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Slab allocators: Drop support for destructors
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There is no user of destructors left.  There is no reason why we should keep
checking for destructors calls in the slab allocators.

The RFC for this patch was discussed at
http://marc.info/?l=linux-kernel&m=117882364330705&w=2

Destructors were mainly used for list management which required them to take a
spinlock.  Taking a spinlock in a destructor is a bit risky since the slab
allocators may run the destructors anytime they decide a slab is no longer
needed.

Patch drops destructor support.  Any attempt to use a destructor will BUG().

Acked-by: Pekka Enberg <[email protected]>
Acked-by: Paul Mundt <[email protected]>
Signed-off-by: Christoph Lameter <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
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Christoph Lameter authored and Linus Torvalds committed May 17, 2007
1 parent afc0ced commit c59def9
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Showing 4 changed files with 16 additions and 62 deletions.
1 change: 0 additions & 1 deletion include/linux/slub_def.h
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Original file line number Diff line number Diff line change
Expand Up @@ -40,7 +40,6 @@ struct kmem_cache {
int objects; /* Number of objects in slab */
int refcount; /* Refcount for slab cache destroy */
void (*ctor)(void *, struct kmem_cache *, unsigned long);
void (*dtor)(void *, struct kmem_cache *, unsigned long);
int inuse; /* Offset to metadata */
int align; /* Alignment */
const char *name; /* Name (only for display!) */
Expand Down
27 changes: 2 additions & 25 deletions mm/slab.c
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Original file line number Diff line number Diff line change
Expand Up @@ -409,9 +409,6 @@ struct kmem_cache {
/* constructor func */
void (*ctor) (void *, struct kmem_cache *, unsigned long);

/* de-constructor func */
void (*dtor) (void *, struct kmem_cache *, unsigned long);

/* 5) cache creation/removal */
const char *name;
struct list_head next;
Expand Down Expand Up @@ -1911,20 +1908,11 @@ static void slab_destroy_objs(struct kmem_cache *cachep, struct slab *slabp)
slab_error(cachep, "end of a freed object "
"was overwritten");
}
if (cachep->dtor && !(cachep->flags & SLAB_POISON))
(cachep->dtor) (objp + obj_offset(cachep), cachep, 0);
}
}
#else
static void slab_destroy_objs(struct kmem_cache *cachep, struct slab *slabp)
{
if (cachep->dtor) {
int i;
for (i = 0; i < cachep->num; i++) {
void *objp = index_to_obj(cachep, slabp, i);
(cachep->dtor) (objp, cachep, 0);
}
}
}
#endif

Expand Down Expand Up @@ -2124,7 +2112,7 @@ static int setup_cpu_cache(struct kmem_cache *cachep)
* @align: The required alignment for the objects.
* @flags: SLAB flags
* @ctor: A constructor for the objects.
* @dtor: A destructor for the objects.
* @dtor: A destructor for the objects (not implemented anymore).
*
* Returns a ptr to the cache on success, NULL on failure.
* Cannot be called within a int, but can be interrupted.
Expand Down Expand Up @@ -2159,7 +2147,7 @@ kmem_cache_create (const char *name, size_t size, size_t align,
* Sanity checks... these are all serious usage bugs.
*/
if (!name || in_interrupt() || (size < BYTES_PER_WORD) ||
(size > (1 << MAX_OBJ_ORDER) * PAGE_SIZE) || (dtor && !ctor)) {
(size > (1 << MAX_OBJ_ORDER) * PAGE_SIZE) || dtor) {
printk(KERN_ERR "%s: Early error in slab %s\n", __FUNCTION__,
name);
BUG();
Expand Down Expand Up @@ -2213,9 +2201,6 @@ kmem_cache_create (const char *name, size_t size, size_t align,
if (flags & SLAB_DESTROY_BY_RCU)
BUG_ON(flags & SLAB_POISON);
#endif
if (flags & SLAB_DESTROY_BY_RCU)
BUG_ON(dtor);

