[PATCH RFC 04/12] mm/slab: make slab_obj_ext() determine object index
From: Vlastimil Babka (SUSE)
Date: Wed Jul 15 2026 - 06:11:57 EST
All callers perform the same obj_to_index() calculation to pass the
index. Simplify by passing object pointer instead and determining the
index by slab_obj_ext().
Signed-off-by: Vlastimil Babka (SUSE) <vbabka@xxxxxxxxxx>
---
mm/memcontrol.c | 12 +++---------
mm/slab.h | 14 ++++++++------
mm/slub.c | 22 +++++++---------------
3 files changed, 18 insertions(+), 30 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 6dc4888a90f3..4e427286a88a 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2865,15 +2865,13 @@ struct mem_cgroup *mem_cgroup_from_obj_slab(struct slab *slab, void *p)
*/
unsigned long obj_exts;
struct slabobj_ext *obj_ext;
- unsigned int off;
obj_exts = slab_obj_exts(slab);
if (!obj_exts)
return NULL;
get_slab_obj_exts(obj_exts);
- off = obj_to_index(slab->slab_cache, slab, p);
- obj_ext = slab_obj_ext(slab, obj_exts, off);
+ obj_ext = slab_obj_ext(slab->slab_cache, slab, obj_exts, p);
if (obj_ext->objcg) {
struct obj_cgroup *objcg = obj_ext->objcg;
@@ -3541,7 +3539,6 @@ bool __memcg_slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *lru,
size_t obj_size = obj_full_size(s);
struct obj_cgroup *objcg;
struct slab *slab;
- unsigned long off;
size_t i;
/*
@@ -3616,8 +3613,7 @@ bool __memcg_slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *lru,
obj_exts = slab_obj_exts(slab);
get_slab_obj_exts(obj_exts);
- off = obj_to_index(s, slab, p[i]);
- obj_ext = slab_obj_ext(slab, obj_exts, off);
+ obj_ext = slab_obj_ext(s, slab, obj_exts, p[i]);
obj_cgroup_get(objcg);
obj_ext->objcg = objcg;
put_slab_obj_exts(obj_exts);
@@ -3635,10 +3631,8 @@ void __memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab,
struct obj_cgroup *objcg;
struct slabobj_ext *obj_ext;
struct obj_stock_pcp *stock;
- unsigned int off;
- off = obj_to_index(s, slab, p[i]);
- obj_ext = slab_obj_ext(slab, obj_exts, off);
+ obj_ext = slab_obj_ext(s, slab, obj_exts, p[i]);
objcg = obj_ext->objcg;
if (!objcg)
continue;
diff --git a/mm/slab.h b/mm/slab.h
index 7bd361447c54..36d067d6e7c0 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -646,14 +646,16 @@ static inline unsigned int slab_get_stride(struct slab *slab)
* Returns a pointer to the object extension associated with the object.
* Must be called within a section covered by get/put_slab_obj_exts().
*/
-static inline struct slabobj_ext *slab_obj_ext(struct slab *slab,
- unsigned long obj_exts,
- unsigned int index)
+static inline struct slabobj_ext *
+slab_obj_ext(struct kmem_cache *s, struct slab *slab, unsigned long obj_exts,
+ const void *obj)
{
struct slabobj_ext *obj_ext;
+ unsigned int index;
VM_WARN_ON_ONCE(obj_exts != slab_obj_exts(slab));
+ index = obj_to_index(s, slab, obj);
obj_ext = (struct slabobj_ext *)(obj_exts +
slab_get_stride(slab) * index);
return kasan_reset_tag(obj_ext);
@@ -669,9 +671,9 @@ 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)
+static inline struct slabobj_ext *
+slab_obj_ext(struct kmem_cache *s, struct slab *slab, unsigned long obj_exts,
+ const void *obj)
{
return NULL;
}
diff --git a/mm/slub.c b/mm/slub.c
index 9e25f2dce7a6..5e3f53bcd0d3 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2070,11 +2070,10 @@ static inline void mark_obj_codetag_empty(const void *obj)
obj_slab = virt_to_slab(obj);
slab_exts = slab_obj_exts(obj_slab);
if (slab_exts) {
+ struct slabobj_ext *ext;
+
get_slab_obj_exts(slab_exts);
- unsigned int offs = obj_to_index(obj_slab->slab_cache,
- obj_slab, obj);
- struct slabobj_ext *ext = slab_obj_ext(obj_slab,
- slab_exts, offs);
+ ext = slab_obj_ext(obj_slab->slab_cache, obj_slab, slab_exts, obj);
if (unlikely(is_codetag_empty(&ext->ref))) {
put_slab_obj_exts(slab_exts);
@@ -2362,10 +2361,8 @@ __alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags,
* check should be added before alloc_tag_add().
*/
if (obj_exts) {
- unsigned int obj_idx = obj_to_index(s, slab, object);
-
get_slab_obj_exts(obj_exts);
- obj_ext = slab_obj_ext(slab, obj_exts, obj_idx);
+ obj_ext = slab_obj_ext(s, slab, obj_exts, object);
alloc_tag_add(&obj_ext->ref, current->alloc_tag, s->size);
put_slab_obj_exts(obj_exts);
} else {
@@ -2386,7 +2383,6 @@ static noinline void
__alloc_tagging_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p,
int objects)
{
- int i;
unsigned long obj_exts;
/* slab->obj_exts might not be NULL if it was created for MEMCG accounting. */
@@ -2398,13 +2394,11 @@ __alloc_tagging_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p
return;
get_slab_obj_exts(obj_exts);
- for (i = 0; i < objects; i++) {
- unsigned int off = obj_to_index(s, slab, p[i]);
-
+ for (int i = 0; i < objects; i++) {
if (is_kfence_address(p[i]))
continue;
- alloc_tag_sub(&slab_obj_ext(slab, obj_exts, off)->ref, s->size);
+ alloc_tag_sub(&slab_obj_ext(s, slab, obj_exts, p[i])->ref, s->size);
}
put_slab_obj_exts(obj_exts);
}
@@ -2489,7 +2483,6 @@ bool memcg_slab_post_charge(void *p, gfp_t flags)
struct kmem_cache *s;
struct page *page;
struct slab *slab;
- unsigned long off;
page = virt_to_page(p);
if (PageLargeKmalloc(page)) {
@@ -2529,8 +2522,7 @@ bool memcg_slab_post_charge(void *p, gfp_t flags)
obj_exts = slab_obj_exts(slab);
if (obj_exts) {
get_slab_obj_exts(obj_exts);
- off = obj_to_index(s, slab, p);
- obj_ext = slab_obj_ext(slab, obj_exts, off);
+ obj_ext = slab_obj_ext(s, slab, obj_exts, p);
if (unlikely(obj_ext->objcg)) {
put_slab_obj_exts(obj_exts);
return true;
--
2.55.0