Re: [PATCH v4 04/22] mm/slab: move and refactor __kmem_cache_alias()

Liam R. Howlett
2026-01-27T16:17:33Z

* Vlastimil Babka <vbabka@suse.cz> [260123 01:53]:
> Move __kmem_cache_alias() to slab_common.c since it's called by
> __kmem_cache_create_args() and calls find_mergeable() that both
> are in this file. We can remove two slab.h declarations and make
> them static. Instead declare sysfs_slab_alias() from slub.c so
> that __kmem_cache_alias() can keep calling it.
>
> Add args parameter to __kmem_cache_alias() and find_mergeable() instead
> of align and ctor. With that we can also move the checks for usersize
> and sheaf_capacity there from __kmem_cache_create_args() and make the
> result more symmetric with slab_unmergeable().
>
> No functional changes intended.
>
> Reviewed-by: Harry Yoo <harry.yoo@oracle.com>
> Reviewed-by: Suren Baghdasaryan <surenb@google.com>
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

One nit.

Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>

> ---
> mm/slab.h | 8 +++-----
> mm/slab_common.c | 44 +++++++++++++++++++++++++++++++++++++-------
> mm/slub.c | 30 +-----------------------------
> 3 files changed, 41 insertions(+), 41 deletions(-)
>
> diff --git a/mm/slab.h b/mm/slab.h
> index e767aa7e91b0..cb48ce5014ba 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -281,9 +281,12 @@ struct kmem_cache {
> #define SLAB_SUPPORTS_SYSFS 1
> void sysfs_slab_unlink(struct kmem_cache *s);
> void sysfs_slab_release(struct kmem_cache *s);
> +int sysfs_slab_alias(struct kmem_cache *, const char *);

nit: the names of the variables are missing. I guess because they were
missing before. *s and *name, I guess, although they are *s and *p
in the other declaration.

