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mm/slab: abstract slabobj_ext access via new slab_obj_ext() helper

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Currently, the slab allocator assumes that slab->obj_exts is a pointer
to an array of struct slabobj_ext objects. However, to support storage
methods where struct slabobj_ext is embedded within objects, the slab
allocator should not make this assumption. Instead of directly
dereferencing the slabobj_exts array, abstract access to
struct slabobj_ext via helper functions.

Introduce a new API slabobj_ext metadata access:

  slab_obj_ext(slab, obj_exts, index) - returns the pointer to
  struct slabobj_ext element at the given index.

Directly dereferencing the return value of slab_obj_exts() is no longer
allowed. Instead, slab_obj_ext() must always be used to access
individual struct slabobj_ext objects.

Convert all users to use these APIs.
No functional changes intended.

Signed-off-by: Harry Yoo <harry.yoo@oracle.com>
Link: https://patch.msgid.link/20260113061845.159790-5-harry.yoo@oracle.com
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
This commit is contained in:
Harry Yoo 2026-01-13 15:18:40 +09:00 • committed by Vlastimil Babka
parent 43d9bb4236
commit 52f1ca8a45
3 changed files with 79 additions and 32 deletions
Download patch file Download diff file Expand all files Collapse all files

23
mm/memcontrol.c
View file

@ -2596,7 +2596,8 @@ struct mem_cgroup *mem_cgroup_from_obj_slab(struct slab *slab, void *p)
* Memcg membership data for each individual object is saved in
* slab->obj_exts.
*/
struct slabobj_ext *obj_exts;
unsigned long obj_exts;
struct slabobj_ext *obj_ext;
unsigned int off;
obj_exts = slab_obj_exts(slab);
@ -2604,8 +2605,9 @@ struct mem_cgroup *mem_cgroup_from_obj_slab(struct slab *slab, void *p)
return NULL;
off = obj_to_index(slab->slab_cache, slab, p);
if (obj_exts[off].objcg)
return obj_cgroup_memcg(obj_exts[off].objcg);
obj_ext = slab_obj_ext(slab, obj_exts, off);
if (obj_ext->objcg)
return obj_cgroup_memcg(obj_ext->objcg);
return NULL;
}
@ -3191,6 +3193,9 @@ bool __memcg_slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *lru,
}
for (i = 0; i < size; i++) {
unsigned long obj_exts;
struct slabobj_ext *obj_ext;
slab = virt_to_slab(p[i]);
if (!slab_obj_exts(slab) &&
@ -3213,29 +3218,33 @@ bool __memcg_slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *lru,
slab_pgdat(slab), cache_vmstat_idx(s)))
return false;
obj_exts = slab_obj_exts(slab);
off = obj_to_index(s, slab, p[i]);
obj_ext = slab_obj_ext(slab, obj_exts, off);
obj_cgroup_get(objcg);
slab_obj_exts(slab)[off].objcg = objcg;
obj_ext->objcg = objcg;
}
return true;
}
void __memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab,
void **p, int objects, struct slabobj_ext *obj_exts)
void **p, int objects, unsigned long obj_exts)
{
size_t obj_size = obj_full_size(s);
for (int i = 0; i < objects; i++) {
struct obj_cgroup *objcg;
struct slabobj_ext *obj_ext;
unsigned int off;
off = obj_to_index(s, slab, p[i]);
objcg = obj_exts[off].objcg;
obj_ext = slab_obj_ext(slab, obj_exts, off);
objcg = obj_ext->objcg;
if (!objcg)
continue;
obj_exts[off].objcg = NULL;
obj_ext->objcg = NULL;
refill_obj_stock(objcg, obj_size, true, -obj_size,
slab_pgdat(slab), cache_vmstat_idx(s));
obj_cgroup_put(objcg);

