Commit 7a8e71bc authored by Harry Yoo's avatar Harry Yoo Committed by Vlastimil Babka
Browse files

mm/slab: use stride to access slabobj_ext 



Use a configurable stride value when accessing slab object extension
metadata instead of assuming a fixed sizeof(struct slabobj_ext).

Store stride value in free bits of slab->counters field. This allows
for flexibility in cases where the extension is embedded within
slab objects.

Since these free bits exist only on 64-bit, any future optimizations
that need to change stride value cannot be enabled on 32-bit architectures.

Suggested-by: default avatarVlastimil Babka <vbabka@suse.cz>
Reviewed-by: default avatarSuren Baghdasaryan <surenb@google.com>
Signed-off-by: default avatarHarry Yoo <harry.yoo@oracle.com>
Link: https://patch.msgid.link/20260113061845.159790-6-harry.yoo@oracle.com


Signed-off-by: default avatarVlastimil Babka <vbabka@suse.cz>
parent 52f1ca8a

mm/slab.h

+33 −4
Original line number Diff line number Diff line
@@ -55,6 +55,14 @@ struct freelist_counters { 
					 * that the slab was corrupted

					 */

					unsigned frozen:1;

#ifdef CONFIG_64BIT

					/*

					 * Some optimizations use free bits in 'counters' field

					 * to save memory. In case ->stride field is not available,

					 * such optimizations are disabled.

					 */

					unsigned short stride;

#endif

				};

			};

		};
@@ -529,6 +537,26 @@ static inline unsigned long slab_obj_exts(struct slab *slab) 
	return obj_exts & ~OBJEXTS_FLAGS_MASK;

}



#ifdef CONFIG_64BIT

static inline void slab_set_stride(struct slab *slab, unsigned short stride)

{

	slab->stride = stride;

}

static inline unsigned short slab_get_stride(struct slab *slab)

{

	return slab->stride;

}

#else

static inline void slab_set_stride(struct slab *slab, unsigned short stride)

{

	VM_WARN_ON_ONCE(stride != sizeof(struct slabobj_ext));

}

static inline unsigned short slab_get_stride(struct slab *slab)

{

	return sizeof(struct slabobj_ext);

}

#endif



/*

 * slab_obj_ext - get the pointer to the slab object extension metadata

 * associated with an object in a slab.
@@ -542,12 +570,9 @@ 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];

	return (struct slabobj_ext *)(obj_exts + slab_get_stride(slab) * index);

}



int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,
@@ -567,6 +592,10 @@ static inline struct slabobj_ext *slab_obj_ext(struct slab *slab, 
	return NULL;

}



static inline void slab_set_stride(struct slab *slab, unsigned int stride) { }

static inline unsigned int slab_get_stride(struct slab *slab) { return 0; }





#endif /* CONFIG_SLAB_OBJ_EXT */



static inline enum node_stat_item cache_vmstat_idx(struct kmem_cache *s)

mm/slub.c

+2 −0
Original line number Diff line number Diff line
@@ -2206,6 +2206,8 @@ int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s, 
retry:

	old_exts = READ_ONCE(slab->obj_exts);

	handle_failed_objexts_alloc(old_exts, vec, objects);

	slab_set_stride(slab, sizeof(struct slabobj_ext));



	if (new_slab) {

		/*

		 * If the slab is brand new and nobody can yet access its