> #else
> static inline void sysfs_slab_unlink(struct kmem_cache *s) { }
> static inline void sysfs_slab_release(struct kmem_cache *s) { }
> +static inline int sysfs_slab_alias(struct kmem_cache *s, const char *p)
> + { return 0; }
> #endif
>
> void *fixup_red_left(struct kmem_cache *s, void *p);
> @@ -400,11 +403,6 @@ extern void create_boot_cache(struct kmem_cache *, const char *name,
> unsigned int useroffset, unsigned int usersize);
>
> int slab_unmergeable(struct kmem_cache *s);
> -struct kmem_cache *find_mergeable(unsigned size, unsigned align,
> - slab_flags_t flags, const char *name, void (*ctor)(void *));
> -struct kmem_cache *
> -__kmem_cache_alias(const char *name, unsigned int size, unsigned int align,
> - slab_flags_t flags, void (*ctor)(void *));
>
> slab_flags_t kmem_cache_flags(slab_flags_t flags, const char *name);
>
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index e691ede0e6a8..ee245a880603 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -174,15 +174,22 @@ int slab_unmergeable(struct kmem_cache *s)
> return 0;
> }
>
> -struct kmem_cache *find_mergeable(unsigned int size, unsigned int align,
> - slab_flags_t flags, const char *name, void (*ctor)(void *))
> +static struct kmem_cache *find_mergeable(unsigned int size, slab_flags_t flags,
> + const char *name, struct kmem_cache_args *args)
> {
> struct kmem_cache *s;
> + unsigned int align;
>
> if (slab_nomerge)
> return NULL;
>
> - if (ctor)
> + if (args->ctor)
> + return NULL;
> +
> + if (IS_ENABLED(CONFIG_HARDENED_USERCOPY) && args->usersize)
> + return NULL;
> +
> + if (args->sheaf_capacity)
> return NULL;
>
> flags = kmem_cache_flags(flags, name);
> @@ -191,7 +198,7 @@ struct kmem_cache *find_mergeable(unsigned int size, unsigned int align,
> return NULL;
>
> size = ALIGN(size, sizeof(void *));
> - align = calculate_alignment(flags, align, size);
> + align = calculate_alignment(flags, args->align, size);
> size = ALIGN(size, align);
>
> list_for_each_entry_reverse(s, &slab_caches, list) {
> @@ -252,6 +259,31 @@ static struct kmem_cache *create_cache(const char *name,
> return ERR_PTR(err);
> }
>
> +static struct kmem_cache *
> +__kmem_cache_alias(const char *name, unsigned int size, slab_flags_t flags,
> + struct kmem_cache_args *args)
> +{
> + struct kmem_cache *s;
> +
> + s = find_mergeable(size, flags, name, args);
> + if (s) {
> + if (sysfs_slab_alias(s, name))
> + pr_err("SLUB: Unable to add cache alias %s to sysfs\n",
> + name);
> +
> + s->refcount++;
> +
> + /*
> + * Adjust the object sizes so that we clear
> + * the complete object on kzalloc.
> + */
> + s->object_size = max(s->object_size, size);
> + s->inuse = max(s->inuse, ALIGN(size, sizeof(void *)));
> + }
> +
> + return s;
> +}
> +
> /**
> * __kmem_cache_create_args - Create a kmem cache.
> * @name: A string which is used in /proc/slabinfo to identify this cache.
> @@ -323,9 +355,7 @@ struct kmem_cache *__kmem_cache_create_args(const char *name,
> object_size - args->usersize < args->useroffset))
> args->usersize = args->useroffset = 0;
>
> - if (!args->usersize && !args->sheaf_capacity)
> - s = __kmem_cache_alias(name, object_size, args->align, flags,
> - args->ctor);
> + s = __kmem_cache_alias(name, object_size, flags, args);
> if (s)
> goto out_unlock;
>
> diff --git a/mm/slub.c b/mm/slub.c
> index 4eb60e99abd7..9d86c0505dcd 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -350,11 +350,8 @@ enum track_item { TRACK_ALLOC, TRACK_FREE };
>
> #ifdef SLAB_SUPPORTS_SYSFS
> static int sysfs_slab_add(struct kmem_cache *);
> -static int sysfs_slab_alias(struct kmem_cache *, const char *);
> #else
> static inline int sysfs_slab_add(struct kmem_cache *s) { return 0; }
> -static inline int sysfs_slab_alias(struct kmem_cache *s, const char *p)
> - { return 0; }
> #endif
>
> #if defined(CONFIG_DEBUG_FS) && defined(CONFIG_SLUB_DEBUG)
> @@ -8570,31 +8567,6 @@ void __init kmem_cache_init_late(void)
> WARN_ON(!flushwq);
> }
>
> -struct kmem_cache *
> -__kmem_cache_alias(const char *name, unsigned int size, unsigned int align,
> - slab_flags_t flags, void (*ctor)(void *))
> -{
> - struct kmem_cache *s;
> -
> - s = find_mergeable(size, align, flags, name, ctor);
> - if (s) {
> - if (sysfs_slab_alias(s, name))
> - pr_err("SLUB: Unable to add cache alias %s to sysfs\n",
> - name);
> -
> - s->refcount++;
> -
> - /*
> - * Adjust the object sizes so that we clear
> - * the complete object on kzalloc.
> - */
> - s->object_size = max(s->object_size, size);
> - s->inuse = max(s->inuse, ALIGN(size, sizeof(void *)));
> - }
> -
> - return s;
> -}
> -
> int do_kmem_cache_create(struct kmem_cache *s, const char *name,
> unsigned int size, struct kmem_cache_args *args,
> slab_flags_t flags)
> @@ -9827,7 +9799,7 @@ struct saved_alias {
>
> static struct saved_alias *alias_list;
>
> -static int sysfs_slab_alias(struct kmem_cache *s, const char *name)
> +int sysfs_slab_alias(struct kmem_cache *s, const char *name)
> {
> struct saved_alias *al;
>
>
> --
> 2.52.0
>