Subversion Repositories or1k_soc_on_altera_embedded_dev_kit

/*

 * lib/prio_tree.c - priority search tree

 *

 * Copyright (C) 2004, Rajesh Venkatasubramanian <vrajesh@umich.edu>

 *

 * This file is released under the GPL v2.

 *

 * Based on the radix priority search tree proposed by Edward M. McCreight

 * SIAM Journal of Computing, vol. 14, no.2, pages 257-276, May 1985

 *

 * 02Feb2004    Initial version

 */

#include <linux/init.h>

#include <linux/mm.h>

#include <linux/prio_tree.h>

/*

 * A clever mix of heap and radix trees forms a radix priority search tree (PST)

 * which is useful for storing intervals, e.g, we can consider a vma as a closed

 * interval of file pages [offset_begin, offset_end], and store all vmas that

 * map a file in a PST. Then, using the PST, we can answer a stabbing query,

 * i.e., selecting a set of stored intervals (vmas) that overlap with (map) a

 * given input interval X (a set of consecutive file pages), in "O(log n + m)"

 * time where 'log n' is the height of the PST, and 'm' is the number of stored

 * intervals (vmas) that overlap (map) with the input interval X (the set of

 * consecutive file pages).

 *

 * In our implementation, we store closed intervals of the form [radix_index,

 * heap_index]. We assume that always radix_index <= heap_index. McCreight's PST

 * is designed for storing intervals with unique radix indices, i.e., each

 * interval have different radix_index. However, this limitation can be easily

 * overcome by using the size, i.e., heap_index - radix_index, as part of the

 * index, so we index the tree using [(radix_index,size), heap_index].

 *

 * When the above-mentioned indexing scheme is used, theoretically, in a 32 bit

 * machine, the maximum height of a PST can be 64. We can use a balanced version

 * of the priority search tree to optimize the tree height, but the balanced

 * tree proposed by McCreight is too complex and memory-hungry for our purpose.

 */

/*

 * The following macros are used for implementing prio_tree for i_mmap

 */

#define RADIX_INDEX(vma)  ((vma)->vm_pgoff)

#define VMA_SIZE(vma)     (((vma)->vm_end - (vma)->vm_start) >> PAGE_SHIFT)

/* avoid overflow */

#define HEAP_INDEX(vma)   ((vma)->vm_pgoff + (VMA_SIZE(vma) - 1))

static void get_index(const struct prio_tree_root *root,

    const struct prio_tree_node *node,

    unsigned long *radix, unsigned long *heap)

{

        if (root->raw) {

                struct vm_area_struct *vma = prio_tree_entry(

                    node, struct vm_area_struct, shared.prio_tree_node);

                *radix = RADIX_INDEX(vma);

                *heap = HEAP_INDEX(vma);

        }

        else {

                *radix = node->start;

                *heap = node->last;

        }

}

static unsigned long index_bits_to_maxindex[BITS_PER_LONG];

void __init prio_tree_init(void)

{

        unsigned int i;

        for (i = 0; i < ARRAY_SIZE(index_bits_to_maxindex) - 1; i++)

                index_bits_to_maxindex[i] = (1UL << (i + 1)) - 1;

        index_bits_to_maxindex[ARRAY_SIZE(index_bits_to_maxindex) - 1] = ~0UL;

}

/*

 * Maximum heap_index that can be stored in a PST with index_bits bits

 */

static inline unsigned long prio_tree_maxindex(unsigned int bits)

{

        return index_bits_to_maxindex[bits - 1];

}

/*

 * Extend a priority search tree so that it can store a node with heap_index

 * max_heap_index. In the worst case, this algorithm takes O((log n)^2).

 * However, this function is used rarely and the common case performance is

 * not bad.

 */

static struct prio_tree_node *prio_tree_expand(struct prio_tree_root *root,

                struct prio_tree_node *node, unsigned long max_heap_index)

{

        struct prio_tree_node *first = NULL, *prev, *last = NULL;

        if (max_heap_index > prio_tree_maxindex(root->index_bits))

                root->index_bits++;

        while (max_heap_index > prio_tree_maxindex(root->index_bits)) {

                root->index_bits++;

                if (prio_tree_empty(root))

                        continue;

                if (first == NULL) {

                        first = root->prio_tree_node;

                        prio_tree_remove(root, root->prio_tree_node);

                        INIT_PRIO_TREE_NODE(first);

                        last = first;

                } else {

                        prev = last;

                        last = root->prio_tree_node;

                        prio_tree_remove(root, root->prio_tree_node);

                        INIT_PRIO_TREE_NODE(last);

                        prev->left = last;

                        last->parent = prev;

                }

        }

        INIT_PRIO_TREE_NODE(node);

        if (first) {

                node->left = first;

                first->parent = node;

        } else

                last = node;

        if (!prio_tree_empty(root)) {

                last->left = root->prio_tree_node;

                last->left->parent = last;

        }

        root->prio_tree_node = node;

        return node;

}

/*

 * Replace a prio_tree_node with a new node and return the old node

 */

struct prio_tree_node *prio_tree_replace(struct prio_tree_root *root,

                struct prio_tree_node *old, struct prio_tree_node *node)

{

        INIT_PRIO_TREE_NODE(node);

        if (prio_tree_root(old)) {

                BUG_ON(root->prio_tree_node != old);

                /*

                 * We can reduce root->index_bits here. However, it is complex

                 * and does not help much to improve performance (IMO).

