On Thu, Mar 12, 2020 at 11:11:38AM -0700, Paul E. McKenney wrote: > On Thu, Mar 12, 2020 at 04:27:30PM +0000, George Spelvin wrote: > > kvfree() is a superset of kfree(), so there's nothing obvious stopping > > kfree_rcu() from simply changing to kvfree() and everything will keep > > working. > > > > I'd probably add a kvfree_rcu() alias, just for documentation's sake and > > to make code that depends on the new feature explode at compile time, but > > it could be identical behind the scenes. > > > > There's an existing user in mm/list_lru.c already. > > > > I was just thinking of using kvmalloc() in a module, and realized that the > > lack of a core kvfree_rcu() helper meant I'd have to synchronize_rcu() on > > module unload. > > There was a recent proposal to do just that, but current patches in -rcu > use kfree_bulk(). It doesn't look to me that this works for kfvree() > under the covers in its current form. Could it be upgraded to handle > this case? > > Adding Vlad on CC for his thoughts. > Paul, see below my view: Answering to topic's question it looks like we need kvfree_rcu() support :) It is easy to add it actually. But if we are talking about the case when an object has rcu_head inside. From the other hand recent discussion showed that we would like to have head-less variant of the kvfree_rcu() functionality: https://lkml.org/lkml/2020/2/18/566 for example, as Ted pointed, he would go with head-less case(for ext4) only. The reason is nobody wants to modify internal structures injecting rcu_head there. Also there are many other places in the kernel where it would be good to have kfree_rcu() head-less variant as well. I spent some time implementing it together with Joel. It is ready from my side but only for RCU-tree case. Next step is RCU-tiny support, so i am working on it. I can send out an RFC for RCU-tree only support, so we can discuss it and agree on how to move forward. After that i or Joel or together can update RCU-tine. Joel: What do you think? Another thought. We can add kvfree_rcu(ptr, rcu) first, because it is easy and after that implement head-less case. -- Vlad Rezki
