linux-kernel - Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink

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Message-ID: <20161130163820.GQ3092@twins.programming.kicks-ass.net>
Date:   Wed, 30 Nov 2016 17:38:20 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:     Michal Hocko <mhocko@...nel.org>,
        Donald Buczek <buczek@...gen.mpg.de>,
        Paul Menzel <pmenzel@...gen.mpg.de>, dvteam@...gen.mpg.de,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Josh Triplett <josh@...htriplett.org>
Subject: Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and
 `mem_cgroup_shrink_node`

On Wed, Nov 30, 2016 at 06:29:55AM -0800, Paul E. McKenney wrote:
> We can, and you are correct that cond_resched() does not unconditionally
> supply RCU quiescent states, and never has.  Last time I tried to add
> cond_resched_rcu_qs() semantics to cond_resched(), I got told "no",
> but perhaps it is time to try again.

Well, you got told: "ARRGH my benchmark goes all regress", or something
along those lines. Didn't we recently dig out those commits for some
reason or other?

Finding out what benchmark that was and running it against this patch
would make sense.

Also, I seem to have missed, why are we going through this again?