                 */

                node->parent = node;

                root->prio_tree_node = node;

        } else {

                node->parent = old->parent;

                if (old->parent->left == old)

                        old->parent->left = node;

                else

                        old->parent->right = node;

        }

        if (!prio_tree_left_empty(old)) {

                node->left = old->left;

                old->left->parent = node;

        }

        if (!prio_tree_right_empty(old)) {

                node->right = old->right;

                old->right->parent = node;

        }

        return old;

}

/*

 * Insert a prio_tree_node @node into a radix priority search tree @root. The

 * algorithm typically takes O(log n) time where 'log n' is the number of bits

 * required to represent the maximum heap_index. In the worst case, the algo

 * can take O((log n)^2) - check prio_tree_expand.

 *

 * If a prior node with same radix_index and heap_index is already found in

 * the tree, then returns the address of the prior node. Otherwise, inserts

 * @node into the tree and returns @node.

 */

struct prio_tree_node *prio_tree_insert(struct prio_tree_root *root,

                struct prio_tree_node *node)

{

        struct prio_tree_node *cur, *res = node;

        unsigned long radix_index, heap_index;

        unsigned long r_index, h_index, index, mask;

        int size_flag = 0;

        get_index(root, node, &radix_index, &heap_index);

        if (prio_tree_empty(root) ||

                        heap_index > prio_tree_maxindex(root->index_bits))

                return prio_tree_expand(root, node, heap_index);

        cur = root->prio_tree_node;

        mask = 1UL << (root->index_bits - 1);

        while (mask) {

                get_index(root, cur, &r_index, &h_index);

                if (r_index == radix_index && h_index == heap_index)

                        return cur;

                if (h_index < heap_index ||

                    (h_index == heap_index && r_index > radix_index)) {

                        struct prio_tree_node *tmp = node;

                        node = prio_tree_replace(root, cur, node);

                        cur = tmp;

                        /* swap indices */

                        index = r_index;

                        r_index = radix_index;

                        radix_index = index;

                        index = h_index;

                        h_index = heap_index;

                        heap_index = index;

                }

                if (size_flag)

                        index = heap_index - radix_index;

                else

                        index = radix_index;

                if (index & mask) {

                        if (prio_tree_right_empty(cur)) {

                                INIT_PRIO_TREE_NODE(node);

                                cur->right = node;

                                node->parent = cur;

                                return res;

                        } else

                                cur = cur->right;

                } else {

                        if (prio_tree_left_empty(cur)) {

                                INIT_PRIO_TREE_NODE(node);

                                cur->left = node;

                                node->parent = cur;

                                return res;

                        } else

                                cur = cur->left;

                }

                mask >>= 1;

                if (!mask) {

                        mask = 1UL << (BITS_PER_LONG - 1);

                        size_flag = 1;

                }

        }

        /* Should not reach here */

        BUG();

        return NULL;

}

/*

 * Remove a prio_tree_node @node from a radix priority search tree @root. The

 * algorithm takes O(log n) time where 'log n' is the number of bits required

 * to represent the maximum heap_index.

 */

void prio_tree_remove(struct prio_tree_root *root, struct prio_tree_node *node)

{

        struct prio_tree_node *cur;

        unsigned long r_index, h_index_right, h_index_left;

        cur = node;

        while (!prio_tree_left_empty(cur) || !prio_tree_right_empty(cur)) {

                if (!prio_tree_left_empty(cur))

                        get_index(root, cur->left, &r_index, &h_index_left);

                else {

                        cur = cur->right;

                        continue;

                }

                if (!prio_tree_right_empty(cur))

                        get_index(root, cur->right, &r_index, &h_index_right);

                else {

                        cur = cur->left;

                        continue;

                }

                /* both h_index_left and h_index_right cannot be 0 */

                if (h_index_left >= h_index_right)

                        cur = cur->left;

                else

                        cur = cur->right;

        }

        if (prio_tree_root(cur)) {

                BUG_ON(root->prio_tree_node != cur);

                __INIT_PRIO_TREE_ROOT(root, root->raw);

                return;

        }

        if (cur->parent->right == cur)

                cur->parent->right = cur->parent;

        else

                cur->parent->left = cur->parent;

        while (cur != node)

                cur = prio_tree_replace(root, cur->parent, cur);

}

/*

 * Following functions help to enumerate all prio_tree_nodes in the tree that

 * overlap with the input interval X [radix_index, heap_index]. The enumeration

 * takes O(log n + m) time where 'log n' is the height of the tree (which is

 * proportional to # of bits required to represent the maximum heap_index) and

 * 'm' is the number of prio_tree_nodes that overlap the interval X.

