> > Yes, I mean __GFP_MEMALLOC. Sorry, the patch was just to show the idea and > marked as RFC. > > Good point on the atomic aspect of this path, you are right we cannot sleep. > I believe the GFP_NOWAIT I mentioned in my last reply will take care of that? > I think there should be GFP_ATOMIC used, because it has more chance to return memory then GFP_NOWAIT. I see that Michal has same view on it. > > As for removing __GFP_NOWARN. Actually it is expectable that an > > allocation can fail, if so we follow last emergency case. You > > can see the trace but what would you do with that information? > > Yes, the benefit of the trace/warning is that the user can switch to a > non-headless API and avoid the synchronize_rcu(), that would help them get > faster kfree_rcu() performance instead of having silent slowdowns. > Agree. What about just adding WARN_ON_ONCE()? I am just thinking if it could be harmful or not. > > It also tells us whether the headless API is worth it in the long run, I > think it is worth it because we will likely never hit the synchronize_rcu() > failsafe. But if we hit it a lot, at least it wont happen silently. > Agree. > Paul was concerned about following scenario with hitting synchronize_rcu(): > 1. Consider a system under memory pressure. > 2. Consider some other subsystem X depending on another system Y which uses > kfree_rcu(). If Y doesn't complete the operation in time, X accumulates > more memory. > 3. Since kfree_rcu() on Y hits synchronize_rcu() a lot, it slows it down. > This causes X to further allocate memory, further causing a chain > reaction. > Paul, please correct me if I'm wrong. > I see your point and agree that in theory it can happen. So, we should make it more tight when it comes to rcu_head attachment logic. -- Vlad Rezki
