/*
* Copyright (C) 2006 Ondrej Palkovsky
* 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.
*/
/*
* The SLAB allocator is closely modelled after Opensolaris SLAB allocator
* http://www.usenix.org/events/usenix01/full_papers/bonwick/bonwick_html/
*
* with the following exceptions:
* - empty SLABS are deallocated immediately
* (in Linux they are kept in linked list, in Solaris ???)
* - empty magazines are deallocated when not needed
* (in Solaris they are held in linked list in slab cache)
*
* Following features are not currently supported but would be easy to do:
* - cache coloring
* - dynamic magazine growing (different magazine sizes are already
* supported, but we would need to adjust allocating strategy)
*
* The SLAB allocator supports per-CPU caches ('magazines') to facilitate
* good SMP scaling.
*
* When a new object is being allocated, it is first checked, if it is
* available in CPU-bound magazine. If it is not found there, it is
* allocated from CPU-shared SLAB - if partial full is found, it is used,
* otherwise a new one is allocated.
*
* When an object is being deallocated, it is put to CPU-bound magazine.
* If there is no such magazine, new one is allocated (if it fails,
* the object is deallocated into SLAB). If the magazine is full, it is
* put into cpu-shared list of magazines and new one is allocated.
*
* The CPU-bound magazine is actually a pair of magazine to avoid
* thrashing when somebody is allocating/deallocating 1 item at the magazine
* size boundary. LIFO order is enforced, which should avoid fragmentation
* as much as possible.
*
* Every cache contains list of full slabs and list of partialy full slabs.
* Empty SLABS are immediately freed (thrashing will be avoided because
* of magazines).
*
* The SLAB information structure is kept inside the data area, if possible.
* The cache can be marked that it should not use magazines. This is used
* only for SLAB related caches to avoid deadlocks and infinite recursion
* (the SLAB allocator uses itself for allocating all it's control structures).
*
* The SLAB allocator allocates lot of space and does not free it. When
* frame allocator fails to allocate the frame, it calls slab_reclaim().
* It tries 'light reclaim' first, then brutal reclaim. The light reclaim
* releases slabs from cpu-shared magazine-list, until at least 1 slab
* is deallocated in each cache (this algorithm should probably change).
* The brutal reclaim removes all cached objects, even from CPU-bound
* magazines.
*
* TODO: For better CPU-scaling the magazine allocation strategy should
* be extended. Currently, if the cache does not have magazine, it asks
* for non-cpu cached magazine cache to provide one. It might be feasible
* to add cpu-cached magazine cache (which would allocate it's magazines
* from non-cpu-cached mag. cache). This would provide a nice per-cpu
* buffer. The other possibility is to use the per-cache
* 'empty-magazine-list', which decreases competing for 1 per-system
* magazine cache.
*
* - it might be good to add granularity of locks even to slab level,
* we could then try_spinlock over all partial slabs and thus improve
* scalability even on slab level
*/
#include <synch/spinlock.h>
#include <mm/slab.h>
#include <list.h>
#include <memstr.h>
#include <align.h>
#include <mm/heap.h>
#include <mm/frame.h>
#include <config.h>
#include <print.h>
#include <arch.h>
#include <panic.h>
#include <debug.h>
#include <bitops.h>
SPINLOCK_INITIALIZE(slab_cache_lock);
static LIST_INITIALIZE(slab_cache_list);
/** Magazine cache */
static slab_cache_t mag_cache;
/** Cache for cache descriptors */
static slab_cache_t slab_cache_cache;
/** Cache for external slab descriptors
