rt-thread/src/slab.c

/*
 * File      : slab.c
 * This file is part of RT-Thread RTOS
 * COPYRIGHT (C) 2008 - 2009, RT-Thread Development Team
 *
 * The license and distribution terms for this file may be
 * found in the file LICENSE in this distribution or at
 * http://www.rt-thread.org/license/LICENSE
 *
 * Change Logs:
 * Date           Author       Notes
 * 2008-07-12     Bernard      the first version
 * 2010-07-13     Bernard      fix RT_ALIGN issue found by kuronca
 */

/*
 * KERN_SLABALLOC.C	- Kernel SLAB memory allocator
 *
 * Copyright (c) 2003,2004 The DragonFly Project.  All rights reserved.
 *
 * This code is derived from software contributed to The DragonFly Project
 * by Matthew Dillon <dillon@backplane.com>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. 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.
 * 3. Neither the name of The DragonFly Project nor the names of its
 *    contributors may be used to endorse or promote products derived
 *    from this software without specific, prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * ``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
 * COPYRIGHT HOLDERS OR CONTRIBUTORS 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 <rthw.h>
#include <rtthread.h>

/* #define RT_SLAB_DEBUG */

#if defined (RT_USING_HEAP) && defined (RT_USING_SLAB)
#ifdef RT_USING_HOOK
static void (*rt_malloc_hook)(void *ptr, rt_size_t size);
static void (*rt_free_hook)(void *ptr);

/**
 * @addtogroup Hook
 */
/*@{*/

/**
 * This function will set a hook function, which will be invoked when a memory
 * block is allocated from heap memory.
 *
 * @param hook the hook function
 */
void rt_malloc_sethook(void (*hook)(void *ptr, rt_size_t size))
{
	rt_malloc_hook = hook;
}

/**
 * This function will set a hook function, which will be invoked when a memory
 * block is released to heap memory.
 *
 * @param hook the hook function
 */
void rt_free_sethook(void (*hook)(void *ptr))
{
	rt_free_hook = hook;
}

/*@}*/

#endif

/*
 * slab allocator implementation
 *
 * A slab allocator reserves a ZONE for each chunk size, then lays the
 * chunks out in an array within the zone.  Allocation and deallocation
 * is nearly instantanious, and fragmentation/overhead losses are limited
 * to a fixed worst-case amount.
 *
 * The downside of this slab implementation is in the chunk size
 * multiplied by the number of zones.  ~80 zones * 128K = 10MB of VM per cpu.
 * In a kernel implementation all this memory will be physical so
 * the zone size is adjusted downward on machines with less physical
 * memory.  The upside is that overhead is bounded... this is the *worst*
 * case overhead.
 *
 * Slab management is done on a per-cpu basis and no locking or mutexes
 * are required, only a critical section.  When one cpu frees memory
 * belonging to another cpu's slab manager an asynchronous IPI message
 * will be queued to execute the operation.   In addition, both the
 * high level slab allocator and the low level zone allocator optimize
 * M_ZERO requests, and the slab allocator does not have to pre initialize
 * the linked list of chunks.
 *
 * XXX Balancing is needed between cpus.  Balance will be handled through
 * asynchronous IPIs primarily by reassigning the z_Cpu ownership of chunks.
 *
 * XXX If we have to allocate a new zone and M_USE_RESERVE is set, use of
 * the new zone should be restricted to M_USE_RESERVE requests only.
 *
 *	Alloc Size	Chunking        Number of zones
 *	0-127		8				16
 *	128-255		16				8
 *	256-511		32				8
 *	512-1023	64				8
 *	1024-2047	128				8
 *	2048-4095	256				8
 *	4096-8191	512				8
 *	8192-16383	1024			8
 *	16384-32767	2048			8
 *	(if RT_MM_PAGE_SIZE is 4K the maximum zone allocation is 16383)
 *
 *	Allocations >= zone_limit go directly to kmem.
 *
 *			API REQUIREMENTS AND SIDE EFFECTS
 *
 *    To operate as a drop-in replacement to the FreeBSD-4.x malloc() we
 *    have remained compatible with the following API requirements:
 *
 *    + small power-of-2 sized allocations are power-of-2 aligned (kern_tty)
 *    + all power-of-2 sized allocations are power-of-2 aligned (twe)
 *    + malloc(0) is allowed and returns non-RT_NULL (ahc driver)
 *    + ability to allocate arbitrarily large chunks of memory
 */

