On 6/15/24 12:59 AM, Suren Baghdasaryan wrote:
> slab_post_alloc_hook() uses prepare_slab_obj_exts_hook() to obtain
> slabobj_ext object. Currently the only user of slabobj_ext object in
> this path is memory allocation profiling, therefore when it's not enabled
> this object is not needed. This also generates a warning when compiling
> with CONFIG_MEM_ALLOC_PROFILING=n. Move the code under this configuration
> to fix the warning. If more slabobj_ext users appear in the future, the
> code will have to be changed back to call prepare_slab_obj_exts_hook().
>
> Fixes: 4b8736964640 ("mm/slab: add allocation accounting into slab allocation and free paths")
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
> Closes: https://lore.kernel.org/oe-kbuild-all/202406150444.F6neSaiy-lkp@xxxxxxxxx/
> Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
But it seems to me we could remove the whole #ifdef if current->alloc_tag
(which doesn't exist with !MEM_ALLOC_PROFILING) had an access helper, or
there was a alloc_tag_add_current() variant?
> ---
> mm/slub.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index 1373ac365a46..4927edec6a8c 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -3902,7 +3902,6 @@ bool slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *lru,
> unsigned int orig_size)
> {
> unsigned int zero_size = s->object_size;
> - struct slabobj_ext *obj_exts;
> bool kasan_init = init;
> size_t i;
> gfp_t init_flags = flags & gfp_allowed_mask;
> @@ -3945,9 +3944,11 @@ bool slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *lru,
> kmemleak_alloc_recursive(p[i], s->object_size, 1,
> s->flags, init_flags);
> kmsan_slab_alloc(s, p[i], init_flags);
> +#ifdef CONFIG_MEM_ALLOC_PROFILING
> if (need_slab_obj_ext()) {
> + struct slabobj_ext *obj_exts;
> +
> obj_exts = prepare_slab_obj_exts_hook(s, flags, p[i]);
> -#ifdef CONFIG_MEM_ALLOC_PROFILING
> /*
> * Currently obj_exts is used only for allocation profiling.
> * If other users appear then mem_alloc_profiling_enabled()
> @@ -3955,8 +3956,8 @@ bool slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *lru,
> */
> if (likely(obj_exts))
> alloc_tag_add(&obj_exts->ref, current->alloc_tag, s->size);
> -#endif
> }
> +#endif
> }
>
> return memcg_slab_post_alloc_hook(s, lru, flags, size, p);
>
> base-commit: c286c21ff94252f778515b21b6bebe749454a852
