_POOL, .min_child = 20, .max_child = ja_type_5_max_child, .max_linear_child = ja_type_5_max_linear_child, .order = 8, .nr_pool_order = ja_type_5_nr_pool_order, .pool_size_order = 7, },
        { .type_class = RCU_JA_POOL, .min_child = 45, .max_child = ja_type_6_max_child, .max_linear_child = ja_type_6_max_linear_child, .order = 9, .nr_pool_order = ja_type_6_nr_pool_order, .pool_size_order = 7, },

        /*
         * Upon node removal below min_child, if child pool is filled
         * beyond capacity, we roll back to pigeon.
         */
        { .type_class = RCU_JA_PIGEON, .min_child = 83, .max_child = ja_type_7_max_child, .order = 10, },

        { .type_class = RCU_JA_NULL, .min_child = 0, .max_child = ja_type_8_max_child, },
};
#else /* !(CAA_BITS_PER_LONG < 64) */
/* 64-bit pointers */
enum {
        ja_type_0_max_child = 1,
        ja_type_1_max_child = 3,
        ja_type_2_max_child = 7,
        ja_type_3_max_child = 14,
        ja_type_4_max_child = 28,
        ja_type_5_max_child = 54,
        ja_type_6_max_child = 104,
        ja_type_7_max_child = 256,
        ja_type_8_max_child = 256,
};

enum {
        ja_type_0_max_linear_child = 1,
        ja_type_1_max_linear_child = 3,
        ja_type_2_max_linear_child = 7,
        ja_type_3_max_linear_child = 14,
        ja_type_4_max_linear_child = 28,
        ja_type_5_max_linear_child = 27,
        ja_type_6_max_linear_child = 26,
};

enum {
        ja_type_5_nr_pool_order = 1,
        ja_type_6_nr_pool_order = 2,
};

const struct cds_ja_type ja_types[] = {
        { .type_class = RCU_JA_LINEAR, .min_child = 1, .max_child = ja_type_0_max_child, .max_linear_child = ja_type_0_max_linear_child, .order = 4, },
        { .type_class = RCU_JA_LINEAR, .min_child = 1, .max_child = ja_type_1_max_child, .max_linear_child = ja_type_1_max_linear_child, .order = 5, },
        { .type_class = RCU_JA_LINEAR, .min_child = 3, .max_child = ja_type_2_max_child, .max_linear_child = ja_type_2_max_linear_child, .order = 6, },
        { .type_class = RCU_JA_LINEAR, .min_child = 5, .max_child = ja_type_3_max_child, .max_linear_child = ja_type_3_max_linear_child, .order = 7, },
        { .type_class = RCU_JA_LINEAR, .min_child = 10, .max_child = ja_type_4_max_child, .max_linear_child = ja_type_4_max_linear_child, .order = 8, },

        /* Pools may fill sooner than max_child. */
        { .type_class = RCU_JA_POOL, .min_child = 22, .max_child = ja_type_5_max_child, .max_linear_child = ja_type_5_max_linear_child, .order = 9, .nr_pool_order = ja_type_5_nr_pool_order, .pool_size_order = 8, },
        { .type_class = RCU_JA_POOL, .min_child = 51, .max_child = ja_type_6_max_child, .max_linear_child = ja_type_6_max_linear_child, .order = 10, .nr_pool_order = ja_type_6_nr_pool_order, .pool_size_order = 8, },

        /*
         * Upon node removal below min_child, if child pool is filled
         * beyond capacity, we roll back to pigeon.
         */
        { .type_class = RCU_JA_PIGEON, .min_child = 95, .max_child = ja_type_7_max_child, .order = 11, },

        { .type_class = RCU_JA_NULL, .min_child = 0, .max_child = ja_type_8_max_child, },
};
#endif /* !(BITS_PER_LONG < 64) */

static inline __attribute__((unused))
void static_array_size_check(void)
{
        CAA_BUILD_BUG_ON(CAA_ARRAY_SIZE(ja_types) < JA_TYPE_MAX_NR);
}

/*
 * The cds_ja_node contains the compressed node data needed for
 * read-side. For linear and pool node configurations, it starts with a
 * byte counting the number of children in the node.  Then, the
 * node-specific data is placed.
 * The node mutex, if any is needed, protecting concurrent updated of
 * each node is placed in a separate hash table indexed by node address.
 * For the pigeon configuration, the number of children is also kept in
 * a separate hash table, indexed by node address, because it is only
 * required for updates.
 */

#define DECLARE_LINEAR_NODE(index)                                                              \
        struct {                                                                                \
                uint8_t nr_child;                                                               \
                uint8_t child_value[ja_type_## index ##_max_linear_child];                      \
                struct cds_ja_inode_flag *child_ptr[ja_type_## index ##_max_linear_child];      \
        }

#define DECLARE_POOL_NODE(index)                                                                \
        struct {                                                                                \
                struct {                                                                        \
                        uint8_t nr_child;                                                       \
                        uint8_t child_value[ja_type_## index ##_max_linear_child];              \
                        struct cds_ja_inode_flag *child_ptr[ja_type_## index ##_max_linear_child]; \
                } linear[1U << ja_type_## index ##_nr_pool_order];                              \
        }

struct cds_ja_inode {
        union {
                /* Linear configuration */
                DECLARE_LINEAR_NODE(0) conf_0;
                DECLARE_LINEAR_NODE(1) conf_1;
                DECLARE_LINEAR_NODE(2) conf_2;
                DECLARE_LINEAR_NODE(3) conf_3;
                DECLARE_LINEAR_NODE(4) conf_4;

                /* Pool configuration */
                DECLARE_POOL_NODE(5) conf_5;
                DECLARE_POOL_NODE(6) conf_6;

                /* Pigeon configuration */
                struct {
                        struct cds_ja_inode_flag *child[ja_type_7_max_child];
                } conf_7;
                /* data aliasing nodes for computed accesses */
                uint8_t data[sizeof(struct cds_ja_inode_flag *) * ja_type_7_max_child];
        } u;
};

enum ja_recompact {
        JA_RECOMPACT_ADD_SAME,
        JA_RECOMPACT_ADD_NEXT,
        JA_RECOMPACT_DEL,
};

static
struct cds_ja_inode *_ja_node_mask_ptr(struct cds_ja_inode_flag *node)
{
        return (struct cds_ja_inode *) (((unsigned long) node) & JA_PTR_MASK);
}

unsigned long ja_node_type(struct cds_ja_inode_flag *node)
{
        unsigned long type;

        if (_ja_node_mask_ptr(node) == NULL) {
                return NODE_INDEX_NULL;
        }
        type = (unsigned int) ((unsigned long) node & JA_TYPE_MASK);
        assert(type < (1UL << JA_TYPE_BITS));
        return type;
}

struct cds_ja_inode *ja_node_ptr(struct cds_ja_inode_flag *node)
{
        unsigned long type_index = ja_node_type(node);
        const struct cds_ja_type *type;

        type = &ja_types[type_index];
        switch (type->type_class) {
        case RCU_JA_LINEAR:
        case RCU_JA_PIGEON:     /* fall-through */
        case RCU_JA_NULL:       /* fall-through */
        default:                /* fall-through */
                return _ja_node_mask_ptr(node);
        case RCU_JA_POOL:
                switch (type->nr_pool_order) {
                case 1:
                        return (struct cds_ja_inode *) (((unsigned long) node) & ~(JA_POOL_1D_MASK | JA_TYPE_MASK));
                case 2:
                        return (struct cds_ja_inode *) (((unsigned long) node) & ~(JA_POOL_2D_MASK | JA_POOL_1D_MASK | JA_TYPE_MASK));
                default:
                        assert(0);
                }
        }
}

static
struct cds_ja_inode *alloc_cds_ja_node(struct cds_ja *ja,
                const struct cds_ja_type *ja_type)
{
        size_t len = 1U << ja_type->order;
        void *p;
        int ret;

        ret = posix_memalign(&p, len, len);
        if (ret || !p) {
                return NULL;
        }
        memset(p, 0, len);
        uatomic_inc(&ja->nr_nodes_allocated);
        return p;
}

void free_cds_ja_node(struct cds_ja *ja, struct cds_ja_inode *node)
{
        free(node);
        if (node)
                uatomic_inc(&ja->nr_nodes_freed);
}

#define __JA_ALIGN_MASK(v, mask)        (((v) + (mask)) & ~(mask))
#define JA_ALIGN(v, align)              __JA_ALIGN_MASK(v, (typeof(v)) (align) - 1)
#define __JA_FLOOR_MASK(v, mask)        ((v) & ~(mask))
#define JA_FLOOR(v, align)              __JA_FLOOR_MASK(v, (typeof(v)) (align) - 1)

static
uint8_t *align_ptr_size(uint8_t *ptr)
{
        return (uint8_t *) JA_ALIGN((unsigned long) ptr, sizeof(void *));
}

static
uint8_t ja_linear_node_get_nr_child(const struct cds_ja_type *type,
                struct cds_ja_inode *node)
{
        assert(type->type_class == RCU_JA_LINEAR || type->type_class == RCU_JA_POOL);
        return rcu_dereference(node->u.data[0]);
}