* This time we want per-cpu cache, so do not make it static
* - using SLAB for internal SLAB structures will not deadlock,
* as all slab structures are 'small' - control structures of
* their caches do not require further allocation
*/
static slab_cache_t *slab_extern_cache;
/** Caches for malloc */
static slab_cache_t *malloc_caches[SLAB_MAX_MALLOC_W-SLAB_MIN_MALLOC_W+1];
char *malloc_names[] = {
"malloc-8","malloc-16","malloc-32","malloc-64","malloc-128",
"malloc-256","malloc-512","malloc-1K","malloc-2K",
"malloc-4K","malloc-8K","malloc-16K","malloc-32K",
"malloc-64K","malloc-128K"
};
/** Slab descriptor */
typedef struct {
slab_cache_t *cache; /**< Pointer to parent cache */
link_t link; /* List of full/partial slabs */
void *start; /**< Start address of first available item */
count_t available; /**< Count of available items in this slab */
index_t nextavail; /**< The index of next available item */
}slab_t;
/**************************************/
/* SLAB allocation functions */
/**
* Allocate frames for slab space and initialize
*
*/
static slab_t * slab_space_alloc(slab_cache_t *cache, int flags)
{
void *data;
slab_t *slab;
size_t fsize;
int i;
zone_t *zone = NULL;
int status;
frame_t *frame;
data = (void *)frame_alloc(FRAME_KA | flags, cache->order, &status, &zone);
if (status != FRAME_OK) {
return NULL;
}
if (! (cache->flags & SLAB_CACHE_SLINSIDE)) {
slab = slab_alloc(slab_extern_cache, flags);
if (!slab) {
frame_free((__address)data);
return NULL;
}
} else {
fsize = (PAGE_SIZE << cache->order);
slab = data + fsize - sizeof(*slab);
}
/* Fill in slab structures */
/* TODO: some better way of accessing the frame */
for (i=0; i < (1 << cache->order); i++) {
frame = ADDR2FRAME(zone, KA2PA((__address)(data+i*PAGE_SIZE)));
frame->parent = slab;
}
slab->start = data;
slab->available = cache->objects;
slab->nextavail = 0;
slab->cache = cache;
for (i=0; i<cache->objects;i++)
*((int *) (slab->start + i*cache->size)) = i+1;
atomic_inc(&cache->allocated_slabs);
return slab;
}
/**
* Deallocate space associated with SLAB
*
* @return number of freed frames
*/
static count_t slab_space_free(slab_cache_t *cache, slab_t *slab)
{
frame_free((__address)slab->start);
if (! (cache->flags & SLAB_CACHE_SLINSIDE))
slab_free(slab_extern_cache, slab);
atomic_dec(&cache->allocated_slabs);
return 1 << cache->order;
}
/** Map object to slab structure */
static slab_t * obj2slab(void *obj)
{
frame_t *frame;
frame = frame_addr2frame((__address)obj);
return (slab_t *)frame->parent;
}
/**************************************/
/* SLAB functions */
/**
* Return object to slab and call a destructor
*
* @param slab If the caller knows directly slab of the object, otherwise NULL
*
* @return Number of freed pages
*/
static count_t slab_obj_destroy(slab_cache_t *cache, void *obj,
slab_t *slab)
{
if (!slab)
slab = obj2slab(obj);
ASSERT(slab->cache == cache);
ASSERT(slab->available < cache->objects);
spinlock_lock(&cache->slablock);
*((int *)obj) = slab->nextavail;
slab->nextavail = (obj - slab->start)/cache->size;
slab->available++;
/* Move it to correct list */
if (slab->available == cache->objects) {
/* Free associated memory */
list_remove(&slab->link);
spinlock_unlock(&cache->slablock);
return slab_space_free(cache, slab);
} else if (slab->available == 1) {
/* It was in full, move to partial */
list_remove(&slab->link);
list_prepend(&slab->link, &cache->partial_slabs);
spinlock_unlock(&cache->slablock);
}
return 0;
}
/**
* Take new object from slab or create new if needed
*
* @return Object address or null
*/
static void * slab_obj_create(slab_cache_t *cache, int flags)
{
slab_t *slab;
void *obj;
spinlock_lock(&cache->slablock);
