source: mainline/kernel/generic/src/mm/buddy.c@ 181a746

/*
 * Copyright (c) 2005 Jakub Jermar
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/** @addtogroup genericmm
 * @{
 */

/**
 * @file
 * @brief       Buddy allocator framework.
 *
 * This file contains buddy system allocator framework.
 * Specialized functions are needed for this abstract framework to be useful.
 */

#include <mm/buddy.h>
#include <mm/frame.h>
#include <typedefs.h>
#include <debug.h>
#include <print.h>
#include <macros.h>

/** Return size needed for the buddy configuration data. */
size_t buddy_conf_size(size_t max_order)
{
        return sizeof(buddy_system_t) + (max_order + 1) * sizeof(link_t);
}


/** Create buddy system.
 *
 * Allocate memory for and initialize new buddy system.
 *
 * @param b             Preallocated buddy system control data.
 * @param max_order     The biggest allocable size will be 2^max_order.
 * @param op            Operations for new buddy system.
 * @param data          Pointer to be used by implementation.
 *
 * @return              New buddy system.
 */
void
buddy_system_create(buddy_system_t *b, uint8_t max_order,
    buddy_system_operations_t *op, void *data)
{
        int i;

        ASSERT(max_order < BUDDY_SYSTEM_INNER_BLOCK);

        ASSERT(op->find_buddy);
        ASSERT(op->set_order);
        ASSERT(op->get_order);
        ASSERT(op->bisect);
        ASSERT(op->coalesce);
        ASSERT(op->mark_busy);

        /*
         * Use memory after our own structure.
         */
        b->order = (list_t *) (&b[1]);
        
        for (i = 0; i <= max_order; i++)
                list_initialize(&b->order[i]);

        b->max_order = max_order;
        b->op = op;
        b->data = data;
}

/** Check if buddy system can allocate block.
 *
 * @param b             Buddy system pointer.
 * @param i             Size of the block (2^i).
 *
 * @return              True if block can be allocated.
 */
bool buddy_system_can_alloc(buddy_system_t *b, uint8_t i)
{
        uint8_t k;
        
        /*
         * If requested block is greater then maximal block
         * we know immediatly that we cannot satisfy the request.
         */
        if (i > b->max_order)
                return false;

        /*
         * Check if any bigger or equal order has free elements
         */
        for (k = i; k <= b->max_order; k++) {
                if (!list_empty(&b->order[k])) {
                        return true;
                }
        }
        
        return false;
}

/** Allocate PARTICULAR block from buddy system.
 *
 * @return              Block of data or NULL if no such block was found.
 */
link_t *buddy_system_alloc_block(buddy_system_t *b, link_t *block)
{
        link_t *left,*right, *tmp;
        uint8_t order;

        left = b->op->find_block(b, block, BUDDY_SYSTEM_INNER_BLOCK);
        ASSERT(left);
        list_remove(left);
        while (1) {
                if (!b->op->get_order(b, left)) {
                        b->op->mark_busy(b, left);
                        return left;
                }
                
                order = b->op->get_order(b, left);

                right = b->op->bisect(b, left);
                b->op->set_order(b, left, order - 1);
                b->op->set_order(b, right, order - 1);

                tmp = b->op->find_block(b, block, BUDDY_SYSTEM_INNER_BLOCK);

                if (tmp == right) {
                        right = left;
                        left = tmp;
                } 
                ASSERT(tmp == left);
                b->op->mark_busy(b, left);
                buddy_system_free(b, right);
                b->op->mark_available(b, left);
        }
}

/** Allocate block from buddy system.
 *
 * @param b             Buddy system pointer.
 * @param i             Returned block will be 2^i big.
 *
 * @return              Block of data represented by link_t.
 */
link_t *buddy_system_alloc(buddy_system_t *b, uint8_t i)
{
        link_t *res, *hlp;

        ASSERT(i <= b->max_order);

        /*
         * If the list of order i is not empty,
         * the request can be immediatelly satisfied.
         */
        res = list_first(&b->order[i]);
        if (res != NULL) {
                list_remove(res);
                b->op->mark_busy(b, res);
                return res;
        }
        /*
         * If order i is already the maximal order,
         * the request cannot be satisfied.
         */
        if (i == b->max_order)
                return NULL;

        /*
         * Try to recursively satisfy the request from higher order lists.
         */     
        hlp = buddy_system_alloc(b, i + 1);
        
        /*
         * The request could not be satisfied
         * from higher order lists.
         */
        if (!hlp)
                return NULL;
                
        res = hlp;
        
        /*
         * Bisect the block and set order of both of its parts to i.
         */
        hlp = b->op->bisect(b, res);
        b->op->set_order(b, res, i);
        b->op->set_order(b, hlp, i);
        
        /*
         * Return the other half to buddy system. Mark the first part
         * full, so that it won't coalesce again.
         */
        b->op->mark_busy(b, res);
        buddy_system_free(b, hlp);
        
        return res;
}

/** Return block to buddy system.
 *
 * @param b             Buddy system pointer.
 * @param block         Block to return.
 */
void buddy_system_free(buddy_system_t *b, link_t *block)
{
        link_t *buddy, *hlp;
        uint8_t i;

        /*
         * Determine block's order.
         */
        i = b->op->get_order(b, block);

        ASSERT(i <= b->max_order);

        if (i != b->max_order) {
                /*
                 * See if there is any buddy in the list of order i.
                 */
                buddy = b->op->find_buddy(b, block);
                if (buddy) {

                        ASSERT(b->op->get_order(b, buddy) == i);
                        /*
                         * Remove buddy from the list of order i.
                         */
                        list_remove(buddy);
                
                        /*
                         * Invalidate order of both block and buddy.
                         */
                        b->op->set_order(b, block, BUDDY_SYSTEM_INNER_BLOCK);
                        b->op->set_order(b, buddy, BUDDY_SYSTEM_INNER_BLOCK);
                
                        /*
                         * Coalesce block and buddy into one block.
                         */
                        hlp = b->op->coalesce(b, block, buddy);

                        /*
                         * Set order of the coalesced block to i + 1.
                         */
                        b->op->set_order(b, hlp, i + 1);

                        /*
                         * Recursively add the coalesced block to the list of
                         * order i + 1.
                         */
                        buddy_system_free(b, hlp);
                        return;
                }
        }

        /*
         * Insert block into the list of order i.
         */
        list_append(block, &b->order[i]);
}

/** @}
 */