source: mainline/src/mm/buddy.c@ 2a9543d

/*
 * 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.
 */

#include <mm/buddy.h>
#include <mm/frame.h>
#include <mm/heap.h>
#include <arch/types.h>
#include <typedefs.h>
#include <list.h>
#include <debug.h>

/** Create buddy system
 *
 * Allocate memory for and initialize new buddy system.
 *
 * @param max_order The biggest allocable size will be 2^max_order.
 * @param op Operations for new buddy system.
 *
 * @return New buddy system.
 */
buddy_system_t *buddy_system_create(__u8 max_order, buddy_operations_t *op)
{
        buddy_system_t *b;
        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);

        /*
         * Allocate memory for structure describing the whole buddy system.
         */     
        b = (buddy_system_t *) early_malloc(sizeof(buddy_system_t));
        
        if (b) {
                /*
                 * Allocate memory for all orders this buddy system will work with.
                 */
                b->order = (link_t *) early_malloc(max_order * sizeof(link_t));
                if (!b->order) {
                        early_free(b);
                        return NULL;
                }
        
                for (i = 0; i < max_order; i++)
                        list_initialize(&b->order[i]);
        
                b->max_order = max_order;
                b->op = op;
        }
        
        return b;
}

/** Allocate block from buddy system.
 *
 * 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, __u8 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.
         */
        if (!list_empty(&b->order[i])) {
                res = b->order[i].next;
                list_remove(res);
                return res;
        }
        
        /*
         * If order i is already the maximal order,
         * the request cannot be satisfied.
         */
        if (i == b->max_order - 1)
                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(res);
        b->op->set_order(res, i);
        b->op->set_order(hlp, i);
        
        /*
         * Return the other half to buddy system.
         */
        buddy_system_free(b, hlp);
        
        return res;
        
}

/** Return block to buddy system.
 *
 * 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;
        __u8 i;
        
        /*
         * Determine block's order.
         */
        i = b->op->get_order(block);

        ASSERT(i < b->max_order);

        if (i != b->max_order - 1) {
                /*
                 * See if there is any buddy in the list of order i.
                 */
                buddy = b->op->find_buddy(block);
                if (buddy) {

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

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

}