if (list_empty(&cache->partial_slabs)) {
/* Allow recursion and reclaiming
* - this should work, as the SLAB control structures
* are small and do not need to allocte with anything
* other ten frame_alloc when they are allocating,
* that's why we should get recursion at most 1-level deep
*/
spinlock_unlock(&cache->slablock);
slab = slab_space_alloc(cache, flags);
if (!slab)
return NULL;
spinlock_lock(&cache->slablock);
} else {
slab = list_get_instance(cache->partial_slabs.next,
slab_t,
link);
list_remove(&slab->link);
}
obj = slab->start + slab->nextavail * cache->size;
slab->nextavail = *((int *)obj);
slab->available--;
if (! slab->available)
list_prepend(&slab->link, &cache->full_slabs);
else
list_prepend(&slab->link, &cache->partial_slabs);
spinlock_unlock(&cache->slablock);
return obj;
}
/**************************************/
/* CPU-Cache slab functions */
/**
* Finds a full magazine in cache, takes it from list
* and returns it
*
* @param first If true, return first, else last mag
*/
static slab_magazine_t * get_mag_from_cache(slab_cache_t *cache,
int first)
{
slab_magazine_t *mag = NULL;
link_t *cur;
spinlock_lock(&cache->maglock);
if (!list_empty(&cache->magazines)) {
if (first)
cur = cache->magazines.next;
else
cur = cache->magazines.prev;
mag = list_get_instance(cur, slab_magazine_t, link);
list_remove(&mag->link);
atomic_dec(&cache->magazine_counter);
}
spinlock_unlock(&cache->maglock);
return mag;
}
/** Prepend magazine to magazine list in cache */
static void put_mag_to_cache(slab_cache_t *cache, slab_magazine_t *mag)
{
spinlock_lock(&cache->maglock);
list_prepend(&mag->link, &cache->magazines);
atomic_inc(&cache->magazine_counter);
spinlock_unlock(&cache->maglock);
}
/**
* Free all objects in magazine and free memory associated with magazine
*
* @return Number of freed pages
*/
static count_t magazine_destroy(slab_cache_t *cache,
slab_magazine_t *mag)
{
int i;
count_t frames = 0;
for (i=0;i < mag->busy; i++) {
frames += slab_obj_destroy(cache, mag->objs[i], NULL);
atomic_dec(&cache->cached_objs);
}
slab_free(&mag_cache, mag);
return frames;
}
/**
* Find full magazine, set it as current and return it
*
* Assume cpu_magazine lock is held
*/
static slab_magazine_t * get_full_current_mag(slab_cache_t *cache)
{
slab_magazine_t *cmag, *lastmag, *newmag;
cmag = cache->mag_cache[CPU->id].current;
lastmag = cache->mag_cache[CPU->id].last;
if (cmag) { /* First try local CPU magazines */
if (cmag->busy)
return cmag;
if (lastmag && lastmag->busy) {
cache->mag_cache[CPU->id].current = lastmag;
cache->mag_cache[CPU->id].last = cmag;
return lastmag;
}
}
/* Local magazines are empty, import one from magazine list */
newmag = get_mag_from_cache(cache, 1);
if (!newmag)
return NULL;
if (lastmag)
magazine_destroy(cache, lastmag);
cache->mag_cache[CPU->id].last = cmag;
cache->mag_cache[CPU->id].current = newmag;
return newmag;
}
/**
* Try to find object in CPU-cache magazines
*
* @return Pointer to object or NULL if not available
*/
static void * magazine_obj_get(slab_cache_t *cache)
{
slab_magazine_t *mag;
void *obj;
if (!CPU)
return NULL;
spinlock_lock(&cache->mag_cache[CPU->id].lock);
mag = get_full_current_mag(cache);
if (!mag) {
spinlock_unlock(&cache->mag_cache[CPU->id].lock);
return NULL;
}
obj = mag->objs[--mag->busy];
spinlock_unlock(&cache->mag_cache[CPU->id].lock);
atomic_dec(&cache->cached_objs);
return obj;
}
/**
* Assure that the current magazine is empty, return pointer to it, or NULL if
* no empty magazine is available and cannot be allocated
*
* Assume mag_cache[CPU->id].lock is held
*
* We have 2 magazines bound to processor.
* First try the current.
* If full, try the last.