/*
 * The order in which values and pointers are does does not matter: if
 * a value is missing, we return NULL. If a value is there, but its
 * associated pointers is still NULL, we return NULL too.
 */
static
struct cds_ja_inode_flag *ja_linear_node_get_nth(const struct cds_ja_type *type,
                struct cds_ja_inode *node,
                struct cds_ja_inode_flag ***node_flag_ptr,
                uint8_t n)
{
        uint8_t nr_child;
        uint8_t *values;
        struct cds_ja_inode_flag **pointers;
        struct cds_ja_inode_flag *ptr;
        unsigned int i;

        assert(type->type_class == RCU_JA_LINEAR || type->type_class == RCU_JA_POOL);

        nr_child = ja_linear_node_get_nr_child(type, node);
        cmm_smp_rmb();  /* read nr_child before values and pointers */
        assert(nr_child <= type->max_linear_child);
        assert(type->type_class != RCU_JA_LINEAR || nr_child >= type->min_child);

        values = &node->u.data[1];
        for (i = 0; i < nr_child; i++) {
                if (CMM_LOAD_SHARED(values[i]) == n)
                        break;
        }
        if (i >= nr_child) {
                if (caa_unlikely(node_flag_ptr))
                        *node_flag_ptr = NULL;
                return NULL;
        }
        pointers = (struct cds_ja_inode_flag **) align_ptr_size(&values[type->max_linear_child]);
        ptr = rcu_dereference(pointers[i]);
        if (caa_unlikely(node_flag_ptr))
                *node_flag_ptr = &pointers[i];
        return ptr;
}

static
void ja_linear_node_get_ith_pos(const struct cds_ja_type *type,
                struct cds_ja_inode *node,
                uint8_t i,
                uint8_t *v,
                struct cds_ja_inode_flag **iter)
{
        uint8_t *values;
        struct cds_ja_inode_flag **pointers;

        assert(type->type_class == RCU_JA_LINEAR || type->type_class == RCU_JA_POOL);
        assert(i < ja_linear_node_get_nr_child(type, node));

        values = &node->u.data[1];
        *v = values[i];
        pointers = (struct cds_ja_inode_flag **) align_ptr_size(&values[type->max_linear_child]);
        *iter = pointers[i];
}

static
struct cds_ja_inode_flag *ja_pool_node_get_nth(const struct cds_ja_type *type,
                struct cds_ja_inode *node,
                struct cds_ja_inode_flag *node_flag,
                struct cds_ja_inode_flag ***node_flag_ptr,
                uint8_t n)
{
        struct cds_ja_inode *linear;

        assert(type->type_class == RCU_JA_POOL);

        switch (type->nr_pool_order) {
        case 1:
        {
                unsigned long bitsel, index;

                bitsel = ja_node_pool_1d_bitsel(node_flag);
                assert(bitsel < CHAR_BIT);
                index = ((unsigned long) n >> bitsel) & 0x1;
                linear = (struct cds_ja_inode *) &node->u.data[index << type->pool_size_order];
                break;
        }
        case 2:
        {
                unsigned long bitsel[2], index[2], rindex;

                ja_node_pool_2d_bitsel(node_flag, bitsel);
                assert(bitsel[0] < CHAR_BIT);
                assert(bitsel[1] < CHAR_BIT);
                index[0] = ((unsigned long) n >> bitsel[0]) & 0x1;
                index[0] <<= 1;
                index[1] = ((unsigned long) n >> bitsel[1]) & 0x1;
                rindex = index[0] | index[1];
                linear = (struct cds_ja_inode *) &node->u.data[rindex << type->pool_size_order];
                break;
        }
        default:
                linear = NULL;
                assert(0);
        }
        return ja_linear_node_get_nth(type, linear, node_flag_ptr, n);
}

static
struct cds_ja_inode *ja_pool_node_get_ith_pool(const struct cds_ja_type *type,
                struct cds_ja_inode *node,
                uint8_t i)
{
        assert(type->type_class == RCU_JA_POOL);
        return (struct cds_ja_inode *)
                &node->u.data[(unsigned int) i << type->pool_size_order];
}

static
struct cds_ja_inode_flag *ja_pigeon_node_get_nth(const struct cds_ja_type *type,
                struct cds_ja_inode *node,
                struct cds_ja_inode_flag ***node_flag_ptr,
                uint8_t n)
{
        struct cds_ja_inode_flag **child_node_flag_ptr;
        struct cds_ja_inode_flag *child_node_flag;

        assert(type->type_class == RCU_JA_PIGEON);
        child_node_flag_ptr = &((struct cds_ja_inode_flag **) node->u.data)[n];
        child_node_flag = rcu_dereference(*child_node_flag_ptr);
        dbg_printf("ja_pigeon_node_get_nth child_node_flag_ptr %p\n",
                child_node_flag_ptr);
        if (caa_unlikely(node_flag_ptr))
                *node_flag_ptr = child_node_flag_ptr;
        return child_node_flag;
}

static
struct cds_ja_inode_flag *ja_pigeon_node_get_ith_pos(const struct cds_ja_type *type,
                struct cds_ja_inode *node,
                uint8_t i)
{
        return ja_pigeon_node_get_nth(type, node, NULL, i);
}

/*
 * ja_node_get_nth: get nth item from a node.
 * node_flag is already rcu_dereference'd.
 */
static
struct cds_ja_inode_flag *ja_node_get_nth(struct cds_ja_inode_flag *node_flag,
                struct cds_ja_inode_flag ***node_flag_ptr,
                uint8_t n)
{
        unsigned int type_index;
        struct cds_ja_inode *node;
        const struct cds_ja_type *type;

        node = ja_node_ptr(node_flag);
        assert(node != NULL);
        type_index = ja_node_type(node_flag);
        type = &ja_types[type_index];

        switch (type->type_class) {
        case RCU_JA_LINEAR:
                return ja_linear_node_get_nth(type, node,
                                node_flag_ptr, n);
        case RCU_JA_POOL:
                return ja_pool_node_get_nth(type, node, node_flag,
                                node_flag_ptr, n);
        case RCU_JA_PIGEON:
                return ja_pigeon_node_get_nth(type, node,
                                node_flag_ptr, n);
        default:
                assert(0);
                return (void *) -1UL;
        }
}

static
int ja_linear_node_set_nth(const struct cds_ja_type *type,
                struct cds_ja_inode *node,
                struct cds_ja_shadow_node *shadow_node,
                uint8_t n,
                struct cds_ja_inode_flag *child_node_flag)
{
        uint8_t nr_child;
        uint8_t *values, *nr_child_ptr;
        struct cds_ja_inode_flag **pointers;
        unsigned int i, unused = 0;

        assert(type->type_class == RCU_JA_LINEAR || type->type_class == RCU_JA_POOL);

        nr_child_ptr = &node->u.data[0];
        dbg_printf("linear set nth: n %u, nr_child_ptr %p\n",
                (unsigned int) n, nr_child_ptr);
        nr_child = *nr_child_ptr;
        assert(nr_child <= type->max_linear_child);

        values = &node->u.data[1];
        pointers = (struct cds_ja_inode_flag **) align_ptr_size(&values[type->max_linear_child]);
        /* Check if node value is already populated */
        for (i = 0; i < nr_child; i++) {
                if (values[i] == n) {
                        if (pointers[i])
                                return -EEXIST;
                        else
                                break;
                } else {
                        if (!pointers[i])
                                unused++;
                }
        }
        if (i == nr_child && nr_child >= type->max_linear_child) {
                if (unused)
                        return -ERANGE; /* recompact node */
                else
                        return -ENOSPC; /* No space left in this node type */
        }

        assert(pointers[i] == NULL);
        rcu_assign_pointer(pointers[i], child_node_flag);
        /* If we expanded the nr_child, increment it */
        if (i == nr_child) {
                CMM_STORE_SHARED(values[nr_child], n);
                /* write pointer and value before nr_child */
                cmm_smp_wmb();
                CMM_STORE_SHARED(*nr_child_ptr, nr_child + 1);
        }
        shadow_node->nr_child++;
        dbg_printf("linear set nth: %u child, shadow: %u child, for node %p shadow %p\n",
                (unsigned int) CMM_LOAD_SHARED(*nr_child_ptr),
                (unsigned int) shadow_node->nr_child,
                node, shadow_node);

        return 0;
}

static
int ja_pool_node_set_nth(const struct cds_ja_type *type,
                struct cds_ja_inode *node,
                struct cds_ja_inode_flag *node_flag,
                struct cds_ja_shadow_node *shadow_node,
                uint8_t n,
                struct cds_ja_inode_flag *child_node_flag)
{
        struct cds_ja_inode *linear;

        assert(type->type_class == RCU_JA_POOL);

        switch (type->nr_pool_order) {
        case 1:
        {
                unsigned long bitsel, index;

                bitsel = ja_node_pool_1d_bitsel(node_flag);
                assert(bitsel < CHAR_BIT);
                index = ((unsigned long) n >> bitsel) & 0x1;
                linear = (struct cds_ja_inode *) &node->u.data[index << type->pool_size_order];
                break;
        }
        case 2:
        {
                unsigned long bitsel[2], index[2], rindex;

                ja_node_pool_2d_bitsel(node_flag, bitsel);
                assert(bitsel[0] < CHAR_BIT);
                assert(bitsel[1] < CHAR_BIT);
                index[0] = ((unsigned long) n >> bitsel[0]) & 0x1;
                index[0] <<= 1;
                index[1] = ((unsigned long) n >> bitsel[1]) & 0x1;
                rindex = index[0] | index[1];
                linear = (struct cds_ja_inode *) &node->u.data[rindex << type->pool_size_order];
                break;
        }
        default:
                linear = NULL;
                assert(0);
        }

        return ja_linear_node_set_nth(type, linear, shadow_node,
                        n, child_node_flag);
}

static
int ja_pigeon_node_set_nth(const struct cds_ja_type *type,
                struct cds_ja_inode *node,
                struct cds_ja_shadow_node *shadow_node,
                uint8_t n,
                struct cds_ja_inode_flag *child_node_flag)
{
        struct cds_ja_inode_flag **ptr;

        assert(type->type_class == RCU_JA_PIGEON);
        ptr = &((struct cds_ja_inode_flag **) node->u.data)[n];
        if (*ptr)
                return -EEXIST;
        rcu_assign_pointer(*ptr, child_node_flag);
        shadow_node->nr_child++;
        return 0;
}

/*
 * _ja_node_set_nth: set nth item within a node. Return an error
 * (negative error value) if it is already there.
 */
static
int _ja_node_set_nth(const struct cds_ja_type *type,
                struct cds_ja_inode *node,
                struct cds_ja_inode_flag *node_flag,
                struct cds_ja_shadow_node *shadow_node,
                uint8_t n,
                struct cds_ja_inode_flag *child_node_flag)
{
        switch (type->type_class) {
        case RCU_JA_LINEAR:
                return ja_linear_node_set_nth(type, node, shadow_node, n,
                                child_node_flag);
        case RCU_JA_POOL:
                return ja_pool_node_set_nth(type, node, node_flag, shadow_node, n,
                                child_node_flag);
        case RCU_JA_PIGEON:
                return ja_pigeon_node_set_nth(type, node, shadow_node, n,
                                child_node_flag);
        case RCU_JA_NULL:
                return -ENOSPC;
        default:
                assert(0);
                return -EINVAL;
        }

        return 0;
}

static
int ja_linear_node_clear_ptr(const struct cds_ja_type *type,
                struct cds_ja_inode *node,
                struct cds_ja_shadow_node *shadow_node,
                struct cds_ja_inode_flag **node_flag_ptr)
{
        uint8_t nr_child;
        uint8_t *nr_child_ptr;

        assert(type->type_class == RCU_JA_LINEAR || type->type_class == RCU_JA_POOL);

        nr_child_ptr = &node->u.data[0];
        nr_child = *nr_child_ptr;
        assert(nr_child <= type->max_linear_child);

