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From:   Uladzislau Rezki <urezki@gmail.com>
Date:   Fri, 24 Apr 2020 14:28:35 +0200
To:     Joel Fernandes <joel@joelfernandes.org>
Cc:     Uladzislau Rezki <urezki@gmail.com>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Josh Triplett <josh@joshtriplett.org>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        rcu <rcu@vger.kernel.org>, Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH RFC] rcu/tree: Refactor object allocation and try harder
 for array allocation
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> 
> I think Johannes said that waking up kswapd is Ok. OTOH, I did not see
> the drawback in waking up kswapd to do background reclaim since it
> does not happen synchronously right? I think Johannes said we can do
> better than just waking kswapd by also doing light direct reclaim
> using __GFP_NORETRY but let me know if I missed something.
> 
Then i misunderstood that point. So, seems it is settled now. We just
use GFP_NOWAIT | __GFP_RECLAIM | __GFP_NORETRY | __GFP_NOWARN for headless
case, i.e. when we can sleep. It will do direct reclaim(slow path), but
light one because of __GFP_NORETRY.

Does it sound good?

> > For single argument we inline freeing into current context after
> > synchronize_rcu() because it follows might_sleep() annotation.
> 
> Yes.
> 
> Also, with the additional caching being planned, we could avoid the
> chances of hitting the synchronize_rcu inlining.
> 
Or minimize it.

There is also one question i would like to clarify. That is dynamic head
attaching that requires small allocations. Do we drop it?

Thanks!

--
Vlad Rezki