source: mainline/kernel/generic/src/lib/ra.c@ 82cbf8c6

/*
 * Copyright (c) 2011 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 generic
 * @{
 */

/**
 * @file
 * @brief Resource allocator.
 *
 * This is a generic resource allocator, loosely based on the ideas presented
 * in chapter 4 of the following paper and further simplified:
 *
 *   Bonwick J., Adams J.: Magazines and Vmem: Extending the Slab Allocator to
 *   Many CPUs and Arbitrary Resources, USENIX 2001
 *
 */

#include <assert.h>
#include <lib/ra.h>
#include <typedefs.h>
#include <mm/slab.h>
#include <bitops.h>
#include <panic.h>
#include <adt/list.h>
#include <adt/hash.h>
#include <adt/hash_table.h>
#include <align.h>
#include <macros.h>
#include <synch/spinlock.h>

static slab_cache_t *ra_segment_cache;

/** Return the hash of the key stored in the item */
static size_t used_hash(const ht_link_t *item)
{
        ra_segment_t *seg = hash_table_get_inst(item, ra_segment_t, uh_link);
        return hash_mix(seg->base);
}

/** Return the hash of the key */
static size_t used_key_hash(void *key)
{
        uintptr_t *base = (uintptr_t *) key;
        return hash_mix(*base);
}

/** Return true if the key is equal to the item's lookup key */
static bool used_key_equal(void *key, const ht_link_t *item)
{
        uintptr_t *base = (sysarg_t *) key;
        ra_segment_t *seg = hash_table_get_inst(item, ra_segment_t, uh_link);
        return seg->base == *base;
}

static hash_table_ops_t used_ops = {
        .hash = used_hash,
        .key_hash = used_key_hash,
        .key_equal = used_key_equal
};

/** Calculate the segment size. */
static size_t ra_segment_size_get(ra_segment_t *seg)
{
        ra_segment_t *nextseg;

        nextseg = list_get_instance(seg->segment_link.next, ra_segment_t,
            segment_link);
        return nextseg->base - seg->base;
}

static ra_segment_t *ra_segment_create(uintptr_t base)
{
        ra_segment_t *seg;

        seg = slab_alloc(ra_segment_cache, FRAME_ATOMIC);
        if (!seg)
                return NULL;

        link_initialize(&seg->segment_link);
        link_initialize(&seg->fl_link);

        seg->base = base;
        seg->flags = 0;

        return seg;
}

static void ra_segment_destroy(ra_segment_t *seg)
{
        slab_free(ra_segment_cache, seg);
}

static ra_span_t *ra_span_create(uintptr_t base, size_t size)
{
        ra_span_t *span;
        ra_segment_t *seg, *lastseg;
        unsigned int i;

        span = (ra_span_t *) malloc(sizeof(ra_span_t), FRAME_ATOMIC);
        if (!span)
                return NULL;

        span->max_order = fnzb(size);
        span->base = base;
        span->size = size;

        span->free = (list_t *) malloc((span->max_order + 1) * sizeof(list_t),
            FRAME_ATOMIC);
        if (!span->free) {
                free(span);
                return NULL;
        }

        /*
         * Create a segment to represent the entire size of the span.
         */
        seg = ra_segment_create(base);
        if (!seg) {
                free(span->free);
                free(span);
                return NULL;
        }
        seg->flags = RA_SEGMENT_FREE;

        /*
         * The last segment will be used as a sentinel at the end of the
         * segment list so that it is possible to calculate the size for
         * all other segments. It will not be placed in any free list or
         * in the used segment hash and adjacent segments will not be
         * coalesced with it.
         */
        lastseg = ra_segment_create(base + size);
        if (!lastseg) {
                ra_segment_destroy(seg);
                free(span->free);
                free(span);
                return NULL;
        }

        link_initialize(&span->span_link);
        list_initialize(&span->segments);

        hash_table_create(&span->used, 0, 0, &used_ops);

        for (i = 0; i <= span->max_order; i++)
                list_initialize(&span->free[i]);