        if (type->type_class == RCU_JA_LINEAR) {
                assert(!shadow_node->fallback_removal_count);
                if (shadow_node->nr_child <= type->min_child) {
                        /* We need to try recompacting the node */
                        return -EFBIG;
                }
        }
        dbg_printf("linear clear ptr: nr_child_ptr %p\n", nr_child_ptr);
        assert(*node_flag_ptr != NULL);
        rcu_assign_pointer(*node_flag_ptr, NULL);
        /*
         * Value and nr_child are never changed (would cause ABA issue).
         * Instead, we leave the pointer to NULL and recompact the node
         * once in a while. It is allowed to set a NULL pointer to a new
         * value without recompaction though.
         * Only update the shadow node accounting.
         */
        shadow_node->nr_child--;
        dbg_printf("linear clear ptr: %u child, shadow: %u child, for node %p shadow %p\n",
                (unsigned int) CMM_LOAD_SHARED(*nr_child_ptr),
                (unsigned int) shadow_node->nr_child,
                node, shadow_node);
        return 0;
}

static
int ja_pool_node_clear_ptr(const struct cds_ja_type *type,
                struct cds_ja_inode *node,
                struct cds_ja_inode_flag *node_flag,
                struct cds_ja_shadow_node *shadow_node,
                struct cds_ja_inode_flag **node_flag_ptr,
                uint8_t n)
{
        struct cds_ja_inode *linear;

        assert(type->type_class == RCU_JA_POOL);

        if (shadow_node->fallback_removal_count) {
                shadow_node->fallback_removal_count--;
        } else {
                /* We should try recompacting the node */
                if (shadow_node->nr_child <= type->min_child)
                        return -EFBIG;
        }

        switch (type->nr_pool_order) {
        case 1:
        {
                unsigned long bitsel, index;

                bitsel = ja_node_pool_1d_bitsel(node_flag);
                assert(bitsel < CHAR_BIT);
                index = ((unsigned long) n >> bitsel) & type->nr_pool_order;
                linear = (struct cds_ja_inode *) &node->u.data[index << type->pool_size_order];
                break;
        }
        case 2:
        {
                unsigned long bitsel[2], index[2], rindex;

                ja_node_pool_2d_bitsel(node_flag, bitsel);
                assert(bitsel[0] < CHAR_BIT);
                assert(bitsel[1] < CHAR_BIT);
                index[0] = ((unsigned long) n >> bitsel[0]) & 0x1;
                index[0] <<= 1;
                index[1] = ((unsigned long) n >> bitsel[1]) & 0x1;
                rindex = index[0] | index[1];
                linear = (struct cds_ja_inode *) &node->u.data[rindex << type->pool_size_order];
                break;
        }
        default:
                linear = NULL;
                assert(0);
        }

        return ja_linear_node_clear_ptr(type, linear, shadow_node, node_flag_ptr);
}

static
int ja_pigeon_node_clear_ptr(const struct cds_ja_type *type,
                struct cds_ja_inode *node,
                struct cds_ja_shadow_node *shadow_node,
                struct cds_ja_inode_flag **node_flag_ptr)
{
        assert(type->type_class == RCU_JA_PIGEON);

        if (shadow_node->fallback_removal_count) {
                shadow_node->fallback_removal_count--;
        } else {
                /* We should try recompacting the node */
                if (shadow_node->nr_child <= type->min_child)
                        return -EFBIG;
        }
        dbg_printf("ja_pigeon_node_clear_ptr: clearing ptr: %p\n", *node_flag_ptr);
        rcu_assign_pointer(*node_flag_ptr, NULL);
        shadow_node->nr_child--;
        return 0;
}

/*
 * _ja_node_clear_ptr: clear ptr item within a node. Return an error
 * (negative error value) if it is not found (-ENOENT).
 */
static
int _ja_node_clear_ptr(const struct cds_ja_type *type,
                struct cds_ja_inode *node,
                struct cds_ja_inode_flag *node_flag,
                struct cds_ja_shadow_node *shadow_node,
                struct cds_ja_inode_flag **node_flag_ptr,
                uint8_t n)
{
        switch (type->type_class) {
        case RCU_JA_LINEAR:
                return ja_linear_node_clear_ptr(type, node, shadow_node, node_flag_ptr);
        case RCU_JA_POOL:
                return ja_pool_node_clear_ptr(type, node, node_flag, shadow_node, node_flag_ptr, n);
        case RCU_JA_PIGEON:
                return ja_pigeon_node_clear_ptr(type, node, shadow_node, node_flag_ptr);
        case RCU_JA_NULL:
                return -ENOENT;
        default:
                assert(0);
                return -EINVAL;
        }

        return 0;
}

/*
 * Calculate bit distribution. Returns the bit (0 to 7) that splits the
 * distribution in two sub-distributions containing as much elements one
 * compared to the other.
 */
static
unsigned int ja_node_sum_distribution_1d(enum ja_recompact mode,
                struct cds_ja *ja,
                unsigned int type_index,
                const struct cds_ja_type *type,
                struct cds_ja_inode *node,
                struct cds_ja_shadow_node *shadow_node,
                uint8_t n,
                struct cds_ja_inode_flag *child_node_flag,
                struct cds_ja_inode_flag **nullify_node_flag_ptr)
{
        uint8_t nr_one[JA_BITS_PER_BYTE];
        unsigned int bitsel = 0, bit_i, overall_best_distance = UINT_MAX;
        unsigned int distrib_nr_child = 0;

        memset(nr_one, 0, sizeof(nr_one));

        switch (type->type_class) {
        case RCU_JA_LINEAR:
        {
                uint8_t nr_child =
                        ja_linear_node_get_nr_child(type, node);
                unsigned int i;

                for (i = 0; i < nr_child; i++) {
                        struct cds_ja_inode_flag *iter;
                        uint8_t v;

                        ja_linear_node_get_ith_pos(type, node, i, &v, &iter);
                        if (!iter)
                                continue;
                        if (mode == JA_RECOMPACT_DEL && *nullify_node_flag_ptr == iter)
                                continue;
                        for (bit_i = 0; bit_i < JA_BITS_PER_BYTE; bit_i++) {
                                if (v & (1U << bit_i))
                                        nr_one[bit_i]++;
                        }
                        distrib_nr_child++;
                }
                break;
        }
        case RCU_JA_POOL:
        {
                unsigned int pool_nr;

                for (pool_nr = 0; pool_nr < (1U << type->nr_pool_order); pool_nr++) {
                        struct cds_ja_inode *pool =
                                ja_pool_node_get_ith_pool(type,
                                        node, pool_nr);
                        uint8_t nr_child =
                                ja_linear_node_get_nr_child(type, pool);
                        unsigned int j;

                        for (j = 0; j < nr_child; j++) {
                                struct cds_ja_inode_flag *iter;
                                uint8_t v;

                                ja_linear_node_get_ith_pos(type, pool,
                                                j, &v, &iter);
                                if (!iter)
                                        continue;
                                if (mode == JA_RECOMPACT_DEL && *nullify_node_flag_ptr == iter)
                                        continue;
                                for (bit_i = 0; bit_i < JA_BITS_PER_BYTE; bit_i++) {
                                        if (v & (1U << bit_i))
                                                nr_one[bit_i]++;
                                }
                                distrib_nr_child++;
                        }
                }
                break;
        }
        case RCU_JA_PIGEON:
        {
                unsigned int i;

                assert(mode == JA_RECOMPACT_DEL);
                for (i = 0; i < JA_ENTRY_PER_NODE; i++) {
                        struct cds_ja_inode_flag *iter;

                        iter = ja_pigeon_node_get_ith_pos(type, node, i);
                        if (!iter)
                                continue;
                        if (mode == JA_RECOMPACT_DEL && *nullify_node_flag_ptr == iter)
                                continue;
                        for (bit_i = 0; bit_i < JA_BITS_PER_BYTE; bit_i++) {
                                if (i & (1U << bit_i))
                                        nr_one[bit_i]++;
                        }
                        distrib_nr_child++;
                }
                break;
        }
        case RCU_JA_NULL:
                assert(mode == JA_RECOMPACT_ADD_NEXT);
                break;
        default:
                assert(0);
                break;
        }

        if (mode == JA_RECOMPACT_ADD_NEXT || mode == JA_RECOMPACT_ADD_SAME) {
                for (bit_i = 0; bit_i < JA_BITS_PER_BYTE; bit_i++) {
                        if (n & (1U << bit_i))
                                nr_one[bit_i]++;
                }
                distrib_nr_child++;
        }

        /*
         * The best bit selector is that for which the number of ones is
         * closest to half of the number of children in the
         * distribution. We calculate the distance using the double of
         * the sub-distribution sizes to eliminate truncation error.
         */
        for (bit_i = 0; bit_i < JA_BITS_PER_BYTE; bit_i++) {
                unsigned int distance_to_best;

                distance_to_best = abs_int((nr_one[bit_i] << 1U) - distrib_nr_child);
                if (distance_to_best < overall_best_distance) {
                        overall_best_distance = distance_to_best;
                        bitsel = bit_i;
                }
        }
        dbg_printf("1 dimension pool bit selection: (%u)\n", bitsel);
        return bitsel;
}

/*
 * Calculate bit distribution in two dimensions. Returns the two bits
 * (each 0 to 7) that splits the distribution in four sub-distributions
 * containing as much elements one compared to the other.
 */
static
void ja_node_sum_distribution_2d(enum ja_recompact mode,
                struct cds_ja *ja,
                unsigned int type_index,
                const struct cds_ja_type *type,
                struct cds_ja_inode *node,
                struct cds_ja_shadow_node *shadow_node,
                uint8_t n,
                struct cds_ja_inode_flag *child_node_flag,
                struct cds_ja_inode_flag **nullify_node_flag_ptr,
                unsigned int *_bitsel)
{
        uint8_t nr_2d_11[JA_BITS_PER_BYTE][JA_BITS_PER_BYTE],
                nr_2d_10[JA_BITS_PER_BYTE][JA_BITS_PER_BYTE],
                nr_2d_01[JA_BITS_PER_BYTE][JA_BITS_PER_BYTE],
                nr_2d_00[JA_BITS_PER_BYTE][JA_BITS_PER_BYTE];
        unsigned int bitsel[2] = { 0, 1 };
        unsigned int bit_i, bit_j;
        int overall_best_distance = INT_MAX;
        unsigned int distrib_nr_child = 0;

        memset(nr_2d_11, 0, sizeof(nr_2d_11));
        memset(nr_2d_10, 0, sizeof(nr_2d_10));
        memset(nr_2d_01, 0, sizeof(nr_2d_01));
        memset(nr_2d_00, 0, sizeof(nr_2d_00));

        switch (type->type_class) {
        case RCU_JA_LINEAR:
        {
                uint8_t nr_child =
                        ja_linear_node_get_nr_child(type, node);
                unsigned int i;

                for (i = 0; i < nr_child; i++) {
                        struct cds_ja_inode_flag *iter;
                        uint8_t v;

