Re: [PATCH net-next v3] net: skb: isolate skb data area allocations into a separate bucket

[Pedro Falcato <pfalcato@suse.de>]

On Wed, Jul 08, 2026 at 10:30:50AM +0200, Paolo Abeni wrote:
> On 7/2/26 7:07 PM, Pedro Falcato wrote:> @@ -586,6 +586,8 @@ struct
> sk_buff *napi_build_skb(void *data, unsigned int frag_size)
> >  }
> >  EXPORT_SYMBOL(napi_build_skb);
> >  
> > +static kmem_buckets *skb_data_buckets __ro_after_init;
> > +
> >  static void *kmalloc_pfmemalloc(size_t obj_size, gfp_t flags, int node)
> >  {
> >  	if (!gfp_pfmemalloc_allowed(flags))
> > @@ -593,7 +595,8 @@ static void *kmalloc_pfmemalloc(size_t obj_size, gfp_t flags, int node)
> >  	if (!obj_size)
> >  		return kmem_cache_alloc_node(net_hotdata.skb_small_head_cache,
> >  					     flags, node);
> > -	return kmalloc_node_track_caller(obj_size, flags, node);
> > +	return kmem_buckets_alloc_node_track_caller(skb_data_buckets, obj_size,
> > +						    flags, node);
> 
> Sashiko noted that some drivers may require GFP_DMA buckets, and the
> above may break them:
> 
> https://sashiko.dev/#/patchset/20260702170728.168755-1-pfalcato%40suse.de

Oh, this is really awkward. Adding linux-mm and slab maintainers for input here.

Considering the current slab bucketing does not seem to duplicate DMA or
CGROUP caches, could it make sense to duplicate those as well? Otherwise we
could add a branch like:

if (gfp_flags & __GFP_DMA)
	/* use the global dma kmalloc caches */

> 
> >  }
> >  
> >  /*
> > @@ -634,7 +637,7 @@ static void *kmalloc_reserve(unsigned int *size, gfp_t flags, int node,
> >  	 * Try a regular allocation, when that fails and we're not entitled
> >  	 * to the reserves, fail.
> >  	 */
> > -	obj = kmalloc_node_track_caller(obj_size,
> > +	obj = kmem_buckets_alloc_node_track_caller(skb_data_buckets, obj_size,
> >  					flags | __GFP_NOMEMALLOC | __GFP_NOWARN,
> >  					node);
> 
> Minor nit: checkpatch laments WRT brackets alignment.

Will fix, thanks.

-- 
Pedro