Re: [PATCH 1/8] mm/slab: introduce k[v]free_rcu() with struct rcu_ptr

["Harry Yoo (Oracle)" <harry@kernel.org>]

On Wed, Apr 22, 2026 at 04:41:19PM +0200, Vlastimil Babka (SUSE) wrote:
> On 4/16/26 11:10, Harry Yoo (Oracle) wrote:
> > @@ -1523,18 +1522,34 @@ kvfree_rcu_bulk(struct kfree_rcu_cpu *krcp,
> >  }
> >  
> >  static void
> > -kvfree_rcu_list(struct rcu_head *head)
> > +kvfree_rcu_list(struct rcu_ptr *head)
> >  {
> > -	struct rcu_head *next;
> > +	struct rcu_ptr *next;
> >  
> >  	for (; head; head = next) {
> > -		void *ptr = (void *) head->func;
> > -		unsigned long offset = (void *) head - ptr;
> > +		void *ptr;
> > +		unsigned long offset;
> > +		struct slab *slab;
> >  
> > +		if (is_vmalloc_addr(head)) {
> > +			ptr = (void *)PAGE_ALIGN_DOWN((unsigned long)head);
> > +		} else {
> > +			slab = virt_to_slab(head);
> > +			if (!slab)
> > +				ptr = (void *)PAGE_ALIGN_DOWN((unsigned long)head);
> > +			else if (is_kfence_address(head))
> > +				ptr = kfence_object_start(head);
> > +			else
> > +				ptr = nearest_obj(slab->slab_cache, slab, head);
> > +		}
> 
> It seems a bit wasteful to do this... (especially the virt_to_slab()) part.
> 
> > +
> > +		offset = (void *)head - ptr;
> >  		next = head->next;
> >  		debug_rcu_head_unqueue((struct rcu_head *)ptr);
> >  		rcu_lock_acquire(&rcu_callback_map);
> > -		trace_rcu_invoke_kvfree_callback("slab", head, offset);
> > +		trace_rcu_invoke_kvfree_callback("slab",
> > +						(struct rcu_head *)head,
> > +						offset);
> >  
> >  		kvfree(ptr);
> 
> ... and then throw it all away and let kvfree(ptr) do it again. So maybe we
> could then call something more internal and specific based on the result of
> the above.

Good point, will do.

-- 
Cheers,
Harry / Hyeonggon