43
mm/slab.h
View file

@ -507,10 +507,12 @@ static inline bool slab_in_kunit_test(void) { return false; }
* associated with a slab.
* @slab: a pointer to the slab struct
*
* Returns a pointer to the object extension vector associated with the slab,
* or NULL if no such vector has been associated yet.
* Returns the address of the object extension vector associated with the slab,
* or zero if no such vector has been associated yet.
* Do not dereference the return value directly; use slab_obj_ext() to access
* its elements.
*/
static inline struct slabobj_ext *slab_obj_exts(struct slab *slab)
static inline unsigned long slab_obj_exts(struct slab *slab)
{
unsigned long obj_exts = READ_ONCE(slab->obj_exts);
@ -523,7 +525,29 @@ static inline struct slabobj_ext *slab_obj_exts(struct slab *slab)
obj_exts != OBJEXTS_ALLOC_FAIL, slab_page(slab));
VM_BUG_ON_PAGE(obj_exts & MEMCG_DATA_KMEM, slab_page(slab));
#endif
return (struct slabobj_ext *)(obj_exts & ~OBJEXTS_FLAGS_MASK);
return obj_exts & ~OBJEXTS_FLAGS_MASK;
}
/*
* slab_obj_ext - get the pointer to the slab object extension metadata
* associated with an object in a slab.
* @slab: a pointer to the slab struct
* @obj_exts: a pointer to the object extension vector
* @index: an index of the object
*
* Returns a pointer to the object extension associated with the object.
*/
static inline struct slabobj_ext *slab_obj_ext(struct slab *slab,
unsigned long obj_exts,
unsigned int index)
{
struct slabobj_ext *obj_ext;
VM_WARN_ON_ONCE(obj_exts != slab_obj_exts(slab));
obj_ext = (struct slabobj_ext *)obj_exts;
return &obj_ext[index];
}
int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,
@ -531,7 +555,14 @@ int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,
#else /* CONFIG_SLAB_OBJ_EXT */
static inline struct slabobj_ext *slab_obj_exts(struct slab *slab)
static inline unsigned long slab_obj_exts(struct slab *slab)
{
return 0;
}
static inline struct slabobj_ext *slab_obj_ext(struct slab *slab,
unsigned long obj_exts,
unsigned int index)
{
return NULL;
}
@ -548,7 +579,7 @@ static inline enum node_stat_item cache_vmstat_idx(struct kmem_cache *s)
bool __memcg_slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *lru,
gfp_t flags, size_t size, void **p);
void __memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab,
void **p, int objects, struct slabobj_ext *obj_exts);
void **p, int objects, unsigned long obj_exts);
#endif
void kvfree_rcu_cb(struct rcu_head *head);