        /* Insert the first segment into the list of segments. */
        list_append(&seg->segment_link, &span->segments);
        /* Insert the last segment into the list of segments. */
        list_append(&lastseg->segment_link, &span->segments);

        /* Insert the first segment into the respective free list. */
        list_append(&seg->fl_link, &span->free[span->max_order]);

        return span;
}

/** Create an empty arena. */
ra_arena_t *ra_arena_create(void)
{
        ra_arena_t *arena;

        arena = (ra_arena_t *) malloc(sizeof(ra_arena_t), FRAME_ATOMIC);
        if (!arena)
                return NULL;

        irq_spinlock_initialize(&arena->lock, "arena_lock");
        list_initialize(&arena->spans);

        return arena;
}

/** Add a span to arena. */
bool ra_span_add(ra_arena_t *arena, uintptr_t base, size_t size)
{
        ra_span_t *span;

        span = ra_span_create(base, size);
        if (!span)
                return false;

        /* TODO: check for overlaps */
        irq_spinlock_lock(&arena->lock, true);
        list_append(&span->span_link, &arena->spans);
        irq_spinlock_unlock(&arena->lock, true);
        return true;
}

static bool
ra_span_alloc(ra_span_t *span, size_t size, size_t align, uintptr_t *base)
{
        /*
         * We need to add the maximum of align - 1 to be able to compensate for
         * the worst case unaligned segment.
         */
        size_t needed = size + align - 1;
        size_t order = ispwr2(needed) ? fnzb(needed) : fnzb(needed) + 1;
        ra_segment_t *pred = NULL;
        ra_segment_t *succ = NULL;

        /*
         * Find the free list of the smallest order which can satisfy this
         * request.
         */
        for (; order <= span->max_order; order++) {
                ra_segment_t *seg;
                uintptr_t newbase;

                if (list_empty(&span->free[order]))
                        continue;

                /* Take the first segment from the free list. */
                seg = list_get_instance(list_first(&span->free[order]),
                    ra_segment_t, fl_link);

                assert(seg->flags & RA_SEGMENT_FREE);

                /*
                 * See if we need to allocate new segments for the chopped-off
                 * parts of this segment.
                 */
                if (!IS_ALIGNED(seg->base, align)) {
                        pred = ra_segment_create(seg->base);
                        if (!pred) {
                                /*
                                 * Fail as we are unable to split the segment.
                                 */
                                break;
                        }
                        pred->flags |= RA_SEGMENT_FREE;
                }
                newbase = ALIGN_UP(seg->base, align);
                if (newbase + size != seg->base + ra_segment_size_get(seg)) {
                        assert(newbase + (size - 1) < seg->base +
                            (ra_segment_size_get(seg) - 1));
                        succ = ra_segment_create(newbase + size);
                        if (!succ) {
                                if (pred)
                                        ra_segment_destroy(pred);
                                /*
                                 * Fail as we are unable to split the segment.
                                 */
                                break;
                        }
                        succ->flags |= RA_SEGMENT_FREE;
                }
                
        
                /* Put unneeded parts back. */
                if (pred) {
                        size_t pred_order;

                        list_insert_before(&pred->segment_link,
                            &seg->segment_link);
                        pred_order = fnzb(ra_segment_size_get(pred));
                        list_append(&pred->fl_link, &span->free[pred_order]);
                }
                if (succ) {
                        size_t succ_order;

                        list_insert_after(&succ->segment_link,
                            &seg->segment_link);
                        succ_order = fnzb(ra_segment_size_get(succ));
                        list_append(&succ->fl_link, &span->free[succ_order]);
                }

                /* Now remove the found segment from the free list. */
                list_remove(&seg->fl_link);
                seg->base = newbase;
                seg->flags &= ~RA_SEGMENT_FREE;

