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

[Feng Tang]

On Wed, Aug 31, 2022 at 10:52:15PM +0800, Hyeonggon Yoo wrote:
> 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.) 

Yep, we discussed this during v3 review
https://lore.kernel.org/lkml/442d2b9c-9f07-8954-b90e-b4a9f8b64303@xxxxxxxxx/

Will revisit this considering recent refactoring and the following
kmalloc data redzone patches.

Thanks,
Feng

> Thanks!