* If full, put to magazines list.
* allocate new, exchange last & current
*
*/
static slab_magazine_t * make_empty_current_mag(slab_cache_t *cache)
{
slab_magazine_t *cmag,*lastmag,*newmag;
cmag = cache->mag_cache[CPU->id].current;
lastmag = cache->mag_cache[CPU->id].last;
if (cmag) {
if (cmag->busy < cmag->size)
return cmag;
if (lastmag && lastmag->busy < lastmag->size) {
cache->mag_cache[CPU->id].last = cmag;
cache->mag_cache[CPU->id].current = lastmag;
return lastmag;
}
}
/* current | last are full | nonexistent, allocate new */
/* We do not want to sleep just because of caching */
/* Especially we do not want reclaiming to start, as
* this would deadlock */
newmag = slab_alloc(&mag_cache, FRAME_ATOMIC | FRAME_NO_RECLAIM);
if (!newmag)
return NULL;
newmag->size = SLAB_MAG_SIZE;
newmag->busy = 0;
/* Flush last to magazine list */
if (lastmag)
put_mag_to_cache(cache, lastmag);
/* Move current as last, save new as current */
cache->mag_cache[CPU->id].last = cmag;
cache->mag_cache[CPU->id].current = newmag;
return newmag;
}
/**
* Put object into CPU-cache magazine
*
* @return 0 - success, -1 - could not get memory
*/
static int magazine_obj_put(slab_cache_t *cache, void *obj)
{
slab_magazine_t *mag;
if (!CPU)
return -1;
spinlock_lock(&cache->mag_cache[CPU->id].lock);
mag = make_empty_current_mag(cache);
if (!mag) {
spinlock_unlock(&cache->mag_cache[CPU->id].lock);
return -1;
}
mag->objs[mag->busy++] = obj;
spinlock_unlock(&cache->mag_cache[CPU->id].lock);
atomic_inc(&cache->cached_objs);
return 0;
}
/**************************************/
/* SLAB CACHE functions */
/** Return number of objects that fit in certain cache size */
static int comp_objects(slab_cache_t *cache)
{
if (cache->flags & SLAB_CACHE_SLINSIDE)
return ((PAGE_SIZE << cache->order) - sizeof(slab_t)) / cache->size;
else
return (PAGE_SIZE << cache->order) / cache->size;
}
/** Return wasted space in slab */
static int badness(slab_cache_t *cache)
{
int objects;
int ssize;
objects = comp_objects(cache);
ssize = PAGE_SIZE << cache->order;
if (cache->flags & SLAB_CACHE_SLINSIDE)
ssize -= sizeof(slab_t);
return ssize - objects*cache->size;
}
/** Initialize allocated memory as a slab cache */
static void
_slab_cache_create(slab_cache_t *cache,
char *name,
size_t size,
size_t align,
int (*constructor)(void *obj, int kmflag),
void (*destructor)(void *obj),
int flags)
{
int i;
int pages;
memsetb((__address)cache, sizeof(*cache), 0);
cache->name = name;
if (align < sizeof(__native))
align = sizeof(__native);
size = ALIGN_UP(size, align);
cache->size = size;
cache->constructor = constructor;
cache->destructor = destructor;
cache->flags = flags;
list_initialize(&cache->full_slabs);
list_initialize(&cache->partial_slabs);
list_initialize(&cache->magazines);
spinlock_initialize(&cache->slablock, "slab_lock");
spinlock_initialize(&cache->maglock, "slab_maglock");
if (! (cache->flags & SLAB_CACHE_NOMAGAZINE)) {
for (i=0; i < config.cpu_count; i++) {
memsetb((__address)&cache->mag_cache[i],
sizeof(cache->mag_cache[i]), 0);
spinlock_initialize(&cache->mag_cache[i].lock,
"slab_maglock_cpu");
}
}
/* Compute slab sizes, object counts in slabs etc. */
if (cache->size < SLAB_INSIDE_SIZE)
cache->flags |= SLAB_CACHE_SLINSIDE;
/* Minimum slab order */
pages = ((cache->size-1) >> PAGE_WIDTH) + 1;
cache->order = fnzb(pages);
while (badness(cache) > SLAB_MAX_BADNESS(cache)) {
cache->order += 1;
}
cache->objects = comp_objects(cache);
/* If info fits in, put it inside */
if (badness(cache) > sizeof(slab_t))
cache->flags |= SLAB_CACHE_SLINSIDE;