                        ja_linear_node_get_ith_pos(type, node, i, &v, &iter);
                        if (!iter)
                                continue;
                        if (mode == JA_RECOMPACT_DEL && *nullify_node_flag_ptr == iter)
                                continue;
                        for (bit_i = 0; bit_i < JA_BITS_PER_BYTE; bit_i++) {
                                for (bit_j = 0; bit_j < bit_i; bit_j++) {
                                        if ((v & (1U << bit_i)) && (v & (1U << bit_j))) {
                                                nr_2d_11[bit_i][bit_j]++;
                                        }
                                        if ((v & (1U << bit_i)) && !(v & (1U << bit_j))) {
                                                nr_2d_10[bit_i][bit_j]++;
                                        }
                                        if (!(v & (1U << bit_i)) && (v & (1U << bit_j))) {
                                                nr_2d_01[bit_i][bit_j]++;
                                        }
                                        if (!(v & (1U << bit_i)) && !(v & (1U << bit_j))) {
                                                nr_2d_00[bit_i][bit_j]++;
                                        }
                                }
                        }
                        distrib_nr_child++;
                }
                break;
        }
        case RCU_JA_POOL:
        {
                unsigned int pool_nr;

                for (pool_nr = 0; pool_nr < (1U << type->nr_pool_order); pool_nr++) {
                        struct cds_ja_inode *pool =
                                ja_pool_node_get_ith_pool(type,
                                        node, pool_nr);
                        uint8_t nr_child =
                                ja_linear_node_get_nr_child(type, pool);
                        unsigned int j;

                        for (j = 0; j < nr_child; j++) {
                                struct cds_ja_inode_flag *iter;
                                uint8_t v;

                                ja_linear_node_get_ith_pos(type, pool,
                                                j, &v, &iter);
                                if (!iter)
                                        continue;
                                if (mode == JA_RECOMPACT_DEL && *nullify_node_flag_ptr == iter)
                                        continue;
                                for (bit_i = 0; bit_i < JA_BITS_PER_BYTE; bit_i++) {
                                        for (bit_j = 0; bit_j < bit_i; bit_j++) {
                                                if ((v & (1U << bit_i)) && (v & (1U << bit_j))) {
                                                        nr_2d_11[bit_i][bit_j]++;
                                                }
                                                if ((v & (1U << bit_i)) && !(v & (1U << bit_j))) {
                                                        nr_2d_10[bit_i][bit_j]++;
                                                }
                                                if (!(v & (1U << bit_i)) && (v & (1U << bit_j))) {
                                                        nr_2d_01[bit_i][bit_j]++;
                                                }
                                                if (!(v & (1U << bit_i)) && !(v & (1U << bit_j))) {
                                                        nr_2d_00[bit_i][bit_j]++;
                                                }
                                        }
                                }
                                distrib_nr_child++;
                        }
                }
                break;
        }
        case RCU_JA_PIGEON:
        {
                unsigned int i;

                assert(mode == JA_RECOMPACT_DEL);
                for (i = 0; i < JA_ENTRY_PER_NODE; i++) {
                        struct cds_ja_inode_flag *iter;

                        iter = ja_pigeon_node_get_ith_pos(type, node, i);
                        if (!iter)
                                continue;
                        if (mode == JA_RECOMPACT_DEL && *nullify_node_flag_ptr == iter)
                                continue;
                        for (bit_i = 0; bit_i < JA_BITS_PER_BYTE; bit_i++) {
                                for (bit_j = 0; bit_j < bit_i; bit_j++) {
                                        if ((i & (1U << bit_i)) && (i & (1U << bit_j))) {
                                                nr_2d_11[bit_i][bit_j]++;
                                        }
                                        if ((i & (1U << bit_i)) && !(i & (1U << bit_j))) {
                                                nr_2d_10[bit_i][bit_j]++;
                                        }
                                        if (!(i & (1U << bit_i)) && (i & (1U << bit_j))) {
                                                nr_2d_01[bit_i][bit_j]++;
                                        }
                                        if (!(i & (1U << bit_i)) && !(i & (1U << bit_j))) {
                                                nr_2d_00[bit_i][bit_j]++;
                                        }
                                }
                        }
                        distrib_nr_child++;
                }
                break;
        }
        case RCU_JA_NULL:
                assert(mode == JA_RECOMPACT_ADD_NEXT);
                break;
        default:
                assert(0);
                break;
        }

        if (mode == JA_RECOMPACT_ADD_NEXT || mode == JA_RECOMPACT_ADD_SAME) {
                for (bit_i = 0; bit_i < JA_BITS_PER_BYTE; bit_i++) {
                        for (bit_j = 0; bit_j < bit_i; bit_j++) {
                                if ((n & (1U << bit_i)) && (n & (1U << bit_j))) {
                                        nr_2d_11[bit_i][bit_j]++;
                                }
                                if ((n & (1U << bit_i)) && !(n & (1U << bit_j))) {
                                        nr_2d_10[bit_i][bit_j]++;
                                }
                                if (!(n & (1U << bit_i)) && (n & (1U << bit_j))) {
                                        nr_2d_01[bit_i][bit_j]++;
                                }
                                if (!(n & (1U << bit_i)) && !(n & (1U << bit_j))) {
                                        nr_2d_00[bit_i][bit_j]++;
                                }
                        }
                }
                distrib_nr_child++;
        }

        /*
         * The best bit selector is that for which the number of nodes
         * in each sub-class is closest to one-fourth of the number of
         * children in the distribution. We calculate the distance using
         * 4 times the size of the sub-distribution to eliminate
         * truncation error.
         */
        for (bit_i = 0; bit_i < JA_BITS_PER_BYTE; bit_i++) {
                for (bit_j = 0; bit_j < bit_i; bit_j++) {
                        int distance_to_best[4];

                        distance_to_best[0] = (nr_2d_11[bit_i][bit_j] << 2U) - distrib_nr_child;
                        distance_to_best[1] = (nr_2d_10[bit_i][bit_j] << 2U) - distrib_nr_child;
                        distance_to_best[2] = (nr_2d_01[bit_i][bit_j] << 2U) - distrib_nr_child;
                        distance_to_best[3] = (nr_2d_00[bit_i][bit_j] << 2U) - distrib_nr_child;

                        /* Consider worse distance above best */
                        if (distance_to_best[1] > 0 && distance_to_best[1] > distance_to_best[0])
                                distance_to_best[0] = distance_to_best[1];
                        if (distance_to_best[2] > 0 && distance_to_best[2] > distance_to_best[0])
                                distance_to_best[0] = distance_to_best[2];
                        if (distance_to_best[3] > 0 && distance_to_best[3] > distance_to_best[0])
                                distance_to_best[0] = distance_to_best[3];

                        /*
                         * If our worse distance is better than overall,
                         * we become new best candidate.
                         */
                        if (distance_to_best[0] < overall_best_distance) {
                                overall_best_distance = distance_to_best[0];
                                bitsel[0] = bit_i;
                                bitsel[1] = bit_j;
                        }
                }
        }

        dbg_printf("2 dimensions pool bit selection: (%u,%u)\n", bitsel[0], bitsel[1]);

        /* Return our bit selection */
        _bitsel[0] = bitsel[0];
        _bitsel[1] = bitsel[1];
}

static
unsigned int find_nearest_type_index(unsigned int type_index,
                unsigned int nr_nodes)
{
        const struct cds_ja_type *type;

        assert(type_index != NODE_INDEX_NULL);
        if (nr_nodes == 0)
                return NODE_INDEX_NULL;
        for (;;) {
                type = &ja_types[type_index];
                if (nr_nodes < type->min_child)
                        type_index--;
                else if (nr_nodes > type->max_child)
                        type_index++;
                else
                        break;
        }
        return type_index;
}

/*
 * ja_node_recompact_add: recompact a node, adding a new child.
 * Return 0 on success, -EAGAIN if need to retry, or other negative
 * error value otherwise.
 */
static
int ja_node_recompact(enum ja_recompact mode,
                struct cds_ja *ja,
                unsigned int old_type_index,
                const struct cds_ja_type *old_type,
                struct cds_ja_inode *old_node,
                struct cds_ja_shadow_node *shadow_node,
                struct cds_ja_inode_flag **old_node_flag_ptr, uint8_t n,
                struct cds_ja_inode_flag *child_node_flag,
                struct cds_ja_inode_flag **nullify_node_flag_ptr,
                int level)
{
        unsigned int new_type_index;
        struct cds_ja_inode *new_node;
        struct cds_ja_shadow_node *new_shadow_node = NULL;
        const struct cds_ja_type *new_type;
        struct cds_ja_inode_flag *new_node_flag, *old_node_flag;
        int ret;
        int fallback = 0;

        old_node_flag = *old_node_flag_ptr;

        /*
         * Need to find nearest type index even for ADD_SAME, because
         * this recompaction, when applied to linear nodes, will garbage
         * collect dummy (NULL) entries, and can therefore cause a few
         * linear representations to be skipped.
         */
        switch (mode) {
        case JA_RECOMPACT_ADD_SAME:
                new_type_index = find_nearest_type_index(old_type_index,
                        shadow_node->nr_child + 1);
                dbg_printf("Recompact for node with %u children\n",
                        shadow_node->nr_child + 1);
                break;
        case JA_RECOMPACT_ADD_NEXT:
                if (!shadow_node || old_type_index == NODE_INDEX_NULL) {
                        new_type_index = 0;
                        dbg_printf("Recompact for NULL\n");
                } else {
                        new_type_index = find_nearest_type_index(old_type_index,
                                shadow_node->nr_child + 1);
                        dbg_printf("Recompact for node with %u children\n",
                                shadow_node->nr_child + 1);
                }
                break;
        case JA_RECOMPACT_DEL:
                new_type_index = find_nearest_type_index(old_type_index,
                        shadow_node->nr_child - 1);
                dbg_printf("Recompact for node with %u children\n",
                        shadow_node->nr_child - 1);
                break;
        default:
                assert(0);
        }

retry:          /* for fallback */
        dbg_printf("Recompact from type %d to type %d\n",
                        old_type_index, new_type_index);
        new_type = &ja_types[new_type_index];
        if (new_type_index != NODE_INDEX_NULL) {
                new_node = alloc_cds_ja_node(ja, new_type);
                if (!new_node)
                        return -ENOMEM;

                if (new_type->type_class == RCU_JA_POOL) {
                        switch (new_type->nr_pool_order) {
                        case 1:
                        {
                                unsigned int node_distrib_bitsel;