/*
 * Chunk structure for free elements
 */
typedef struct slab_chunk
{
    struct slab_chunk *c_next;
} slab_chunk;

/*
 * The IN-BAND zone header is placed at the beginning of each zone.
 */
typedef struct slab_zone {
    rt_int32_t	z_magic;		/* magic number for sanity check */
    rt_int32_t	z_nfree;		/* total free chunks / ualloc space in zone */
    rt_int32_t	z_nmax;			/* maximum free chunks */

    struct slab_zone *z_next;	/* zoneary[] link if z_nfree non-zero */
    rt_uint8_t	*z_baseptr;		/* pointer to start of chunk array */

	rt_int32_t	z_uindex;		/* current initial allocation index */
    rt_int32_t	z_chunksize;	/* chunk size for validation */

	rt_int32_t	z_zoneindex;	/* zone index */
    slab_chunk	*z_freechunk;	/* free chunk list */
} slab_zone;

#define ZALLOC_SLAB_MAGIC		0x51ab51ab
#define ZALLOC_ZONE_LIMIT		(16 * 1024)		/* max slab-managed alloc */
#define ZALLOC_MIN_ZONE_SIZE	(32 * 1024)		/* minimum zone size */
#define ZALLOC_MAX_ZONE_SIZE	(128 * 1024)	/* maximum zone size */
#define NZONES					72				/* number of zones */
#define ZONE_RELEASE_THRESH		2				/* threshold number of zones */

static slab_zone *zone_array[NZONES];	/* linked list of zones NFree > 0 */
static slab_zone *zone_free;			/* whole zones that have become free */

static int zone_free_cnt;
static int zone_size;
static int zone_limit;
static int zone_page_cnt;

#ifdef RT_MEM_STATS
/* some statistical variable */
static rt_uint32_t rt_mem_allocated = 0;
static rt_uint32_t rt_mem_zone = 0;
static rt_uint32_t rt_mem_page_allocated = 0;
#endif

/*
 * Misc constants.  Note that allocations that are exact multiples of
 * RT_MM_PAGE_SIZE, or exceed the zone limit, fall through to the kmem module.
 */
#define MIN_CHUNK_SIZE		8		/* in bytes */
#define MIN_CHUNK_MASK		(MIN_CHUNK_SIZE - 1)

/*
 * Array of descriptors that describe the contents of each page
 */
#define PAGE_TYPE_FREE		0x00
#define PAGE_TYPE_SMALL		0x01
#define PAGE_TYPE_LARGE		0x02
struct memusage {
	rt_uint32_t type:2 ;		/* page type */
	rt_uint32_t	size:30;		/* pages allocated or offset from zone */
};
static struct memusage *memusage = RT_NULL;
#define btokup(addr)	(&memusage[((rt_uint32_t)(addr) - heap_start) >> RT_MM_PAGE_BITS])

static rt_uint32_t heap_start, heap_end;

/* page allocator */
struct rt_page_head
{
	struct rt_page_head *next;		/* next valid page */
	rt_size_t page;					/* number of page  */

	/* dummy */
	char dummy[RT_MM_PAGE_SIZE - (sizeof(struct rt_page_head*) + sizeof (rt_size_t))];
};
static struct rt_page_head *rt_page_list;

static void *rt_page_alloc(rt_size_t npages)
{
	struct rt_page_head *b, *n;
	struct rt_page_head **prev;

