linux-kernel - Re: [PATCH 2/2 v2] sched/wait: Introduce lock breaker in wake_up_page

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Date:   Tue, 29 Aug 2017 09:01:11 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     "Liang, Kan" <kan.liang@...el.com>
Cc:     Tim Chen <tim.c.chen@...ux.intel.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...e.hu>, Andi Kleen <ak@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>, Jan Kara <jack@...e.cz>,
        Christopher Lameter <cl@...ux.com>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        linux-mm <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2 v2] sched/wait: Introduce lock breaker in wake_up_page_bit

On Tue, Aug 29, 2017 at 5:57 AM, Liang, Kan <kan.liang@...el.com> wrote:
>>
>> Attached is an ALMOST COMPLETELY UNTESTED forward-port of those two
>> patches, now without that nasty WQ_FLAG_ARRIVALS logic, because we now
>> always put the new entries at the end of the waitqueue.
>
> The patches fix the long wait issue.
>
> Tested-by: Kan Liang <kan.liang@...el.com>

Ok. I'm not 100% comfortable applying them at rc7, so let me think
about it. There's only one known load triggering this, and by "known"
I mean "not really known" since we don't even know what the heck it
does outside of intel and whoever your customer is.

So I suspect I'll apply the patches next merge window, and we can
maybe mark them for stable if this actually ends up mattering.

Can you tell if the problem is actually hitting _production_ use or
was some kind of benchmark stress-test?

               Linus