                                node_distrib_bitsel =
                                        ja_node_sum_distribution_1d(mode, ja,
                                                old_type_index, old_type,
                                                old_node, shadow_node,
                                                n, child_node_flag,
                                                nullify_node_flag_ptr);
                                assert(!((unsigned long) new_node & JA_POOL_1D_MASK));
                                new_node_flag = ja_node_flag_pool_1d(new_node,
                                        new_type_index, node_distrib_bitsel);
                                break;
                        }
                        case 2:
                        {
                                unsigned int node_distrib_bitsel[2];

                                ja_node_sum_distribution_2d(mode, ja,
                                        old_type_index, old_type,
                                        old_node, shadow_node,
                                        n, child_node_flag,
                                        nullify_node_flag_ptr,
                                        node_distrib_bitsel);
                                assert(!((unsigned long) new_node & JA_POOL_1D_MASK));
                                assert(!((unsigned long) new_node & JA_POOL_2D_MASK));
                                new_node_flag = ja_node_flag_pool_2d(new_node,
                                        new_type_index, node_distrib_bitsel);
                                break;
                        }
                        default:
                                assert(0);
                        }
                } else {
                        new_node_flag = ja_node_flag(new_node, new_type_index);
                }

                dbg_printf("Recompact inherit lock from %p\n", shadow_node);
                new_shadow_node = rcuja_shadow_set(ja->ht, new_node_flag, shadow_node, ja, level);
                if (!new_shadow_node) {
                        free_cds_ja_node(ja, new_node);
                        return -ENOMEM;
                }
                if (fallback)
                        new_shadow_node->fallback_removal_count =
                                                JA_FALLBACK_REMOVAL_COUNT;
        } else {
                new_node = NULL;
                new_node_flag = NULL;
        }

        assert(mode != JA_RECOMPACT_ADD_NEXT || old_type->type_class != RCU_JA_PIGEON);

        if (new_type_index == NODE_INDEX_NULL)
                goto skip_copy;

        switch (old_type->type_class) {
        case RCU_JA_LINEAR:
        {
                uint8_t nr_child =
                        ja_linear_node_get_nr_child(old_type, old_node);
                unsigned int i;

                for (i = 0; i < nr_child; i++) {
                        struct cds_ja_inode_flag *iter;
                        uint8_t v;

                        ja_linear_node_get_ith_pos(old_type, old_node, i, &v, &iter);
                        if (!iter)
                                continue;
                        if (mode == JA_RECOMPACT_DEL && *nullify_node_flag_ptr == iter)
                                continue;
                        ret = _ja_node_set_nth(new_type, new_node, new_node_flag,
                                        new_shadow_node,
                                        v, iter);
                        if (new_type->type_class == RCU_JA_POOL && ret) {
                                goto fallback_toosmall;
                        }
                        assert(!ret);
                }
                break;
        }
        case RCU_JA_POOL:
        {
                unsigned int pool_nr;

                for (pool_nr = 0; pool_nr < (1U << old_type->nr_pool_order); pool_nr++) {
                        struct cds_ja_inode *pool =
                                ja_pool_node_get_ith_pool(old_type,
                                        old_node, pool_nr);
                        uint8_t nr_child =
                                ja_linear_node_get_nr_child(old_type, pool);
                        unsigned int j;

                        for (j = 0; j < nr_child; j++) {
                                struct cds_ja_inode_flag *iter;
                                uint8_t v;

                                ja_linear_node_get_ith_pos(old_type, pool,
                                                j, &v, &iter);
                                if (!iter)
                                        continue;
                                if (mode == JA_RECOMPACT_DEL && *nullify_node_flag_ptr == iter)
                                        continue;
                                ret = _ja_node_set_nth(new_type, new_node, new_node_flag,
                                                new_shadow_node,
                                                v, iter);
                                if (new_type->type_class == RCU_JA_POOL
                                                && ret) {
                                        goto fallback_toosmall;
                                }
                                assert(!ret);
                        }
                }
                break;
        }
        case RCU_JA_NULL:
                assert(mode == JA_RECOMPACT_ADD_NEXT);
                break;
        case RCU_JA_PIGEON:
        {
                unsigned int i;

                assert(mode == JA_RECOMPACT_DEL);
                for (i = 0; i < JA_ENTRY_PER_NODE; i++) {
                        struct cds_ja_inode_flag *iter;

                        iter = ja_pigeon_node_get_ith_pos(old_type, old_node, i);
                        if (!iter)
                                continue;
                        if (mode == JA_RECOMPACT_DEL && *nullify_node_flag_ptr == iter)
                                continue;
                        ret = _ja_node_set_nth(new_type, new_node, new_node_flag,
                                        new_shadow_node,
                                        i, iter);
                        if (new_type->type_class == RCU_JA_POOL && ret) {
                                goto fallback_toosmall;
                        }
                        assert(!ret);
                }
                break;
        }
        default:
                assert(0);
                ret = -EINVAL;
                goto end;
        }
skip_copy:

        if (mode == JA_RECOMPACT_ADD_NEXT || mode == JA_RECOMPACT_ADD_SAME) {
                /* add node */
                ret = _ja_node_set_nth(new_type, new_node, new_node_flag,
                                new_shadow_node,
                                n, child_node_flag);
                if (new_type->type_class == RCU_JA_POOL && ret) {
                        goto fallback_toosmall;
                }
                assert(!ret);
        }

        if (fallback) {
                dbg_printf("Using fallback for %u children, node type index: %u, mode %s\n",
                        new_shadow_node->nr_child, old_type_index, mode == JA_RECOMPACT_ADD_NEXT ? "add_next" :
                                (mode == JA_RECOMPACT_DEL ? "del" : "add_same"));
                uatomic_inc(&ja->node_fallback_count_distribution[new_shadow_node->nr_child]);
        }

        /* Return pointer to new recompacted node through old_node_flag_ptr */
        *old_node_flag_ptr = new_node_flag;
        if (old_node) {
                int flags;

                flags = RCUJA_SHADOW_CLEAR_FREE_NODE;
                /*
                 * It is OK to free the lock associated with a node
                 * going to NULL, since we are holding the parent lock.
                 * This synchronizes removal with re-add of that node.
                 */
                if (new_type_index == NODE_INDEX_NULL)
                        flags |= RCUJA_SHADOW_CLEAR_FREE_LOCK;
                ret = rcuja_shadow_clear(ja->ht, old_node_flag, shadow_node,
                                flags);
                assert(!ret);
        }

        ret = 0;
end:
        return ret;

fallback_toosmall:
        /* fallback if next pool is too small */
        assert(new_shadow_node);
        ret = rcuja_shadow_clear(ja->ht, new_node_flag, new_shadow_node,
                        RCUJA_SHADOW_CLEAR_FREE_NODE);
        assert(!ret);

        switch (mode) {
        case JA_RECOMPACT_ADD_SAME:
                /*
                 * JA_RECOMPACT_ADD_SAME is only triggered if a linear
                 * node within a pool has unused entries. It should
                 * therefore _never_ be too small.
                 */
                assert(0);

                /* Fall-through */
        case JA_RECOMPACT_ADD_NEXT:
        {
                const struct cds_ja_type *next_type;

                /*
                 * Recompaction attempt on add failed. Should only
                 * happen if target node type is pool. Caused by
                 * hard-to-split distribution. Recompact using the next
                 * distribution size.
                 */
                assert(new_type->type_class == RCU_JA_POOL);
                next_type = &ja_types[new_type_index + 1];
                /*
                 * Try going to the next pool size if our population
                 * fits within its range. This is not flagged as a
                 * fallback.
                 */
                if (shadow_node->nr_child + 1 >= next_type->min_child
                                && shadow_node->nr_child + 1 <= next_type->max_child) {
                        new_type_index++;
                        goto retry;
                } else {
                        new_type_index++;
                        dbg_printf("Add fallback to type %d\n", new_type_index);
                        uatomic_inc(&ja->nr_fallback);
                        fallback = 1;
                        goto retry;
                }
                break;
        }
        case JA_RECOMPACT_DEL:
                /*
                 * Recompaction attempt on delete failed. Should only
                 * happen if target node type is pool. This is caused by
                 * a hard-to-split distribution. Recompact on same node
                 * size, but flag current node as "fallback" to ensure
                 * we don't attempt recompaction before some activity
                 * has reshuffled our node.
                 */
                assert(new_type->type_class == RCU_JA_POOL);
                new_type_index = old_type_index;
                dbg_printf("Delete fallback keeping type %d\n", new_type_index);
                uatomic_inc(&ja->nr_fallback);
                fallback = 1;
                goto retry;
        default:
                assert(0);
                return -EINVAL;
        }

        /*
         * Last resort fallback: pigeon.
         */
        new_type_index = (1UL << JA_TYPE_BITS) - 1;
        dbg_printf("Fallback to type %d\n", new_type_index);
        uatomic_inc(&ja->nr_fallback);
        fallback = 1;
        goto retry;
}

/*
 * Return 0 on success, -EAGAIN if need to retry, or other negative
 * error value otherwise.
 */
static
int ja_node_set_nth(struct cds_ja *ja,
                struct cds_ja_inode_flag **node_flag, uint8_t n,
                struct cds_ja_inode_flag *child_node_flag,
                struct cds_ja_shadow_node *shadow_node,
                int level)
{
        int ret;
        unsigned int type_index;
        const struct cds_ja_type *type;
        struct cds_ja_inode *node;

        dbg_printf("ja_node_set_nth for n=%u, node %p, shadow %p\n",
                (unsigned int) n, ja_node_ptr(*node_flag), shadow_node);

        node = ja_node_ptr(*node_flag);
        type_index = ja_node_type(*node_flag);
        type = &ja_types[type_index];
        ret = _ja_node_set_nth(type, node, *node_flag, shadow_node,
                        n, child_node_flag);
        switch (ret) {
        case -ENOSPC:
                /* Not enough space in node, need to recompact to next type. */
                ret = ja_node_recompact(JA_RECOMPACT_ADD_NEXT, ja, type_index, type, node,
                                shadow_node, node_flag, n, child_node_flag, NULL, level);
                break;
        case -ERANGE:
                /* Node needs to be recompacted. */
                ret = ja_node_recompact(JA_RECOMPACT_ADD_SAME, ja, type_index, type, node,
                                shadow_node, node_flag, n, child_node_flag, NULL, level);
                break;
        }
        return ret;
}