/*
* Always checks flags, a caller might be expecting debug support which
* isn't available.
Expand Down Expand Up @@ -2370,7 +2355,6 @@ kmem_cache_create (const char *name, size_t size, size_t align,
BUG_ON(!cachep->slabp_cache);
}
cachep->ctor = ctor;
cachep->dtor = dtor;
cachep->name = name;

if (setup_cpu_cache(cachep)) {
Expand Down Expand Up @@ -2835,7 +2819,6 @@ static int cache_grow(struct kmem_cache *cachep,
* Perform extra freeing checks:
* - detect bad pointers.
* - POISON/RED_ZONE checking
* - destructor calls, for caches with POISON+dtor
*/
static void kfree_debugcheck(const void *objp)
{
Expand Down Expand Up @@ -2894,12 +2877,6 @@ static void *cache_free_debugcheck(struct kmem_cache *cachep, void *objp,
BUG_ON(objnr >= cachep->num);
BUG_ON(objp != index_to_obj(cachep, slabp, objnr));

if (cachep->flags & SLAB_POISON && cachep->dtor) {
/* we want to cache poison the object,
* call the destruction callback
*/
cachep->dtor(objp + obj_offset(cachep), cachep, 0);
}
#ifdef CONFIG_DEBUG_SLAB_LEAK
slab_bufctl(slabp)[objnr] = BUFCTL_FREE;
#endif
Expand Down
5 changes: 0 additions & 5 deletions mm/slob.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -280,7 +280,6 @@ struct kmem_cache {
unsigned long flags;
const char *name;
void (*ctor)(void *, struct kmem_cache *, unsigned long);
void (*dtor)(void *, struct kmem_cache *, unsigned long);
};

struct kmem_cache *kmem_cache_create(const char *name, size_t size,
Expand All @@ -296,13 +295,11 @@ struct kmem_cache *kmem_cache_create(const char *name, size_t size,
c->name = name;
c->size = size;
if (flags & SLAB_DESTROY_BY_RCU) {
BUG_ON(dtor);
/* leave room for rcu footer at the end of object */
c->size += sizeof(struct slob_rcu);
}
c->flags = flags;
c->ctor = ctor;
c->dtor = dtor;
/* ignore alignment unless it's forced */
c->align = (flags & SLAB_HWCACHE_ALIGN) ? SLOB_ALIGN : 0;
if (c->align < align)
Expand Down Expand Up @@ -371,8 +368,6 @@ void kmem_cache_free(struct kmem_cache *c, void *b)
slob_rcu->size = c->size;
call_rcu(&slob_rcu->head, kmem_rcu_free);
} else {
if (c->dtor)
c->dtor(b, c, 0);
__kmem_cache_free(b, c->size);
}
}
Expand Down
45 changes: 14 additions & 31 deletions mm/slub.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -891,13 +891,13 @@ static void kmem_cache_open_debug_check(struct kmem_cache *s)
* On 32 bit platforms the limit is 256k. On 64bit platforms
* the limit is 512k.
*
* Debugging or ctor/dtors may create a need to move the free
* Debugging or ctor may create a need to move the free
* pointer. Fail if this happens.
*/
if (s->size >= 65535 * sizeof(void *)) {
BUG_ON(s->flags & (SLAB_RED_ZONE | SLAB_POISON |
SLAB_STORE_USER | SLAB_DESTROY_BY_RCU));
BUG_ON(s->ctor || s->dtor);
BUG_ON(s->ctor);
}
else
/*
Expand Down Expand Up @@ -1030,15 +1030,12 @@ static void __free_slab(struct kmem_cache *s, struct page *page)
{
int pages = 1 << s->order;

if (unlikely(SlabDebug(page) || s->dtor)) {
if (unlikely(SlabDebug(page))) {
void *p;

slab_pad_check(s, page);
for_each_object(p, s, page_address(page)) {
if (s->dtor)
s->dtor(p, s, 0);
for_each_object(p, s, page_address(page))
check_object(s, page, p, 0);
}
}

mod_zone_page_state(page_zone(page),
Expand Down Expand Up @@ -1871,7 +1868,7 @@ static int calculate_sizes(struct kmem_cache *s)
* then we should never poison the object itself.
*/
if ((flags & SLAB_POISON) && !(flags & SLAB_DESTROY_BY_RCU) &&
!s->ctor && !s->dtor)
!s->ctor)
s->flags |= __OBJECT_POISON;
else
s->flags &= ~__OBJECT_POISON;
Expand Down Expand Up @@ -1901,7 +1898,7 @@ static int calculate_sizes(struct kmem_cache *s)