	RT_ASSERT(npages != 0);

	for (prev = &rt_page_list; (b = *prev) != RT_NULL; prev = &(b->next))
	{
		if (b->page > npages)
		{
			/* splite pages */
			n = b + npages;
			n->next = b->next;
			n->page = b->page - npages;
			*prev = n;
			break;
		}

		if (b->page == npages)
		{
			/* this node fit, remove this node */
			*prev = b->next;
			break;
		}
	}

	return b;
}

static void rt_page_free(void *addr, rt_size_t npages)
{
	struct rt_page_head *b, *n;
	struct rt_page_head **prev;

	RT_ASSERT(addr != RT_NULL);
	RT_ASSERT((rt_uint32_t)addr % RT_MM_PAGE_SIZE == 0);
	RT_ASSERT(npages != 0);

	n = (struct rt_page_head *)addr;

	for (prev = &rt_page_list; (b = *prev) != RT_NULL; prev = &(b->next))
	{
		RT_ASSERT(b->page > 0);
		RT_ASSERT(b > n || b + b->page <= n);

		if (b + b->page == n)
		{
			if (b + (b->page += npages) == b->next)
			{
				b->page += b->next->page;
				b->next  = b->next->next;
			}

			return;
		}

		if (b == n + npages)
		{
			n->page = b->page + npages;
			n->next = b->next;
			*prev = n;

			return;
		}

		if (b > n + npages) break;
	}

	n->page = npages;
	n->next = b;
	*prev = n;
}

/*
 * Initialize the page allocator
 */
static void rt_page_init(void* addr, rt_size_t npages)
{
	RT_ASSERT(addr != RT_NULL);
	RT_ASSERT(npages != 0);

	rt_page_list = RT_NULL;
	rt_page_free(addr, npages);
}

/**
 * @ingroup SystemInit
 *
 * This function will init system heap
 *
 * @param begin_addr the beginning address of system page
 * @param end_addr the end address of system page
 *
 */
void rt_system_heap_init(void *begin_addr, void* end_addr)
{
	rt_uint32_t limsize, npages;

	/* align begin and end addr to page */
	heap_start	= RT_ALIGN((rt_uint32_t)begin_addr, RT_MM_PAGE_SIZE);
	heap_end	= RT_ALIGN_DOWN((rt_uint32_t)end_addr, RT_MM_PAGE_SIZE);

	limsize = heap_end - heap_start;
	npages = limsize / RT_MM_PAGE_SIZE;

#ifdef RT_SLAB_DEBUG
	rt_kprintf("heap[0x%x - 0x%x], size 0x%x, 0x%x pages\n", heap_start, heap_end, limsize, npages);
#endif

	/* init pages */
	rt_page_init((void*)heap_start, npages);

	/* calculate zone size */
	zone_size = ZALLOC_MIN_ZONE_SIZE;
	while (zone_size < ZALLOC_MAX_ZONE_SIZE && (zone_size << 1) < (limsize/1024))
		zone_size <<= 1;

	zone_limit = zone_size / 4;
	if (zone_limit > ZALLOC_ZONE_LIMIT) zone_limit = ZALLOC_ZONE_LIMIT;

	zone_page_cnt = zone_size / RT_MM_PAGE_SIZE;

#ifdef RT_SLAB_DEBUG
	rt_kprintf("zone size 0x%x, zone page count 0x%x\n", zone_size, zone_page_cnt);
#endif

	/* allocate memusage array */
	limsize = npages * sizeof(struct memusage);
	limsize = RT_ALIGN(limsize, RT_MM_PAGE_SIZE);
	memusage = rt_page_alloc(limsize/RT_MM_PAGE_SIZE);

#ifdef RT_SLAB_DEBUG
	rt_kprintf("memusage 0x%x, size 0x%x\n", (rt_uint32_t)memusage, limsize);
#endif
}