/*
 * Return 0 on success, -EAGAIN if need to retry, or other negative
 * error value otherwise.
 */
static
int ja_node_clear_ptr(struct cds_ja *ja,
                struct cds_ja_inode_flag **node_flag_ptr,       /* Pointer to location to nullify */
                struct cds_ja_inode_flag **parent_node_flag_ptr,        /* Address of parent ptr in its parent */
                struct cds_ja_shadow_node *shadow_node,         /* of parent */
                uint8_t n, int level)
{
        int ret;
        unsigned int type_index;
        const struct cds_ja_type *type;
        struct cds_ja_inode *node;

        dbg_printf("ja_node_clear_ptr for node %p, shadow %p, target ptr %p\n",
                ja_node_ptr(*parent_node_flag_ptr), shadow_node, node_flag_ptr);

        node = ja_node_ptr(*parent_node_flag_ptr);
        type_index = ja_node_type(*parent_node_flag_ptr);
        type = &ja_types[type_index];
        ret = _ja_node_clear_ptr(type, node, *parent_node_flag_ptr, shadow_node, node_flag_ptr, n);
        if (ret == -EFBIG) {
                /* Should try recompaction. */
                ret = ja_node_recompact(JA_RECOMPACT_DEL, ja, type_index, type, node,
                                shadow_node, parent_node_flag_ptr, n, NULL,
                                node_flag_ptr, level);
        }
        return ret;
}

struct cds_hlist_head cds_ja_lookup(struct cds_ja *ja, uint64_t key)
{
        unsigned int tree_depth, i;
        struct cds_ja_inode_flag *node_flag;
        struct cds_hlist_head head = { NULL };

        if (caa_unlikely(key > ja->key_max))
                return head;
        tree_depth = ja->tree_depth;
        node_flag = rcu_dereference(ja->root);

        /* level 0: root node */
        if (!ja_node_ptr(node_flag))
                return head;

        for (i = 1; i < tree_depth; i++) {
                uint8_t iter_key;

                iter_key = (uint8_t) (key >> (JA_BITS_PER_BYTE * (tree_depth - i - 1)));
                node_flag = ja_node_get_nth(node_flag, NULL, iter_key);
                dbg_printf("cds_ja_lookup iter key lookup %u finds node_flag %p\n",
                                (unsigned int) iter_key, node_flag);
                if (!ja_node_ptr(node_flag))
                        return head;
        }

        /* Last level lookup succeded. We got an actual match. */
        head.next = (struct cds_hlist_node *) node_flag;
        return head;
}

/*
 * We reached an unpopulated node. Create it and the children we need,
 * and then attach the entire branch to the current node. This may
 * trigger recompaction of the current node.  Locks needed: node lock
 * (for add), and, possibly, parent node lock (to update pointer due to
 * node recompaction).
 *
 * First take node lock, check if recompaction is needed, then take
 * parent lock (if needed).  Then we can proceed to create the new
 * branch. Publish the new branch, and release locks.
 * TODO: we currently always take the parent lock even when not needed.
 */
static
int ja_attach_node(struct cds_ja *ja,
                struct cds_ja_inode_flag **attach_node_flag_ptr,
                struct cds_ja_inode_flag *attach_node_flag,
                struct cds_ja_inode_flag *parent_attach_node_flag,
                struct cds_ja_inode_flag **old_node_flag_ptr,
                struct cds_ja_inode_flag *old_node_flag,
                uint64_t key,
                unsigned int level,
                struct cds_ja_node *child_node)
{
        struct cds_ja_shadow_node *shadow_node = NULL,
                        *parent_shadow_node = NULL;
        struct cds_hlist_head head;
        struct cds_ja_inode_flag *iter_node_flag, *iter_dest_node_flag;
        int ret, i;
        struct cds_ja_inode_flag *created_nodes[JA_MAX_DEPTH];
        int nr_created_nodes = 0;

        dbg_printf("Attach node at level %u (old_node_flag %p, attach_node_flag_ptr %p attach_node_flag %p, parent_attach_node_flag %p)\n",
                level, old_node_flag, attach_node_flag_ptr, attach_node_flag, parent_attach_node_flag);

        assert(!old_node_flag);
        if (attach_node_flag) {
                shadow_node = rcuja_shadow_lookup_lock(ja->ht, attach_node_flag);
                if (!shadow_node) {
                        ret = -EAGAIN;
                        goto end;
                }
        }
        if (parent_attach_node_flag) {
                parent_shadow_node = rcuja_shadow_lookup_lock(ja->ht,
                                                parent_attach_node_flag);
                if (!parent_shadow_node) {
                        ret = -EAGAIN;
                        goto unlock_shadow;
                }
        }

        if (old_node_flag_ptr && ja_node_ptr(*old_node_flag_ptr)) {
                /*
                 * Target node has been updated between RCU lookup and
                 * lock acquisition. We need to re-try lookup and
                 * attach.
                 */
                ret = -EAGAIN;
                goto unlock_parent;
        }

        /*
         * Perform a lookup query to handle the case where
         * old_node_flag_ptr is NULL. We cannot use it to check if the
         * node has been populated between RCU lookup and mutex
         * acquisition.
         */
        if (!old_node_flag_ptr) {
                uint8_t iter_key;
                struct cds_ja_inode_flag *lookup_node_flag;
                struct cds_ja_inode_flag **lookup_node_flag_ptr;

                iter_key = (uint8_t) (key >> (JA_BITS_PER_BYTE * (ja->tree_depth - level)));
                lookup_node_flag = ja_node_get_nth(attach_node_flag,
                        &lookup_node_flag_ptr,
                        iter_key);
                if (lookup_node_flag) {
                        ret = -EEXIST;
                        goto unlock_parent;
                }
        }

        if (attach_node_flag_ptr && ja_node_ptr(*attach_node_flag_ptr) !=
                        ja_node_ptr(attach_node_flag)) {
                /*
                 * Target node has been updated between RCU lookup and
                 * lock acquisition. We need to re-try lookup and
                 * attach.
                 */
                ret = -EAGAIN;
                goto unlock_parent;
        }

        /* Create new branch, starting from bottom */
        CDS_INIT_HLIST_HEAD(&head);
        cds_hlist_add_head_rcu(&child_node->list, &head);
        iter_node_flag = (struct cds_ja_inode_flag *) head.next;

        for (i = ja->tree_depth - 1; i >= (int) level; i--) {
                uint8_t iter_key;

                iter_key = (uint8_t) (key >> (JA_BITS_PER_BYTE * (ja->tree_depth - i - 1)));
                dbg_printf("branch creation level %d, key %u\n",
                                i, (unsigned int) iter_key);
                iter_dest_node_flag = NULL;
                ret = ja_node_set_nth(ja, &iter_dest_node_flag,
                        iter_key,
                        iter_node_flag,
                        NULL, i);
                if (ret) {
                        dbg_printf("branch creation error %d\n", ret);
                        goto check_error;
                }
                created_nodes[nr_created_nodes++] = iter_dest_node_flag;
                iter_node_flag = iter_dest_node_flag;
        }
        assert(level > 0);

        /* Publish branch */
        if (level == 1) {
                /*
                 * Attaching to root node.
                 */
                rcu_assign_pointer(ja->root, iter_node_flag);
        } else {
                uint8_t iter_key;

                iter_key = (uint8_t) (key >> (JA_BITS_PER_BYTE * (ja->tree_depth - level)));
                dbg_printf("publish branch at level %d, key %u\n",
                                level - 1, (unsigned int) iter_key);
                /* We need to use set_nth on the previous level. */
                iter_dest_node_flag = attach_node_flag;
                ret = ja_node_set_nth(ja, &iter_dest_node_flag,
                        iter_key,
                        iter_node_flag,
                        shadow_node, level - 1);
                if (ret) {
                        dbg_printf("branch publish error %d\n", ret);
                        goto check_error;
                }
                /*
                 * Attach branch
                 */
                rcu_assign_pointer(*attach_node_flag_ptr, iter_dest_node_flag);
        }

        /* Success */
        ret = 0;

check_error:
        if (ret) {
                for (i = 0; i < nr_created_nodes; i++) {
                        int tmpret;
                        int flags;

                        flags = RCUJA_SHADOW_CLEAR_FREE_LOCK;
                        if (i)
                                flags |= RCUJA_SHADOW_CLEAR_FREE_NODE;
                        tmpret = rcuja_shadow_clear(ja->ht,
                                        created_nodes[i],
                                        NULL,
                                        flags);
                        assert(!tmpret);
                }
        }
unlock_parent:
        if (parent_shadow_node)
                rcuja_shadow_unlock(parent_shadow_node);
unlock_shadow:
        if (shadow_node)
                rcuja_shadow_unlock(shadow_node);
end:
        return ret;
}

/*
 * Lock the parent containing the hlist head pointer, and add node to list of
 * duplicates. Failure can happen if concurrent update changes the
 * parent before we get the lock. We return -EAGAIN in that case.
 * Return 0 on success, negative error value on failure.
 */
static
int ja_chain_node(struct cds_ja *ja,
                struct cds_ja_inode_flag *parent_node_flag,
                struct cds_ja_inode_flag **node_flag_ptr,
                struct cds_ja_inode_flag *node_flag,
                struct cds_ja_node *node)
{
        struct cds_ja_shadow_node *shadow_node;
        int ret = 0;

        shadow_node = rcuja_shadow_lookup_lock(ja->ht, parent_node_flag);
        if (!shadow_node) {
                return -EAGAIN;
        }
        if (ja_node_ptr(*node_flag_ptr) != ja_node_ptr(node_flag)) {
                ret = -EAGAIN;
                goto end;
        }
        cds_hlist_add_head_rcu(&node->list, (struct cds_hlist_head *) node_flag_ptr);
end:
        rcuja_shadow_unlock(shadow_node);
        return ret;
}

static
int _cds_ja_add(struct cds_ja *ja, uint64_t key,
                struct cds_ja_node *new_node,
                struct cds_ja_node **unique_node_ret)
{
        unsigned int tree_depth, i;
        struct cds_ja_inode_flag *attach_node_flag,
                *parent_node_flag,
                *parent2_node_flag,
                *node_flag,
                *parent_attach_node_flag;
        struct cds_ja_inode_flag **attach_node_flag_ptr,
                **parent_node_flag_ptr,
                **node_flag_ptr;
        int ret;

        if (caa_unlikely(key > ja->key_max)) {
                return -EINVAL;
        }
        tree_depth = ja->tree_depth;

retry:
        dbg_printf("cds_ja_add attempt: key %" PRIu64 ", node %p\n",
                key, new_node);
        parent2_node_flag = NULL;
        parent_node_flag =
                (struct cds_ja_inode_flag *) &ja->root; /* Use root ptr address as key for mutex */
        parent_node_flag_ptr = NULL;
        node_flag = rcu_dereference(ja->root);
        node_flag_ptr = &ja->root;

