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Message-ID: <baa235a3-59c4-420e-8f1e-40c8526f3bf2@kernel.org>
Date: Wed, 22 Apr 2026 16:41:19 +0200
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Subject: Re: [PATCH 1/8] mm/slab: introduce k[v]free_rcu() with struct rcu_ptr
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To: "Harry Yoo (Oracle)" <harry@kernel.org>,
 Andrew Morton <akpm@linux-foundation.org>
Cc: Christoph Lameter <cl@gentwo.org>, David Rientjes <rientjes@google.com>,
 Roman Gushchin <roman.gushchin@linux.dev>, Hao Li <hao.li@linux.dev>,
 Alexei Starovoitov <ast@kernel.org>, Uladzislau Rezki <urezki@gmail.com>,
 "Paul E . McKenney" <paulmck@kernel.org>,
 Frederic Weisbecker <frederic@kernel.org>,
 Neeraj Upadhyay <neeraj.upadhyay@kernel.org>,
 Joel Fernandes <joelagnelf@nvidia.com>, Josh Triplett
 <josh@joshtriplett.org>, Boqun Feng <boqun@kernel.org>,
 Zqiang <qiang.zhang@linux.dev>, Steven Rostedt <rostedt@goodmis.org>,
 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
 Lai Jiangshan <jiangshanlai@gmail.com>, rcu@vger.kernel.org,
 linux-mm@kvack.org
References: <20260416091022.36823-1-harry@kernel.org>
 <20260416091022.36823-2-harry@kernel.org>
From: "Vlastimil Babka (SUSE)" <vbabka@kernel.org>
In-Reply-To: <20260416091022.36823-2-harry@kernel.org>
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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.