Re: [PATCH v4 1/4] mm/slub: enable debugging memory wasting of kmalloc

[Hyeonggon Yoo]

On Mon, Aug 29, 2022 at 03:56:15PM +0800, Feng Tang wrote:
> kmalloc's API family is critical for mm, with one nature that it will
> round up the request size to a fixed one (mostly power of 2). Say
> when user requests memory for '2^n + 1' bytes, actually 2^(n+1) bytes
> could be allocated, so in worst case, there is around 50% memory
> space waste.
> 

[...]

>  static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
> -			  unsigned long addr, struct kmem_cache_cpu *c)
> +			  unsigned long addr, struct kmem_cache_cpu *c, unsigned int orig_size)
>  {
>  	void *freelist;
>  	struct slab *slab;
> @@ -3115,6 +3158,7 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
>  
>  		if (s->flags & SLAB_STORE_USER)
>  			set_track(s, freelist, TRACK_ALLOC, addr);
> +		set_orig_size(s, freelist, orig_size);
>  
>  		return freelist;
>  	}
> @@ -3140,6 +3184,8 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
>  		 */
>  		if (s->flags & SLAB_STORE_USER)
>  			set_track(s, freelist, TRACK_ALLOC, addr);
> +		set_orig_size(s, freelist, orig_size);
> +
>  		return freelist;
>  	}

Maybe we can move set_track() and set_orig_size() to after slab_post_alloc_hook().
something like alloc/free hooks for debugging caches? (and drop orig_size parameter.) 

Thanks!

>  
> @@ -3182,7 +3228,7 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
>   * pointer.
>   */
>  static void *__slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
> -			  unsigned long addr, struct kmem_cache_cpu *c)
> +			  unsigned long addr, struct kmem_cache_cpu *c, unsigned int orig_size)
>  {
>  	void *p;

-- 
Thanks,
Hyeonggon