/*
 * Calculate the zone index for the allocation request size and set the
 * allocation request size to that particular zone's chunk size.
 */
rt_inline int zoneindex(rt_uint32_t *bytes)
{
	rt_uint32_t n = (rt_uint32_t)*bytes;	/* unsigned for shift opt */

	if (n < 128)
	{
		*bytes = n = (n + 7) & ~7;
		return(n / 8 - 1);		/* 8 byte chunks, 16 zones */
	}
	if (n < 256)
	{
		*bytes = n = (n + 15) & ~15;
		return(n / 16 + 7);
	}
	if (n < 8192)
	{
		if (n < 512)
		{
			*bytes = n = (n + 31) & ~31;
			return(n / 32 + 15);
		}
		if (n < 1024)
		{
			*bytes = n = (n + 63) & ~63;
			return(n / 64 + 23);
		}
		if (n < 2048)
		{
			*bytes = n = (n + 127) & ~127;
			return(n / 128 + 31);
		}
		if (n < 4096)
		{
			*bytes = n = (n + 255) & ~255;
			return(n / 256 + 39);
		}
		*bytes = n = (n + 511) & ~511;
		return(n / 512 + 47);
	}
	if (n < 16384)
	{
		*bytes = n = (n + 1023) & ~1023;
		return(n / 1024 + 55);
	}

	rt_kprintf("Unexpected byte count %d", n);
	return 0;
}

/**
 * @addtogroup MM
 */

/*@{*/

/**
 * This function will allocate a block from system heap memory.
 * - If the nbytes is less than zero,
 * or
 * - If there is no nbytes sized memory valid in system,
 * the RT_NULL is returned.
 *
 * @param size the size of memory to be allocated
 *
 * @return the allocated memory
 *
 */
void *rt_malloc(rt_size_t size)
{
	slab_zone *z;
	rt_int32_t zi;
	slab_chunk *chunk;
	rt_base_t interrupt_level;
	struct memusage *kup;

	/* 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 >= zone_limit)
	{
		size = RT_ALIGN(size, RT_MM_PAGE_SIZE);

		chunk = rt_page_alloc(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;

#ifdef RT_SLAB_DEBUG
		rt_kprintf("malloc a large memory 0x%x, page cnt %d, kup %d\n",
			size,
			size >> RT_MM_PAGE_BITS,
			((rt_uint32_t)chunk - heap_start) >> RT_MM_PAGE_BITS);
#endif

		/* lock interrupt */
		interrupt_level = rt_hw_interrupt_disable();
		goto done;
	}

	/*
	 * 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 < NZONES);

#ifdef RT_SLAB_DEBUG
	rt_kprintf("try to malloc 0x%x on zone: %d\n", size, zi);
#endif

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

		/* Remove us from the zone_array[] when we become empty */
		if (--z->z_nfree == 0)
		{
			zone_array[zi] = z->z_next;
			z->z_next = RT_NULL;
		}

		/*
		 * No chunks are available but nfree said we had some memory, so
		 * it must be available in the never-before-used-memory area
		 * governed by uindex.  The consequences are very serious if our zone
		 * got corrupted so we use an explicit rt_kprintf rather then a KASSERT.
		 */
		if (z->z_uindex + 1 != z->z_nmax)
		{
			z->z_uindex = z->z_uindex + 1;
			chunk = (slab_chunk *)(z->z_baseptr + z->z_uindex * size);
		}
		else
		{
			/* find on free chunk list */
			chunk = z->z_freechunk;

			/* remove this chunk from list */
			z->z_freechunk = z->z_freechunk->c_next;
		}

		goto done;
	}

	/*
	 * If all zones are exhausted we need to allocate a new zone for this
	 * index.
	 *
	 * At least one subsystem, the tty code (see CROUND) expects power-of-2
	 * allocations to be power-of-2 aligned.  We maintain compatibility by
	 * adjusting the base offset below.
	 */
	{
		rt_int32_t off;

		if ((z = zone_free) != RT_NULL)
		{
			/* remove zone from free zone list */
			zone_free = z->z_next;
			--zone_free_cnt;
		}
		else
		{
			/* allocate a zone from page */
			z = rt_page_alloc(zone_size / RT_MM_PAGE_SIZE);
			if (z == RT_NULL) goto fail;

#ifdef RT_SLAB_DEBUG
			rt_kprintf("alloc a new zone: 0x%x\n", (rt_uint32_t)z);
#endif