 */

static struct prio_tree_node *prio_tree_left(struct prio_tree_iter *iter,

                unsigned long *r_index, unsigned long *h_index)

{

        if (prio_tree_left_empty(iter->cur))

                return NULL;

        get_index(iter->root, iter->cur->left, r_index, h_index);

        if (iter->r_index <= *h_index) {

                iter->cur = iter->cur->left;

                iter->mask >>= 1;

                if (iter->mask) {

                        if (iter->size_level)

                                iter->size_level++;

                } else {

                        if (iter->size_level) {

                                BUG_ON(!prio_tree_left_empty(iter->cur));

                                BUG_ON(!prio_tree_right_empty(iter->cur));

                                iter->size_level++;

                                iter->mask = ULONG_MAX;

                        } else {

                                iter->size_level = 1;

                                iter->mask = 1UL << (BITS_PER_LONG - 1);

                        }

                }

                return iter->cur;

        }

        return NULL;

}

static struct prio_tree_node *prio_tree_right(struct prio_tree_iter *iter,

                unsigned long *r_index, unsigned long *h_index)

{

        unsigned long value;

        if (prio_tree_right_empty(iter->cur))

                return NULL;

        if (iter->size_level)

                value = iter->value;

        else

                value = iter->value | iter->mask;

        if (iter->h_index < value)

                return NULL;

        get_index(iter->root, iter->cur->right, r_index, h_index);

        if (iter->r_index <= *h_index) {

                iter->cur = iter->cur->right;

                iter->mask >>= 1;

                iter->value = value;

                if (iter->mask) {

                        if (iter->size_level)

                                iter->size_level++;

                } else {

                        if (iter->size_level) {

                                BUG_ON(!prio_tree_left_empty(iter->cur));

                                BUG_ON(!prio_tree_right_empty(iter->cur));

                                iter->size_level++;

                                iter->mask = ULONG_MAX;

                        } else {

                                iter->size_level = 1;

                                iter->mask = 1UL << (BITS_PER_LONG - 1);

                        }

                }

                return iter->cur;

        }

        return NULL;

}

static struct prio_tree_node *prio_tree_parent(struct prio_tree_iter *iter)

{

        iter->cur = iter->cur->parent;

        if (iter->mask == ULONG_MAX)

                iter->mask = 1UL;

        else if (iter->size_level == 1)

                iter->mask = 1UL;

        else

                iter->mask <<= 1;

        if (iter->size_level)

                iter->size_level--;

        if (!iter->size_level && (iter->value & iter->mask))

                iter->value ^= iter->mask;

        return iter->cur;

}

static inline int overlap(struct prio_tree_iter *iter,

                unsigned long r_index, unsigned long h_index)

{

        return iter->h_index >= r_index && iter->r_index <= h_index;

}

/*

 * prio_tree_first:

 *

 * Get the first prio_tree_node that overlaps with the interval [radix_index,

 * heap_index]. Note that always radix_index <= heap_index. We do a pre-order

 * traversal of the tree.

 */

static struct prio_tree_node *prio_tree_first(struct prio_tree_iter *iter)

{

        struct prio_tree_root *root;

        unsigned long r_index, h_index;

        INIT_PRIO_TREE_ITER(iter);

        root = iter->root;

        if (prio_tree_empty(root))

                return NULL;

        get_index(root, root->prio_tree_node, &r_index, &h_index);

        if (iter->r_index > h_index)

                return NULL;

        iter->mask = 1UL << (root->index_bits - 1);

        iter->cur = root->prio_tree_node;

        while (1) {

                if (overlap(iter, r_index, h_index))

                        return iter->cur;

                if (prio_tree_left(iter, &r_index, &h_index))

                        continue;

                if (prio_tree_right(iter, &r_index, &h_index))

                        continue;

                break;

        }

        return NULL;

}

/*

 * prio_tree_next:

 *

 * Get the next prio_tree_node that overlaps with the input interval in iter

 */

struct prio_tree_node *prio_tree_next(struct prio_tree_iter *iter)

{

        unsigned long r_index, h_index;

        if (iter->cur == NULL)

                return prio_tree_first(iter);

repeat:

        while (prio_tree_left(iter, &r_index, &h_index))

                if (overlap(iter, r_index, h_index))

                        return iter->cur;

        while (!prio_tree_right(iter, &r_index, &h_index)) {

                while (!prio_tree_root(iter->cur) &&

                                iter->cur->parent->right == iter->cur)

                        prio_tree_parent(iter);

                if (prio_tree_root(iter->cur))

                        return NULL;

                prio_tree_parent(iter);

        }

        if (overlap(iter, r_index, h_index))

                return iter->cur;

        goto repeat;

}