spinlock_lock(&slab_cache_lock);
list_append(&cache->link, &slab_cache_list);
spinlock_unlock(&slab_cache_lock);
}
/** Create slab cache */
slab_cache_t * slab_cache_create(char *name,
size_t size,
size_t align,
int (*constructor)(void *obj, int kmflag),
void (*destructor)(void *obj),
int flags)
{
slab_cache_t *cache;
cache = slab_alloc(&slab_cache_cache, 0);
_slab_cache_create(cache, name, size, align, constructor, destructor,
flags);
return cache;
}
/**
* Reclaim space occupied by objects that are already free
*
* @param flags If contains SLAB_RECLAIM_ALL, do aggressive freeing
* @return Number of freed pages
*/
static count_t _slab_reclaim(slab_cache_t *cache, int flags)
{
int i;
slab_magazine_t *mag;
count_t frames = 0;
int magcount;
if (cache->flags & SLAB_CACHE_NOMAGAZINE)
return 0; /* Nothing to do */
/* We count up to original magazine count to avoid
* endless loop
*/
magcount = atomic_get(&cache->magazine_counter);
while (magcount-- && (mag=get_mag_from_cache(cache,0))) {
frames += magazine_destroy(cache,mag);
if (!(flags & SLAB_RECLAIM_ALL) && frames)
break;
}
if (flags & SLAB_RECLAIM_ALL) {
/* Free cpu-bound magazines */
/* Destroy CPU magazines */
for (i=0; i<config.cpu_count; i++) {
spinlock_lock(&cache->mag_cache[i].lock);
mag = cache->mag_cache[i].current;
if (mag)
frames += magazine_destroy(cache, mag);
cache->mag_cache[i].current = NULL;
mag = cache->mag_cache[i].last;
if (mag)
frames += magazine_destroy(cache, mag);
cache->mag_cache[i].last = NULL;
spinlock_unlock(&cache->mag_cache[i].lock);
}
}
return frames;
}
/** Check that there are no slabs and remove cache from system */
void slab_cache_destroy(slab_cache_t *cache)
{
ipl_t ipl;
/* First remove cache from link, so that we don't need
* to disable interrupts later
*/
ipl = interrupts_disable();
spinlock_lock(&slab_cache_lock);
list_remove(&cache->link);
spinlock_unlock(&slab_cache_lock);
interrupts_restore(ipl);
/* Do not lock anything, we assume the software is correct and
* does not touch the cache when it decides to destroy it */
/* Destroy all magazines */
_slab_reclaim(cache, SLAB_RECLAIM_ALL);
/* All slabs must be empty */
if (!list_empty(&cache->full_slabs) \
|| !list_empty(&cache->partial_slabs))
panic("Destroying cache that is not empty.");
slab_free(&slab_cache_cache, cache);
}
/** Allocate new object from cache - if no flags given, always returns
memory */
void * slab_alloc(slab_cache_t *cache, int flags)
{
ipl_t ipl;
void *result = NULL;
/* Disable interrupts to avoid deadlocks with interrupt handlers */
ipl = interrupts_disable();
if (!(cache->flags & SLAB_CACHE_NOMAGAZINE))
result = magazine_obj_get(cache);
if (!result)
result = slab_obj_create(cache, flags);
interrupts_restore(ipl);
if (result)
atomic_inc(&cache->allocated_objs);
return result;
}
/** Return object to cache, use slab if known */
static void _slab_free(slab_cache_t *cache, void *obj, slab_t *slab)
{
ipl_t ipl;
ipl = interrupts_disable();
if ((cache->flags & SLAB_CACHE_NOMAGAZINE) \
|| magazine_obj_put(cache, obj)) {
slab_obj_destroy(cache, obj, slab);
}
interrupts_restore(ipl);
atomic_dec(&cache->allocated_objs);
}
/** Return slab object to cache */
void slab_free(slab_cache_t *cache, void *obj)
{
_slab_free(cache,obj,NULL);
}
/* Go through all caches and reclaim what is possible */
count_t slab_reclaim(int flags)
{
slab_cache_t *cache;
link_t *cur;
count_t frames = 0;
spinlock_lock(&slab_cache_lock);
/* TODO: Add assert, that interrupts are disabled, otherwise
* memory allocation from interrupts can deadlock.