			/* set message usage */
			for (off = 0, kup = btokup(z); off < zone_page_cnt; off ++)
			{
				kup->type = PAGE_TYPE_SMALL;
				kup->size = off;

				kup ++;
			}
		}

		/* clear to zero */
		rt_memset(z, 0, sizeof(slab_zone));

		/* offset of slab zone struct in zone */
		off = sizeof(slab_zone);

		/*
		 * Guarentee power-of-2 alignment for power-of-2-sized chunks.
		 * Otherwise just 8-byte align the data.
		 */
		if ((size | (size - 1)) + 1 == (size << 1))
			off = (off + size - 1) & ~(size - 1);
		else
			off = (off + MIN_CHUNK_MASK) & ~MIN_CHUNK_MASK;

		z->z_magic = ZALLOC_SLAB_MAGIC;
		z->z_zoneindex	= zi;
		z->z_nmax		= (zone_size - off) / size;
		z->z_nfree		= z->z_nmax - 1;
		z->z_baseptr	= (rt_uint8_t*)z + off;
		z->z_uindex		= 0;
		z->z_chunksize	= size;

		chunk = (slab_chunk *)(z->z_baseptr + z->z_uindex * size);

		/* link to zone array */
		z->z_next = zone_array[zi];
		zone_array[zi] = z;
	}

done:
	rt_hw_interrupt_enable(interrupt_level);

#ifdef RT_USING_HOOK
	if (rt_malloc_hook != RT_NULL) rt_malloc_hook((char*)chunk, size);
#endif

	return chunk;

fail:
	rt_hw_interrupt_enable(interrupt_level);
	return RT_NULL;
}

/**
 * This function will change the size of previously allocated memory block.
 *
 * @param ptr the previously allocated memory block
 * @param size the new size of memory block
 *
 * @return the allocated memory
 */
void *rt_realloc(void *ptr, rt_size_t size)
{
	void *nptr;
	slab_zone *z;
	struct memusage *kup;

	if (ptr == RT_NULL) return rt_malloc(size);
	if (size == 0)
	{
		rt_free(ptr);
		return RT_NULL;
	}

	/*
	 * Get the original allocation's zone.  If the new request winds up
	 * using the same chunk size we do not have to do anything.
	 */
	kup = btokup((rt_uint32_t)ptr & ~RT_MM_PAGE_MASK);
	if (kup->type == PAGE_TYPE_LARGE)
	{
		rt_size_t osize;

		osize = kup->size << RT_MM_PAGE_BITS;
		if ((nptr = rt_malloc(size)) == RT_NULL) return RT_NULL;
		rt_memcpy(nptr, ptr, size > osize? osize : size);
		rt_free(ptr);

		return nptr;
	}
	else if (kup->type == PAGE_TYPE_SMALL)
	{
		z = (slab_zone*)(((rt_uint32_t)ptr & ~RT_MM_PAGE_MASK) - kup->size * RT_MM_PAGE_SIZE);
		RT_ASSERT(z->z_magic == ZALLOC_SLAB_MAGIC);

		zoneindex(&size);
		if (z->z_chunksize == size) return(ptr); /* same chunk */

		/*
		 * Allocate memory for the new request size.  Note that zoneindex has
		 * already adjusted the request size to the appropriate chunk size, which
		 * should optimize our bcopy().  Then copy and return the new pointer.
		 */
		if ((nptr = rt_malloc(size)) == RT_NULL) return RT_NULL;

		rt_memcpy(nptr, ptr, size > z->z_chunksize? z->z_chunksize : size);
		rt_free(ptr);

		return nptr;
	}

	return RT_NULL;
}

/**
 * This function will contiguously allocate enough space for count objects
 * that are size bytes of memory each and returns a pointer to the allocated
 * memory.
 *
 * The allocated memory is filled with bytes of value zero.
 *
 * @param count number of objects to allocate
 * @param size size of the objects to allocate
 *
 * @return pointer to allocated memory / NULL pointer if there is an error
 */
void *rt_calloc(rt_size_t count, rt_size_t size)
{
	void *p;

	/* allocate 'count' objects of size 'size' */
	p = rt_malloc(count * size);

