Function rt_slab_alloc

src/slab.c:490–655

* @brief This function will allocate a block from slab object. * * @note the RT_NULL is returned if * - the nbytes is less than zero. * - there is no nbytes sized memory valid in system. * * @param m the slab memory management object. * * @param size is the size of memory to be allocated. * * @return the allocated memory. */

 * @return the allocated memory.
 */
void *rt_slab_alloc(rt_slab_t m, rt_size_t size)
{
    struct rt_slab_zone *z;
    rt_int32_t zi;
    struct rt_slab_chunk *chunk;
    struct rt_slab_memusage *kup;
    struct rt_slab *slab = (struct rt_slab *)m;

    /* zero size, return RT_NULL */
    if (size == 0)
        return RT_NULL;

    /*
     * Handle large allocations directly.  There should not be very many of
     * these so performance is not a big issue.
     */
    if (size >= slab->zone_limit)
    {
        size = RT_ALIGN(size, RT_MM_PAGE_SIZE);

        chunk = rt_slab_page_alloc(m, size >> RT_MM_PAGE_BITS);
        if (chunk == RT_NULL)
            return RT_NULL;

        /* set kup */
        kup = btokup(chunk);
        kup->type = PAGE_TYPE_LARGE;
        kup->size = size >> RT_MM_PAGE_BITS;

        LOG_D("alloc a large memory 0x%x, page cnt %d, kup %d",
              size,
              size >> RT_MM_PAGE_BITS,
              ((rt_uintptr_t)chunk - slab->heap_start) >> RT_MM_PAGE_BITS);
        /* mem stat */
        slab->parent.used += size;
        if (slab->parent.used > slab->parent.max)
            slab->parent.max = slab->parent.used;
        return chunk;
    }

    /*
     * Attempt to allocate out of an existing zone.  First try the free list,
     * then allocate out of unallocated space.  If we find a good zone move
     * it to the head of the list so later allocations find it quickly
     * (we might have thousands of zones in the list).
     *
     * Note: zoneindex() will panic of size is too large.
     */
    zi = zoneindex(&size);
    RT_ASSERT(zi < RT_SLAB_NZONES);

    LOG_D("try to alloc 0x%x on zone: %d", size, zi);

    if ((z = slab->zone_array[zi]) != RT_NULL)
    {
        RT_ASSERT(z->z_nfree > 0);

        /* Remove us from the zone_array[] when we become full */