Re: [PATCH v2 17/21] mm/slab: move kmalloc_slab() to mm/slab.h

[Hyeonggon Yoo <42.hyeyoo@gmail.com>]

On Mon, Nov 20, 2023 at 07:34:28PM +0100, Vlastimil Babka wrote:
> In preparation for the next patch, move the kmalloc_slab() function to
> the header, as it will have callers from two files, and make it inline.
> To avoid unnecessary bloat, remove all size checks/warnings from
> kmalloc_slab() as they just duplicate those in callers, especially after
> recent changes to kmalloc_size_roundup(). We just need to adjust handling
> of zero size in __do_kmalloc_node(). Also we can stop handling NULL
> result from kmalloc_slab() there as that now cannot happen (unless
> called too early during boot).
> 
> The size_index array becomes visible so rename it to a more specific
> kmalloc_size_index.
> 
> Reviewed-by: Kees Cook <keescook@chromium.org>
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> ---
>  mm/slab.h        | 28 ++++++++++++++++++++++++++--
>  mm/slab_common.c | 43 ++++++++-----------------------------------
>  2 files changed, 34 insertions(+), 37 deletions(-)
> 
> diff --git a/mm/slab.h b/mm/slab.h
> index 35a55c4a407d..7d7cc7af614e 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -389,8 +389,32 @@ extern const struct kmalloc_info_struct {
>  void setup_kmalloc_cache_index_table(void);
>  void create_kmalloc_caches(slab_flags_t);
>  
> -/* Find the kmalloc slab corresponding for a certain size */
> -struct kmem_cache *kmalloc_slab(size_t size, gfp_t flags, unsigned long caller);
> +extern u8 kmalloc_size_index[24];
> +
> +static inline unsigned int size_index_elem(unsigned int bytes)
> +{
> +	return (bytes - 1) / 8;
> +}
> +
> +/*
> + * Find the kmem_cache structure that serves a given size of
> + * allocation
> + *
> + * This assumes size is larger than zero and not larger than
> + * KMALLOC_MAX_CACHE_SIZE and the caller must check that.
> + */
> +static inline struct kmem_cache *
> +kmalloc_slab(size_t size, gfp_t flags, unsigned long caller)
> +{
> +	unsigned int index;
> +
> +	if (size <= 192)
> +		index = kmalloc_size_index[size_index_elem(size)];
> +	else
> +		index = fls(size - 1);
> +
> +	return kmalloc_caches[kmalloc_type(flags, caller)][index];
> +}
>  
>  void *__kmem_cache_alloc_node(struct kmem_cache *s, gfp_t gfpflags,
>  			      int node, size_t orig_size,
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index f4f275613d2a..31ade17a7ad9 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -665,7 +665,7 @@ EXPORT_SYMBOL(random_kmalloc_seed);
>   * of two cache sizes there. The size of larger slabs can be determined using
>   * fls.
>   */
> -static u8 size_index[24] __ro_after_init = {
> +u8 kmalloc_size_index[24] __ro_after_init = {
>  	3,	/* 8 */
>  	4,	/* 16 */
>  	5,	/* 24 */
> @@ -692,33 +692,6 @@ static u8 size_index[24] __ro_after_init = {
>  	2	/* 192 */
>  };
>  
> -static inline unsigned int size_index_elem(unsigned int bytes)
> -{
> -	return (bytes - 1) / 8;
> -}
> -
> -/*
> - * Find the kmem_cache structure that serves a given size of
> - * allocation
> - */
> -struct kmem_cache *kmalloc_slab(size_t size, gfp_t flags, unsigned long caller)
> -{
> -	unsigned int index;
> -
> -	if (size <= 192) {
> -		if (!size)
> -			return ZERO_SIZE_PTR;
> -
> -		index = size_index[size_index_elem(size)];
> -	} else {
> -		if (WARN_ON_ONCE(size > KMALLOC_MAX_CACHE_SIZE))
> -			return NULL;
> -		index = fls(size - 1);
> -	}
> -
> -	return kmalloc_caches[kmalloc_type(flags, caller)][index];
> -}
> -
>  size_t kmalloc_size_roundup(size_t size)
>  {
>  	if (size && size <= KMALLOC_MAX_CACHE_SIZE) {
> @@ -843,9 +816,9 @@ void __init setup_kmalloc_cache_index_table(void)
>  	for (i = 8; i < KMALLOC_MIN_SIZE; i += 8) {
>  		unsigned int elem = size_index_elem(i);
>  
> -		if (elem >= ARRAY_SIZE(size_index))
> +		if (elem >= ARRAY_SIZE(kmalloc_size_index))
>  			break;
> -		size_index[elem] = KMALLOC_SHIFT_LOW;
> +		kmalloc_size_index[elem] = KMALLOC_SHIFT_LOW;
>  	}
>  
>  	if (KMALLOC_MIN_SIZE >= 64) {
> @@ -854,7 +827,7 @@ void __init setup_kmalloc_cache_index_table(void)
>  		 * is 64 byte.
>  		 */
>  		for (i = 64 + 8; i <= 96; i += 8)
> -			size_index[size_index_elem(i)] = 7;
> +			kmalloc_size_index[size_index_elem(i)] = 7;
>  
>  	}
>  
> @@ -865,7 +838,7 @@ void __init setup_kmalloc_cache_index_table(void)
>  		 * instead.
>  		 */
>  		for (i = 128 + 8; i <= 192; i += 8)
> -			size_index[size_index_elem(i)] = 8;
> +			kmalloc_size_index[size_index_elem(i)] = 8;
>  	}
>  }
>  
> @@ -977,10 +950,10 @@ void *__do_kmalloc_node(size_t size, gfp_t flags, int node, unsigned long caller
>  		return ret;
>  	}
>  
> -	s = kmalloc_slab(size, flags, caller);
> +	if (unlikely(!size))
> +		return ZERO_SIZE_PTR;
>  
> -	if (unlikely(ZERO_OR_NULL_PTR(s)))
> -		return s;
> +	s = kmalloc_slab(size, flags, caller);
>  
>  	ret = __kmem_cache_alloc_node(s, flags, node, size, caller);
>  	ret = kasan_kmalloc(s, ret, size, flags);
> 
> -- 

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

> 2.42.1
> 
>