45
mm/slub.c
View file

@ -2055,7 +2055,7 @@ static bool freelist_corrupted(struct kmem_cache *s, struct slab *slab,
static inline void mark_objexts_empty(struct slabobj_ext *obj_exts)
{
struct slabobj_ext *slab_exts;
unsigned long slab_exts;
struct slab *obj_exts_slab;
obj_exts_slab = virt_to_slab(obj_exts);
@ -2063,13 +2063,15 @@ static inline void mark_objexts_empty(struct slabobj_ext *obj_exts)
if (slab_exts) {
unsigned int offs = obj_to_index(obj_exts_slab->slab_cache,
obj_exts_slab, obj_exts);
struct slabobj_ext *ext = slab_obj_ext(obj_exts_slab,
slab_exts, offs);
if (unlikely(is_codetag_empty(&slab_exts[offs].ref)))
if (unlikely(is_codetag_empty(&ext->ref)))
return;
/* codetag should be NULL here */
WARN_ON(slab_exts[offs].ref.ct);
set_codetag_empty(&slab_exts[offs].ref);
WARN_ON(ext->ref.ct);
set_codetag_empty(&ext->ref);
}
}
@ -2237,7 +2239,7 @@ static inline void free_slab_obj_exts(struct slab *slab)
{
struct slabobj_ext *obj_exts;
obj_exts = slab_obj_exts(slab);
obj_exts = (struct slabobj_ext *)slab_obj_exts(slab);
if (!obj_exts) {
/*
* If obj_exts allocation failed, slab->obj_exts is set to
@ -2284,26 +2286,29 @@ static inline void free_slab_obj_exts(struct slab *slab)
#ifdef CONFIG_MEM_ALLOC_PROFILING
static inline struct slabobj_ext *
prepare_slab_obj_exts_hook(struct kmem_cache *s, gfp_t flags, void *p)
prepare_slab_obj_ext_hook(struct kmem_cache *s, gfp_t flags, void *p)
{
struct slab *slab;
unsigned long obj_exts;
slab = virt_to_slab(p);
if (!slab_obj_exts(slab) &&
obj_exts = slab_obj_exts(slab);
if (!obj_exts &&
alloc_slab_obj_exts(slab, s, flags, false)) {
pr_warn_once("%s, %s: Failed to create slab extension vector!\n",
__func__, s->name);
return NULL;
}
return slab_obj_exts(slab) + obj_to_index(s, slab, p);
obj_exts = slab_obj_exts(slab);
return slab_obj_ext(slab, obj_exts, obj_to_index(s, slab, p));
}
/* Should be called only if mem_alloc_profiling_enabled() */
static noinline void
__alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags)
{
struct slabobj_ext *obj_exts;
struct slabobj_ext *obj_ext;
if (!object)
return;
@ -2314,14 +2319,14 @@ __alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags)
if (flags & __GFP_NO_OBJ_EXT)
return;
obj_exts = prepare_slab_obj_exts_hook(s, flags, object);
obj_ext = prepare_slab_obj_ext_hook(s, flags, object);
/*
* Currently obj_exts is used only for allocation profiling.
* If other users appear then mem_alloc_profiling_enabled()
* check should be added before alloc_tag_add().
*/
if (likely(obj_exts))
alloc_tag_add(&obj_exts->ref, current->alloc_tag, s->size);
if (likely(obj_ext))
alloc_tag_add(&obj_ext->ref, current->alloc_tag, s->size);
else
alloc_tag_set_inaccurate(current->alloc_tag);
}
@ -2338,8 +2343,8 @@ static noinline void
__alloc_tagging_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p,
int objects)
{
struct slabobj_ext *obj_exts;
int i;
unsigned long obj_exts;
/* slab->obj_exts might not be NULL if it was created for MEMCG accounting. */
if (s->flags & (SLAB_NO_OBJ_EXT | SLAB_NOLEAKTRACE))
@ -2352,7 +2357,7 @@ __alloc_tagging_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p
for (i = 0; i < objects; i++) {
unsigned int off = obj_to_index(s, slab, p[i]);
alloc_tag_sub(&obj_exts[off].ref, s->size);
alloc_tag_sub(&slab_obj_ext(slab, obj_exts, off)->ref, s->size);
}
}
@ -2411,7 +2416,7 @@ static __fastpath_inline
void memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p,
int objects)
{
struct slabobj_ext *obj_exts;
unsigned long obj_exts;
if (!memcg_kmem_online())
return;
@ -2426,7 +2431,8 @@ void memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p,
static __fastpath_inline
bool memcg_slab_post_charge(void *p, gfp_t flags)
{
struct slabobj_ext *slab_exts;
unsigned long obj_exts;
struct slabobj_ext *obj_ext;
struct kmem_cache *s;
struct page *page;
struct slab *slab;
@ -2467,10 +2473,11 @@ bool memcg_slab_post_charge(void *p, gfp_t flags)
return true;
/* Ignore already charged objects. */
slab_exts = slab_obj_exts(slab);
if (slab_exts) {
obj_exts = slab_obj_exts(slab);
if (obj_exts) {
off = obj_to_index(s, slab, p);
if (unlikely(slab_exts[off].objcg))
obj_ext = slab_obj_ext(slab, obj_exts, off);
if (unlikely(obj_ext->objcg))
return true;
}