*/
for (cur = slab_cache_list.next;cur!=&slab_cache_list; cur=cur->next) {
cache = list_get_instance(cur, slab_cache_t, link);
frames += _slab_reclaim(cache, flags);
}
spinlock_unlock(&slab_cache_lock);
return frames;
}
/* Print list of slabs */
void slab_print_list(void)
{
slab_cache_t *cache;
link_t *cur;
spinlock_lock(&slab_cache_lock);
printf("SLAB name\tOsize\tPages\tObj/pg\tSlabs\tCached\tAllocobjs\tCtl\n"); for (cur = slab_cache_list.next;cur!=&slab_cache_list; cur=cur->next) {
cache = list_get_instance(cur, slab_cache_t, link);
printf("%s\t%d\t%d\t%d\t%d\t%d\t%d\t\t%s\n", cache
->name
, cache
->size
, (1 << cache->order), cache->objects,
atomic_get(&cache->allocated_slabs),
atomic_get(&cache->cached_objs),
atomic_get(&cache->allocated_objs),
cache->flags & SLAB_CACHE_SLINSIDE ? "In" : "Out");
}
spinlock_unlock(&slab_cache_lock);
}
#ifdef CONFIG_DEBUG
static int _slab_initialized = 0;
#endif
void slab_cache_init(void)
{
int i, size;
/* Initialize magazine cache */
_slab_cache_create(&mag_cache,
"slab_magazine",
sizeof(slab_magazine_t)+SLAB_MAG_SIZE*sizeof(void*),
sizeof(__address),
NULL, NULL,
SLAB_CACHE_NOMAGAZINE | SLAB_CACHE_SLINSIDE);
/* Initialize slab_cache cache */
_slab_cache_create(&slab_cache_cache,
"slab_cache",
sizeof(slab_cache_cache) + config.cpu_count*sizeof(slab_cache_cache.mag_cache[0]),
sizeof(__address),
NULL, NULL,
SLAB_CACHE_NOMAGAZINE | SLAB_CACHE_SLINSIDE);
/* Initialize external slab cache */
slab_extern_cache = slab_cache_create("slab_extern",
sizeof(slab_t),
0, NULL, NULL,
SLAB_CACHE_SLINSIDE);
/* Initialize structures for malloc */
for (i=0, size=(1<<SLAB_MIN_MALLOC_W);
i < (SLAB_MAX_MALLOC_W-SLAB_MIN_MALLOC_W+1);
i++, size <<= 1) {
malloc_caches[i] = slab_cache_create(malloc_names[i],
size, 0,
NULL,NULL,0);
}
#ifdef CONFIG_DEBUG
_slab_initialized = 1;
#endif
}
/**************************************/
/* kalloc/kfree functions */
void * kalloc(unsigned int size, int flags)
{
int idx;
ASSERT(_slab_initialized);
ASSERT( size && size <= (1 << SLAB_MAX_MALLOC_W));
if (size < (1 << SLAB_MIN_MALLOC_W))
size = (1 << SLAB_MIN_MALLOC_W);
idx = fnzb(size-1) - SLAB_MIN_MALLOC_W + 1;
return slab_alloc(malloc_caches[idx], flags);
}
void kfree(void *obj)
{
slab_t *slab;
if (!obj) return;
slab = obj2slab(obj);
_slab_free(slab->cache, obj, slab);
}