        /* Iterate on all internal levels */
        for (i = 1; i < tree_depth; i++) {
                uint8_t iter_key;

                if (!ja_node_ptr(node_flag))
                        break;
                dbg_printf("cds_ja_add iter parent2_node_flag %p parent_node_flag %p node_flag_ptr %p node_flag %p\n",
                                parent2_node_flag, parent_node_flag, node_flag_ptr, node_flag);
                iter_key = (uint8_t) (key >> (JA_BITS_PER_BYTE * (tree_depth - i - 1)));
                parent2_node_flag = parent_node_flag;
                parent_node_flag = node_flag;
                parent_node_flag_ptr = node_flag_ptr;
                node_flag = ja_node_get_nth(node_flag,
                        &node_flag_ptr,
                        iter_key);
        }

        /*
         * We reached either bottom of tree or internal NULL node,
         * simply add node to last internal level, or chain it if key is
         * already present.
         */
        if (!ja_node_ptr(node_flag)) {
                dbg_printf("cds_ja_add NULL parent2_node_flag %p parent_node_flag %p node_flag_ptr %p node_flag %p\n",
                                parent2_node_flag, parent_node_flag, node_flag_ptr, node_flag);

                attach_node_flag = parent_node_flag;
                attach_node_flag_ptr = parent_node_flag_ptr;
                parent_attach_node_flag = parent2_node_flag;

                ret = ja_attach_node(ja, attach_node_flag_ptr,
                                attach_node_flag,
                                parent_attach_node_flag,
                                node_flag_ptr,
                                node_flag,
                                key, i, new_node);
        } else {
                if (unique_node_ret) {
                        *unique_node_ret = (struct cds_ja_node *) ja_node_ptr(node_flag);
                        return -EEXIST;
                }

                dbg_printf("cds_ja_add duplicate parent2_node_flag %p parent_node_flag %p node_flag_ptr %p node_flag %p\n",
                                parent2_node_flag, parent_node_flag, node_flag_ptr, node_flag);

                attach_node_flag = node_flag;
                attach_node_flag_ptr = node_flag_ptr;
                parent_attach_node_flag = parent_node_flag;

                ret = ja_chain_node(ja,
                        parent_attach_node_flag,
                        attach_node_flag_ptr,
                        attach_node_flag,
                        new_node);
        }
        if (ret == -EAGAIN || ret == -EEXIST)
                goto retry;

        return ret;
}

int cds_ja_add(struct cds_ja *ja, uint64_t key,
                struct cds_ja_node *new_node)
{
        return _cds_ja_add(ja, key, new_node, NULL);
}

struct cds_ja_node *cds_ja_add_unique(struct cds_ja *ja, uint64_t key,
                struct cds_ja_node *new_node)
{
        int ret;
        struct cds_ja_node *ret_node;

        ret = _cds_ja_add(ja, key, new_node, &ret_node);
        if (ret == -EEXIST)
                return ret_node;
        else
                return new_node;
}

/*
 * Note: there is no need to lookup the pointer address associated with
 * each node's nth item after taking the lock: it's already been done by
 * cds_ja_del while holding the rcu read-side lock, and our node rules
 * ensure that when a match value -> pointer is found in a node, it is
 * _NEVER_ changed for that node without recompaction, and recompaction
 * reallocates the node.
 * However, when a child is removed from "linear" nodes, its pointer
 * is set to NULL. We therefore check, while holding the locks, if this
 * pointer is NULL, and return -ENOENT to the caller if it is the case.
 */
static
int ja_detach_node(struct cds_ja *ja,
                struct cds_ja_inode_flag **snapshot,
                struct cds_ja_inode_flag ***snapshot_ptr,
                uint8_t *snapshot_n,
                int nr_snapshot,
                uint64_t key,
                struct cds_ja_node *node)
{
        struct cds_ja_shadow_node *shadow_nodes[JA_MAX_DEPTH];
        struct cds_ja_inode_flag **node_flag_ptr = NULL,
                        *parent_node_flag = NULL,
                        **parent_node_flag_ptr = NULL;
        struct cds_ja_inode_flag *iter_node_flag;
        int ret, i, nr_shadow = 0, nr_clear = 0, nr_branch = 0;
        uint8_t n = 0;

        assert(nr_snapshot == ja->tree_depth + 1);

        /*
         * From the last internal level node going up, get the node
         * lock, check if the node has only one child left. If it is the
         * case, we continue iterating upward. When we reach a node
         * which has more that one child left, we lock the parent, and
         * proceed to the node deletion (removing its children too).
         */
        for (i = nr_snapshot - 2; i >= 1; i--) {
                struct cds_ja_shadow_node *shadow_node;

                shadow_node = rcuja_shadow_lookup_lock(ja->ht,
                                        snapshot[i]);
                if (!shadow_node) {
                        ret = -EAGAIN;
                        goto end;
                }
                shadow_nodes[nr_shadow++] = shadow_node;

                /*
                 * Check if node has been removed between RCU
                 * lookup and lock acquisition.
                 */
                assert(snapshot_ptr[i + 1]);
                if (ja_node_ptr(*snapshot_ptr[i + 1])
                                != ja_node_ptr(snapshot[i + 1])) {
                        ret = -ENOENT;
                        goto end;
                }

                assert(shadow_node->nr_child > 0);
                if (shadow_node->nr_child == 1 && i > 1)
                        nr_clear++;
                nr_branch++;
                if (shadow_node->nr_child > 1 || i == 1) {
                        /* Lock parent and break */
                        shadow_node = rcuja_shadow_lookup_lock(ja->ht,
                                        snapshot[i - 1]);
                        if (!shadow_node) {
                                ret = -EAGAIN;
                                goto end;
                        }
                        shadow_nodes[nr_shadow++] = shadow_node;

                        /*
                         * Check if node has been removed between RCU
                         * lookup and lock acquisition.
                         */
                        assert(snapshot_ptr[i]);
                        if (ja_node_ptr(*snapshot_ptr[i])
                                        != ja_node_ptr(snapshot[i])) {
                                ret = -ENOENT;
                                goto end;
                        }

                        node_flag_ptr = snapshot_ptr[i + 1];
                        n = snapshot_n[i + 1];
                        parent_node_flag_ptr = snapshot_ptr[i];
                        parent_node_flag = snapshot[i];

                        if (i > 1) {
                                /*
                                 * Lock parent's parent, in case we need
                                 * to recompact parent.
                                 */
                                shadow_node = rcuja_shadow_lookup_lock(ja->ht,
                                                snapshot[i - 2]);
                                if (!shadow_node) {
                                        ret = -EAGAIN;
                                        goto end;
                                }
                                shadow_nodes[nr_shadow++] = shadow_node;

                                /*
                                 * Check if node has been removed between RCU
                                 * lookup and lock acquisition.
                                 */
                                assert(snapshot_ptr[i - 1]);
                                if (ja_node_ptr(*snapshot_ptr[i - 1])
                                                != ja_node_ptr(snapshot[i - 1])) {
                                        ret = -ENOENT;
                                        goto end;
                                }
                        }

                        break;
                }
        }

        /*
         * At this point, we want to delete all nodes that are about to
         * be removed from shadow_nodes (except the last one, which is
         * either the root or the parent of the upmost node with 1
         * child). OK to free lock here, because RCU read lock is held,
         * and free only performed in call_rcu.
         */

        for (i = 0; i < nr_clear; i++) {
                ret = rcuja_shadow_clear(ja->ht,
                                shadow_nodes[i]->node_flag,
                                shadow_nodes[i],
                                RCUJA_SHADOW_CLEAR_FREE_NODE
                                | RCUJA_SHADOW_CLEAR_FREE_LOCK);
                assert(!ret);
        }

        iter_node_flag = parent_node_flag;
        /* Remove from parent */
        ret = ja_node_clear_ptr(ja,
                node_flag_ptr,          /* Pointer to location to nullify */
                &iter_node_flag,        /* Old new parent ptr in its parent */
                shadow_nodes[nr_branch - 1],    /* of parent */
                n, nr_branch - 1);
        if (ret)
                goto end;

        dbg_printf("ja_detach_node: publish %p instead of %p\n",
                iter_node_flag, *parent_node_flag_ptr);
        /* Update address of parent ptr in its parent */
        rcu_assign_pointer(*parent_node_flag_ptr, iter_node_flag);

end:
        for (i = 0; i < nr_shadow; i++)
                rcuja_shadow_unlock(shadow_nodes[i]);
        return ret;
}

static
int ja_unchain_node(struct cds_ja *ja,
                struct cds_ja_inode_flag *parent_node_flag,
                struct cds_ja_inode_flag **node_flag_ptr,
                struct cds_ja_inode_flag *node_flag,
                struct cds_ja_node *node)
{
        struct cds_ja_shadow_node *shadow_node;
        struct cds_hlist_node *hlist_node;
        struct cds_hlist_head hlist_head;
        int ret = 0, count = 0, found = 0;

        shadow_node = rcuja_shadow_lookup_lock(ja->ht, parent_node_flag);
        if (!shadow_node)
                return -EAGAIN;
        if (ja_node_ptr(*node_flag_ptr) != ja_node_ptr(node_flag)) {
                ret = -EAGAIN;
                goto end;
        }
        hlist_head.next = (struct cds_hlist_node *) ja_node_ptr(node_flag);
        /*
         * Retry if another thread removed all but one of duplicates
         * since check (this check was performed without lock).
         * Ensure that the node we are about to remove is still in the
         * list (while holding lock).
         */
        cds_hlist_for_each_rcu(hlist_node, &hlist_head) {
                if (count == 0) {
                        /* FIXME: currently a work-around */
                        hlist_node->prev = (struct cds_hlist_node *) node_flag_ptr;
                }
                count++;
                if (hlist_node == &node->list)
                        found++;
        }
        assert(found <= 1);
        if (!found || count == 1) {
                ret = -EAGAIN;
                goto end;
        }
        cds_hlist_del_rcu(&node->list);
        /*
         * Validate that we indeed removed the node from linked list.
         */
        assert(ja_node_ptr(*node_flag_ptr) != (struct cds_ja_inode *) node);
end:
        rcuja_shadow_unlock(shadow_node);
        return ret;
}

/*
 * Called with RCU read lock held.
 */
int cds_ja_del(struct cds_ja *ja, uint64_t key,
                struct cds_ja_node *node)
{
        unsigned int tree_depth, i;
        struct cds_ja_inode_flag *snapshot[JA_MAX_DEPTH];
        struct cds_ja_inode_flag **snapshot_ptr[JA_MAX_DEPTH];
        uint8_t snapshot_n[JA_MAX_DEPTH];
        struct cds_ja_inode_flag *node_flag;
        struct cds_ja_inode_flag **prev_node_flag_ptr,
                **node_flag_ptr;
        int nr_snapshot;
        int ret;

        if (caa_unlikely(key > ja->key_max))
                return -EINVAL;
        tree_depth = ja->tree_depth;

retry:
        nr_snapshot = 0;
        dbg_printf("cds_ja_del attempt: key %" PRIu64 ", node %p\n",
                key, node);