                /* Hash-in the segment into the used hash. */
                hash_table_insert(&span->used, &seg->uh_link);

                *base = newbase;
                return true;
        }

        return false;
}

static void ra_span_free(ra_span_t *span, size_t base, size_t size)
{
        sysarg_t key = base;
        ht_link_t *link;
        ra_segment_t *seg;
        ra_segment_t *pred;
        ra_segment_t *succ;
        size_t order;

        /*
         * Locate the segment in the used hash table.
         */
        link = hash_table_find(&span->used, &key);
        if (!link) {
                panic("Freeing segment which is not known to be used (base=%"
                    PRIxn ", size=%" PRIdn ").", base, size);
        }
        seg = hash_table_get_inst(link, ra_segment_t, uh_link);

        /*
         * Hash out the segment.
         */
        hash_table_remove_item(&span->used, link);

        assert(!(seg->flags & RA_SEGMENT_FREE));
        assert(seg->base == base);
        assert(ra_segment_size_get(seg) == size);

        /*
         * Check whether the segment can be coalesced with its left neighbor.
         */
        if (list_first(&span->segments) != &seg->segment_link) {
                pred = hash_table_get_inst(seg->segment_link.prev,
                    ra_segment_t, segment_link);

                assert(pred->base < seg->base);

                if (pred->flags & RA_SEGMENT_FREE) {
                        /*
                         * The segment can be coalesced with its predecessor.
                         * Remove the predecessor from the free and segment
                         * lists, rebase the segment and throw the predecessor
                         * away.
                         */
                        list_remove(&pred->fl_link);
                        list_remove(&pred->segment_link);
                        seg->base = pred->base;
                        ra_segment_destroy(pred);
                }
        }

        /*
         * Check whether the segment can be coalesced with its right neighbor.
         */
        succ = hash_table_get_inst(seg->segment_link.next, ra_segment_t,
            segment_link);
        assert(succ->base > seg->base);
        if (succ->flags & RA_SEGMENT_FREE) {
                /*
                 * The segment can be coalesced with its successor.
                 * Remove the successor from the free and segment lists
                 * and throw it away.
                 */
                list_remove(&succ->fl_link);
                list_remove(&succ->segment_link);
                ra_segment_destroy(succ);
        }

        /* Put the segment on the appropriate free list. */
        seg->flags |= RA_SEGMENT_FREE;
        order = fnzb(ra_segment_size_get(seg));
        list_append(&seg->fl_link, &span->free[order]);
}

/** Allocate resources from arena. */
bool
ra_alloc(ra_arena_t *arena, size_t size, size_t alignment, uintptr_t *base)
{
        bool success = false;

        assert(size >= 1);
        assert(alignment >= 1);
        assert(ispwr2(alignment));

        irq_spinlock_lock(&arena->lock, true);
        list_foreach(arena->spans, span_link, ra_span_t, span) {
                success = ra_span_alloc(span, size, alignment, base);
                if (success)
                        break;
        }
        irq_spinlock_unlock(&arena->lock, true);

        return success;
}

/* Return resources to arena. */
void ra_free(ra_arena_t *arena, uintptr_t base, size_t size)
{
        irq_spinlock_lock(&arena->lock, true);
        list_foreach(arena->spans, span_link, ra_span_t, span) {
                if (iswithin(span->base, span->size, base, size)) {
                        ra_span_free(span, base, size);
                        irq_spinlock_unlock(&arena->lock, true);
                        return;
                }
        }
        irq_spinlock_unlock(&arena->lock, true);

        panic("Freeing to wrong arena (base=%" PRIxn ", size=%" PRIdn ").",
            base, size);
}

void ra_init(void)
{
        ra_segment_cache = slab_cache_create("ra_segment_t",
            sizeof(ra_segment_t), 0, NULL, NULL, SLAB_CACHE_MAGDEFERRED);
}

/** @}
 */