On Thu, Sep 24, 2020 at 01:19:07PM +0200, Peter Zijlstra wrote: > On Thu, Sep 24, 2020 at 10:16:14AM +0200, Uladzislau Rezki wrote: > > The key point is "enough". We need pages to make a) fast progress b) support > > single argument of kvfree_rcu(one_arg). Not vice versa. That "enough" depends > > on scheduler latency and vague pre-allocated number of pages, it might > > be not enough what would require to refill it more and more or we can overshoot > > that would lead to memory overhead. So we have here timing issues and > > not accurate model. IMHO. > > I'm firmly opposed to the single argument kvfree_rcu() idea, that's > requiring memory to free memory. Not quite. First, there is a fallback when memory allocation fails. Second, in heavy-use situations, there is only one allocation per about 500 kvfree_rcu() calls on 64-bit systems. Third, there are other long-standing situations that require allocating memory in order to free memory. So I agree that it is a good general rule of thumb to avoid allocating on free paths, but there are exceptions. This is one of them. Thanx, Paul