        /* snapshot for level 0 is only for shadow node lookup */
        snapshot_n[0] = 0;
        snapshot_n[1] = 0;
        snapshot_ptr[nr_snapshot] = NULL;
        snapshot[nr_snapshot++] = (struct cds_ja_inode_flag *) &ja->root;
        node_flag = rcu_dereference(ja->root);
        prev_node_flag_ptr = &ja->root;
        node_flag_ptr = &ja->root;

        /* Iterate on all internal levels */
        for (i = 1; i < tree_depth; i++) {
                uint8_t iter_key;

                dbg_printf("cds_ja_del iter node_flag %p\n",
                                node_flag);
                if (!ja_node_ptr(node_flag)) {
                        return -ENOENT;
                }
                iter_key = (uint8_t) (key >> (JA_BITS_PER_BYTE * (tree_depth - i - 1)));
                snapshot_n[nr_snapshot + 1] = iter_key;
                snapshot_ptr[nr_snapshot] = prev_node_flag_ptr;
                snapshot[nr_snapshot++] = node_flag;
                node_flag = ja_node_get_nth(node_flag,
                        &node_flag_ptr,
                        iter_key);
                if (node_flag)
                        prev_node_flag_ptr = node_flag_ptr;
                dbg_printf("cds_ja_del iter key lookup %u finds node_flag %p, prev_node_flag_ptr %p\n",
                                (unsigned int) iter_key, node_flag,
                                prev_node_flag_ptr);
        }
        /*
         * We reached bottom of tree, try to find the node we are trying
         * to remove. Fail if we cannot find it.
         */
        if (!ja_node_ptr(node_flag)) {
                dbg_printf("cds_ja_del: no node found for key %" PRIu64 "\n",
                                key);
                return -ENOENT;
        } else {
                struct cds_hlist_head hlist_head;
                struct cds_hlist_node *hlist_node;
                struct cds_ja_node *entry, *match = NULL;
                int count = 0;

                hlist_head.next =
                        (struct cds_hlist_node *) ja_node_ptr(node_flag);
                cds_hlist_for_each_entry_rcu(entry,
                                hlist_node,
                                &hlist_head,
                                list) {
                        dbg_printf("cds_ja_del: compare %p with entry %p\n", node, entry);
                        if (entry == node)
                                match = entry;
                        count++;
                }
                if (!match) {
                        dbg_printf("cds_ja_del: no node match for node %p key %" PRIu64 "\n", node, key);
                        return -ENOENT;
                }
                assert(count > 0);
                if (count == 1) {
                        /*
                         * Removing last of duplicates. Last snapshot
                         * does not have a shadow node (external leafs).
                         */
                        snapshot_ptr[nr_snapshot] = prev_node_flag_ptr;
                        snapshot[nr_snapshot++] = node_flag;
                        ret = ja_detach_node(ja, snapshot, snapshot_ptr,
                                        snapshot_n, nr_snapshot, key, node);
                } else {
                        ret = ja_unchain_node(ja, snapshot[nr_snapshot - 1],
                                node_flag_ptr, node_flag, match);
                }
        }
        /*
         * Explanation of -ENOENT handling: caused by concurrent delete
         * between RCU lookup and actual removal. Need to re-do the
         * lookup and removal attempt.
         */
        if (ret == -EAGAIN || ret == -ENOENT)
                goto retry;
        return ret;
}

struct cds_ja *_cds_ja_new(unsigned int key_bits,
                const struct rcu_flavor_struct *flavor)
{
        struct cds_ja *ja;
        int ret;
        struct cds_ja_shadow_node *root_shadow_node;

        ja = calloc(sizeof(*ja), 1);
        if (!ja)
                goto ja_error;

        switch (key_bits) {
        case 8:
        case 16:
        case 24:
        case 32:
        case 40:
        case 48:
        case 56:
                ja->key_max = (1ULL << key_bits) - 1;
                break;
        case 64:
                ja->key_max = UINT64_MAX;
                break;
        default:
                goto check_error;
        }

        /* ja->root is NULL */
        /* tree_depth 0 is for pointer to root node */
        ja->tree_depth = (key_bits >> JA_LOG2_BITS_PER_BYTE) + 1;
        assert(ja->tree_depth <= JA_MAX_DEPTH);
        ja->ht = rcuja_create_ht(flavor);
        if (!ja->ht)
                goto ht_error;

        /*
         * Note: we should not free this node until judy array destroy.
         */
        root_shadow_node = rcuja_shadow_set(ja->ht,
                        (struct cds_ja_inode_flag *) &ja->root,
                        NULL, ja, 0);
        if (!root_shadow_node) {
                ret = -ENOMEM;
                goto ht_node_error;
        }

        return ja;

ht_node_error:
        ret = rcuja_delete_ht(ja->ht);
        assert(!ret);
ht_error:
check_error:
        free(ja);
ja_error:
        return NULL;
}

/*
 * Called from RCU read-side CS.
 */
__attribute__((visibility("protected")))
void rcuja_free_all_children(struct cds_ja_shadow_node *shadow_node,
                struct cds_ja_inode_flag *node_flag,
                void (*free_node_cb)(struct rcu_head *head))
{
        const struct rcu_flavor_struct *flavor;
        unsigned int type_index;
        struct cds_ja_inode *node;
        const struct cds_ja_type *type;

        flavor = cds_lfht_rcu_flavor(shadow_node->ja->ht);
        node = ja_node_ptr(node_flag);
        assert(node != NULL);
        type_index = ja_node_type(node_flag);
        type = &ja_types[type_index];

        switch (type->type_class) {
        case RCU_JA_LINEAR:
        {
                uint8_t nr_child =
                        ja_linear_node_get_nr_child(type, node);
                unsigned int i;

                for (i = 0; i < nr_child; i++) {
                        struct cds_ja_inode_flag *iter;
                        struct cds_hlist_head head;
                        struct cds_ja_node *entry;
                        struct cds_hlist_node *pos, *tmp;
                        uint8_t v;

                        ja_linear_node_get_ith_pos(type, node, i, &v, &iter);
                        if (!iter)
                                continue;
                        head.next = (struct cds_hlist_node *) iter;
                        cds_hlist_for_each_entry_safe(entry, pos, tmp, &head, list) {
                                flavor->update_call_rcu(&entry->head, free_node_cb);
                        }
                }
                break;
        }
        case RCU_JA_POOL:
        {
                unsigned int pool_nr;

                for (pool_nr = 0; pool_nr < (1U << type->nr_pool_order); pool_nr++) {
                        struct cds_ja_inode *pool =
                                ja_pool_node_get_ith_pool(type, node, pool_nr);
                        uint8_t nr_child =
                                ja_linear_node_get_nr_child(type, pool);
                        unsigned int j;

                        for (j = 0; j < nr_child; j++) {
                                struct cds_ja_inode_flag *iter;
                                struct cds_hlist_head head;
                                struct cds_ja_node *entry;
                                struct cds_hlist_node *pos, *tmp;
                                uint8_t v;

                                ja_linear_node_get_ith_pos(type, pool, j, &v, &iter);
                                if (!iter)
                                        continue;
                                head.next = (struct cds_hlist_node *) iter;
                                cds_hlist_for_each_entry_safe(entry, pos, tmp, &head, list) {
                                        flavor->update_call_rcu(&entry->head, free_node_cb);
                                }
                        }
                }
                break;
        }
        case RCU_JA_NULL:
                break;
        case RCU_JA_PIGEON:
        {
                unsigned int i;

                for (i = 0; i < JA_ENTRY_PER_NODE; i++) {
                        struct cds_ja_inode_flag *iter;
                        struct cds_hlist_head head;
                        struct cds_ja_node *entry;
                        struct cds_hlist_node *pos, *tmp;

                        iter = ja_pigeon_node_get_ith_pos(type, node, i);
                        if (!iter)
                                continue;
                        head.next = (struct cds_hlist_node *) iter;
                        cds_hlist_for_each_entry_safe(entry, pos, tmp, &head, list) {
                                flavor->update_call_rcu(&entry->head, free_node_cb);
                        }
                }
                break;
        }
        default:
                assert(0);
        }
}

static
void print_debug_fallback_distribution(struct cds_ja *ja)
{
        int i;

        fprintf(stderr, "Fallback node distribution:\n");
        for (i = 0; i < JA_ENTRY_PER_NODE; i++) {
                if (!ja->node_fallback_count_distribution[i])
                        continue;
                fprintf(stderr, "       %3u: %4lu\n",
                        i, ja->node_fallback_count_distribution[i]);
        }
}

static
int ja_final_checks(struct cds_ja *ja)
{
        double fallback_ratio;
        unsigned long na, nf, nr_fallback;
        int ret = 0;

        fallback_ratio = (double) uatomic_read(&ja->nr_fallback);
        fallback_ratio /= (double) uatomic_read(&ja->nr_nodes_allocated);
        nr_fallback = uatomic_read(&ja->nr_fallback);
        if (nr_fallback)
                fprintf(stderr,
                        "[warning] RCU Judy Array used %lu fallback node(s) (ratio: %g)\n",
                        uatomic_read(&ja->nr_fallback),
                        fallback_ratio);

        na = uatomic_read(&ja->nr_nodes_allocated);
        nf = uatomic_read(&ja->nr_nodes_freed);
        dbg_printf("Nodes allocated: %lu, Nodes freed: %lu.\n", na, nf);
        if (nr_fallback)
                print_debug_fallback_distribution(ja);

        if (na != nf) {
                fprintf(stderr, "[error] Judy array leaked %ld nodes. Allocated: %lu, freed: %lu.\n",
                        (long) na - nf, na, nf);
                ret = -1;
        }
        return ret;
}

/*
 * There should be no more concurrent add to the judy array while it is
 * being destroyed (ensured by the caller).
 */
int cds_ja_destroy(struct cds_ja *ja,
                void (*free_node_cb)(struct rcu_head *head))
{
        const struct rcu_flavor_struct *flavor;
        int ret;

        flavor = cds_lfht_rcu_flavor(ja->ht);
        rcuja_shadow_prune(ja->ht,
                RCUJA_SHADOW_CLEAR_FREE_NODE | RCUJA_SHADOW_CLEAR_FREE_LOCK,
                free_node_cb);
        flavor->thread_offline();
        ret = rcuja_delete_ht(ja->ht);
        if (ret)
                return ret;

        /* Wait for in-flight call_rcu free to complete. */
        flavor->barrier();

        flavor->thread_online();
        ret = ja_final_checks(ja);
        free(ja);
        return ret;
}