#ifdef CONFIG_SLUB_DEBUG
if (((flags & (SLAB_DESTROY_BY_RCU | SLAB_POISON)) ||
s->ctor || s->dtor)) {
s->ctor)) {
/*
* Relocate free pointer after the object if it is not
* permitted to overwrite the first word of the object on
Expand Down Expand Up @@ -1970,13 +1967,11 @@ static int calculate_sizes(struct kmem_cache *s)
static int kmem_cache_open(struct kmem_cache *s, gfp_t gfpflags,
const char *name, size_t size,
size_t align, unsigned long flags,
void (*ctor)(void *, struct kmem_cache *, unsigned long),
void (*dtor)(void *, struct kmem_cache *, unsigned long))
void (*ctor)(void *, struct kmem_cache *, unsigned long))
{
memset(s, 0, kmem_size);
s->name = name;
s->ctor = ctor;
s->dtor = dtor;
s->objsize = size;
s->flags = flags;
s->align = align;
Expand Down Expand Up @@ -2161,7 +2156,7 @@ static struct kmem_cache *create_kmalloc_cache(struct kmem_cache *s,

down_write(&slub_lock);
if (!kmem_cache_open(s, gfp_flags, name, size, ARCH_KMALLOC_MINALIGN,
flags, NULL, NULL))
flags, NULL))
goto panic;

list_add(&s->list, &slab_caches);
Expand Down Expand Up @@ -2463,23 +2458,22 @@ static int slab_unmergeable(struct kmem_cache *s)
if (slub_nomerge || (s->flags & SLUB_NEVER_MERGE))
return 1;

if (s->ctor || s->dtor)
if (s->ctor)
return 1;

return 0;
}

static struct kmem_cache *find_mergeable(size_t size,
size_t align, unsigned long flags,
void (*ctor)(void *, struct kmem_cache *, unsigned long),
void (*dtor)(void *, struct kmem_cache *, unsigned long))
void (*ctor)(void *, struct kmem_cache *, unsigned long))
{
struct list_head *h;

if (slub_nomerge || (flags & SLUB_NEVER_MERGE))
return NULL;

if (ctor || dtor)
if (ctor)
return NULL;

size = ALIGN(size, sizeof(void *));
Expand Down Expand Up @@ -2521,8 +2515,9 @@ struct kmem_cache *kmem_cache_create(const char *name, size_t size,
{
struct kmem_cache *s;

BUG_ON(dtor);
down_write(&slub_lock);
s = find_mergeable(size, align, flags, ctor, dtor);
s = find_mergeable(size, align, flags, ctor);
if (s) {
s->refcount++;
/*
Expand All @@ -2536,7 +2531,7 @@ struct kmem_cache *kmem_cache_create(const char *name, size_t size,
} else {
s = kmalloc(kmem_size, GFP_KERNEL);
if (s && kmem_cache_open(s, GFP_KERNEL, name,
size, align, flags, ctor, dtor)) {
size, align, flags, ctor)) {
if (sysfs_slab_add(s)) {
kfree(s);
goto err;
Expand Down Expand Up @@ -3177,17 +3172,6 @@ static ssize_t ctor_show(struct kmem_cache *s, char *buf)
}
SLAB_ATTR_RO(ctor);

static ssize_t dtor_show(struct kmem_cache *s, char *buf)
{
if (s->dtor) {
int n = sprint_symbol(buf, (unsigned long)s->dtor);

return n + sprintf(buf + n, "\n");
}
return 0;
}
SLAB_ATTR_RO(dtor);

static ssize_t aliases_show(struct kmem_cache *s, char *buf)
{
return sprintf(buf, "%d\n", s->refcount - 1);
Expand Down Expand Up @@ -3419,7 +3403,6 @@ static struct attribute * slab_attrs[] = {
&partial_attr.attr,
&cpu_slabs_attr.attr,
&ctor_attr.attr,
&dtor_attr.attr,
&aliases_attr.attr,
&align_attr.attr,
&sanity_checks_attr.attr,
Expand Down

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