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Message-ID: <20251027122847.320924-4-harry.yoo@oracle.com>
Date: Mon, 27 Oct 2025 21:28:43 +0900
From: Harry Yoo <harry.yoo@...cle.com>
To: akpm@...ux-foundation.org, vbabka@...e.cz
Cc: andreyknvl@...il.com, cl@...ux.com, dvyukov@...gle.com, glider@...gle.com,
hannes@...xchg.org, linux-mm@...ck.org, mhocko@...nel.org,
muchun.song@...ux.dev, rientjes@...gle.com, roman.gushchin@...ux.dev,
ryabinin.a.a@...il.com, shakeel.butt@...ux.dev, surenb@...gle.com,
vincenzo.frascino@....com, yeoreum.yun@....com, harry.yoo@...cle.com,
tytso@....edu, adilger.kernel@...ger.ca, linux-ext4@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: [RFC PATCH V3 3/7] mm/slab: abstract slabobj_ext access via new slab_obj_ext() helper
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@...cle.com>
---
mm/memcontrol.c | 23 ++++++++++++++++-------
mm/slab.h | 43 ++++++++++++++++++++++++++++++++++++------
mm/slub.c | 50 ++++++++++++++++++++++++++++---------------------
3 files changed, 82 insertions(+), 34 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 8dd7fbed5a94..2a9dc246e802 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2566,7 +2566,8 @@ struct mem_cgroup *mem_cgroup_from_obj_folio(struct folio *folio, void *p)
* slab->obj_exts.
*/
if (folio_test_slab(folio)) {
- struct slabobj_ext *obj_exts;
+ unsigned long obj_exts;
+ struct slabobj_ext *obj_ext;
struct slab *slab;
unsigned int off;
@@ -2576,8 +2577,9 @@ struct mem_cgroup *mem_cgroup_from_obj_folio(struct folio *folio, 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;
}
@@ -3168,6 +3170,9 @@ 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) &&
@@ -3190,29 +3195,33 @@ 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);
diff --git a/mm/slab.h b/mm/slab.h
index d63cc9b5e313..df2c987d950d 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -528,10 +528,12 @@ 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);
@@ -544,7 +546,30 @@ 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(!slab_obj_exts(slab));
+ 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,
@@ -552,7 +577,13 @@ 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 false;
+}
+
+static inline struct slabobj_ext *slab_obj_ext(struct slab *slab,
+ unsigned int index)
{
return NULL;
}
@@ -569,7 +600,7 @@ 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);
diff --git a/mm/slub.c b/mm/slub.c
index 64705cb3734f..ae73403f8c29 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2031,7 +2031,7 @@ 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);
@@ -2039,9 +2039,12 @@ 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);
+
/* codetag should be NULL */
- WARN_ON(slab_exts[offs].ref.ct);
- set_codetag_empty(&slab_exts[offs].ref);
+ WARN_ON(ext->ref.ct);
+ set_codetag_empty(&ext->ref);
}
}
@@ -2159,7 +2162,7 @@ int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,
static inline void free_slab_obj_exts(struct slab *slab)
{
- struct slabobj_ext *obj_exts;
+ unsigned long obj_exts;
obj_exts = slab_obj_exts(slab);
if (!obj_exts)
@@ -2172,11 +2175,11 @@ static inline void free_slab_obj_exts(struct slab *slab)
* NULL, therefore replace NULL with CODETAG_EMPTY to indicate that
* the extension for obj_exts is expected to be NULL.
*/
- mark_objexts_empty(obj_exts);
+ mark_objexts_empty((struct slabobj_ext *)obj_exts);
if (unlikely(READ_ONCE(slab->obj_exts) & OBJEXTS_NOSPIN_ALLOC))
- kfree_nolock(obj_exts);
+ kfree_nolock((void *)obj_exts);
else
- kfree(obj_exts);
+ kfree((void *)obj_exts);
slab->obj_exts = 0;
}
@@ -2201,9 +2204,10 @@ 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;
if (!p)
return NULL;
@@ -2215,30 +2219,32 @@ prepare_slab_obj_exts_hook(struct kmem_cache *s, gfp_t flags, void *p)
return NULL;
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;
- 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);
}
static inline void
@@ -2253,8 +2259,8 @@ 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))
@@ -2267,7 +2273,7 @@ __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);
}
}
@@ -2326,7 +2332,7 @@ 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;
@@ -2341,7 +2347,8 @@ 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 folio *folio;
struct slab *slab;
@@ -2381,10 +2388,11 @@ 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;
}
--
2.43.0
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