	/* zero the memory */
	if (p) rt_memset(p, 0, count * size);

	return p;
}

/**
 * This function will release the previously allocated memory block by rt_malloc.
 * The released memory block is taken back to system heap.
 *
 * @param ptr the address of memory which will be released
 */
void rt_free(void *ptr)
{
	slab_zone *z;
	slab_chunk *chunk;
	struct memusage *kup;
	rt_base_t interrupt_level;

	/* free a RT_NULL pointer */
	if (ptr == RT_NULL) return ;

#ifdef RT_USING_HOOK
	if (rt_free_hook != RT_NULL) rt_free_hook(ptr);
#endif

	/* get memory usage */
#ifdef RT_SLAB_DEBUG
	rt_uint32 addr = ((rt_uint32_t)ptr & ~RT_MM_PAGE_MASK);
	rt_kprintf("free a memory 0x%x and align to 0x%x, kup index %d\n",
		(rt_uint32_t)ptr,
		(rt_uint32_t)addr,
		((rt_uint32_t)(addr) - heap_start) >> RT_MM_PAGE_BITS);
#endif

	kup = btokup((rt_uint32_t)ptr & ~RT_MM_PAGE_MASK);
	/* release large allocation */
	if (kup->type == PAGE_TYPE_LARGE)
	{
		rt_uint32_t size;

		/* clear page counter */
		interrupt_level = rt_hw_interrupt_disable();
		size = kup->size;
		kup->size = 0;
		rt_hw_interrupt_enable(interrupt_level);

#ifdef RT_SLAB_DEBUG
		rt_kprintf("free large memory block 0x%x, page count %d\n", (rt_uint32_t)ptr, size);
#endif

		/* free this page */
		rt_page_free(ptr, size);
		return;
	}

	/* zone case. get out zone. */
	z = (slab_zone*)(((rt_uint32_t)ptr & ~RT_MM_PAGE_MASK) - kup->size * RT_MM_PAGE_SIZE);
	RT_ASSERT(z->z_magic == ZALLOC_SLAB_MAGIC);

	interrupt_level = rt_hw_interrupt_disable();
	chunk = (slab_chunk*)ptr;
	chunk->c_next = z->z_freechunk;
	z->z_freechunk = chunk;

	/*
	 * Bump the number of free chunks.  If it becomes non-zero the zone
	 * must be added back onto the appropriate list.
	 */
	if (z->z_nfree++ == 0)
	{
		z->z_next = zone_array[z->z_zoneindex];
		zone_array[z->z_zoneindex] = z;
	}

	/*
	 * If the zone becomes totally free, and there are other zones we
	 * can allocate from, move this zone to the FreeZones list.  Since
	 * this code can be called from an IPI callback, do *NOT* try to mess
	 * with kernel_map here.  Hysteresis will be performed at malloc() time.
	 */
	if (z->z_nfree == z->z_nmax &&
		(z->z_next || zone_array[z->z_zoneindex] != z))
	{
		slab_zone **pz;

#ifdef RT_SLAB_DEBUG
		rt_kprintf("free zone 0x%x\n", (rt_uint32_t)z, z->z_zoneindex);
#endif

		/* remove zone from zone array list */
		for (pz = &zone_array[z->z_zoneindex]; z != *pz; pz = &(*pz)->z_next) ;
		*pz = z->z_next;

		/* reset zone */
		z->z_magic = -1;

		/* insert to free zone list */
		z->z_next = zone_free;
		zone_free = z;

		++zone_free_cnt;

		/* release zone to page allocator */
		if (zone_free_cnt > ZONE_RELEASE_THRESH)
		{
			register rt_base_t i;

			z = zone_free;
			zone_free = z->z_next;
			--zone_free_cnt;

			/* set message usage */
			for (i = 0, kup = btokup(z); i < zone_page_cnt; i ++)
			{
				kup->type = PAGE_TYPE_FREE;
				kup->size = 0;
				kup ++;
			}

			/* release pages */
			rt_page_free(z, zone_size);
		}
	}
	rt_hw_interrupt_enable(interrupt_level);
}

/*@}*/

#endif