Re: [PATCH v2 16/21] mm/slab: move kfree() from slab_common.c to slub.c

[Hyeonggon Yoo]

On Mon, Nov 20, 2023 at 07:34:27PM +0100, Vlastimil Babka wrote:
> This should result in better code. Currently kfree() makes a function
> call between compilation units to __kmem_cache_free() which does its own
> virt_to_slab(), throwing away the struct slab pointer we already had in
> kfree(). Now it can be reused. Additionally kfree() can now inline the
> whole SLUB freeing fastpath.
> 
> Also move over free_large_kmalloc() as the only callsites are now in
> slub.c, and make it static.
> 
> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
> ---
>  mm/slab.h        |  4 ----
>  mm/slab_common.c | 45 ---------------------------------------------
>  mm/slub.c        | 51 ++++++++++++++++++++++++++++++++++++++++++++++-----
>  3 files changed, 46 insertions(+), 54 deletions(-)
> 
> diff --git a/mm/slab.h b/mm/slab.h
> index 5ae6a978e9c2..35a55c4a407d 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -395,8 +395,6 @@ struct kmem_cache *kmalloc_slab(size_t size, gfp_t flags, unsigned long caller);
>  void *__kmem_cache_alloc_node(struct kmem_cache *s, gfp_t gfpflags,
>  			      int node, size_t orig_size,
>  			      unsigned long caller);
> -void __kmem_cache_free(struct kmem_cache *s, void *x, unsigned long caller);
> -
>  gfp_t kmalloc_fix_flags(gfp_t flags);
>  
>  /* Functions provided by the slab allocators */
> @@ -559,8 +557,6 @@ static inline int memcg_alloc_slab_cgroups(struct slab *slab,
>  }
>  #endif /* CONFIG_MEMCG_KMEM */
>  
> -void free_large_kmalloc(struct folio *folio, void *object);
> -
>  size_t __ksize(const void *objp);
>  
>  static inline size_t slab_ksize(const struct kmem_cache *s)
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index bbc2e3f061f1..f4f275613d2a 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -963,22 +963,6 @@ void __init create_kmalloc_caches(slab_flags_t flags)
>  	slab_state = UP;
>  }
>  
> -void free_large_kmalloc(struct folio *folio, void *object)
> -{
> -	unsigned int order = folio_order(folio);
> -
> -	if (WARN_ON_ONCE(order == 0))
> -		pr_warn_once("object pointer: 0x%p\n", object);
> -
> -	kmemleak_free(object);
> -	kasan_kfree_large(object);
> -	kmsan_kfree_large(object);
> -
> -	mod_lruvec_page_state(folio_page(folio, 0), NR_SLAB_UNRECLAIMABLE_B,
> -			      -(PAGE_SIZE << order));
> -	__free_pages(folio_page(folio, 0), order);
> -}
> -
>  static void *__kmalloc_large_node(size_t size, gfp_t flags, int node);
>  static __always_inline
>  void *__do_kmalloc_node(size_t size, gfp_t flags, int node, unsigned long caller)
> @@ -1023,35 +1007,6 @@ void *__kmalloc_node_track_caller(size_t size, gfp_t flags,
>  }
>  EXPORT_SYMBOL(__kmalloc_node_track_caller);
>  
> -/**
> - * kfree - free previously allocated memory
> - * @object: pointer returned by kmalloc() or kmem_cache_alloc()
> - *
> - * If @object is NULL, no operation is performed.
> - */
> -void kfree(const void *object)
> -{
> -	struct folio *folio;
> -	struct slab *slab;
> -	struct kmem_cache *s;
> -
> -	trace_kfree(_RET_IP_, object);
> -
> -	if (unlikely(ZERO_OR_NULL_PTR(object)))
> -		return;
> -
> -	folio = virt_to_folio(object);
> -	if (unlikely(!folio_test_slab(folio))) {
> -		free_large_kmalloc(folio, (void *)object);
> -		return;
> -	}
> -
> -	slab = folio_slab(folio);
> -	s = slab->slab_cache;
> -	__kmem_cache_free(s, (void *)object, _RET_IP_);
> -}
> -EXPORT_SYMBOL(kfree);
> -
>  /**
>   * __ksize -- Report full size of underlying allocation
>   * @object: pointer to the object
> diff --git a/mm/slub.c b/mm/slub.c
> index cc801f8258fe..2baa9e94d9df 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -4197,11 +4197,6 @@ static inline struct kmem_cache *cache_from_obj(struct kmem_cache *s, void *x)
>  	return cachep;
>  }
>  
> -void __kmem_cache_free(struct kmem_cache *s, void *x, unsigned long caller)
> -{
> -	slab_free(s, virt_to_slab(x), x, NULL, &x, 1, caller);
> -}
> -
>  /**
>   * kmem_cache_free - Deallocate an object
>   * @s: The cache the allocation was from.
> @@ -4220,6 +4215,52 @@ void kmem_cache_free(struct kmem_cache *s, void *x)
>  }
>  EXPORT_SYMBOL(kmem_cache_free);
>  
> +static void free_large_kmalloc(struct folio *folio, void *object)
> +{
> +	unsigned int order = folio_order(folio);
> +
> +	if (WARN_ON_ONCE(order == 0))
> +		pr_warn_once("object pointer: 0x%p\n", object);
> +
> +	kmemleak_free(object);
> +	kasan_kfree_large(object);
> +	kmsan_kfree_large(object);
> +
> +	mod_lruvec_page_state(folio_page(folio, 0), NR_SLAB_UNRECLAIMABLE_B,
> +			      -(PAGE_SIZE << order));
> +	__free_pages(folio_page(folio, 0), order);
> +}
> +
> +/**
> + * kfree - free previously allocated memory
> + * @object: pointer returned by kmalloc() or kmem_cache_alloc()
> + *
> + * If @object is NULL, no operation is performed.
> + */
> +void kfree(const void *object)
> +{
> +	struct folio *folio;
> +	struct slab *slab;
> +	struct kmem_cache *s;
> +	void *x = (void *)object;
> +
> +	trace_kfree(_RET_IP_, object);
> +
> +	if (unlikely(ZERO_OR_NULL_PTR(object)))
> +		return;
> +
> +	folio = virt_to_folio(object);
> +	if (unlikely(!folio_test_slab(folio))) {
> +		free_large_kmalloc(folio, (void *)object);
> +		return;
> +	}
> +
> +	slab = folio_slab(folio);
> +	s = slab->slab_cache;
> +	slab_free(s, slab, x, NULL, &x, 1, _RET_IP_);
> +}
> +EXPORT_SYMBOL(kfree);
> +
>  struct detached_freelist {
>  	struct slab *slab;
>  	void *tail;

Looks good to me,
Reviewed-by: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>

nit: mm/kfence/report.c checks if a function name starts with
"__kmem_cache_free" which is removed by this patch.

> 
> -- 
> 2.42.1
> 
>