Subject: Re: [PATCH 2/2 v2] sched/wait: Introduce lock breaker in
 wake_up_page_bit
To: Linus Torvalds <torvalds@linux-foundation.org>,
        "Liang, Kan" <kan.liang@intel.com>
Cc: Mel Gorman <mgorman@techsingularity.net>,
        Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@elte.hu>,
        Andi Kleen <ak@linux.intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Johannes Weiner <hannes@cmpxchg.org>, Jan Kara <jack@suse.cz>,
        Christopher Lameter <cl@linux.com>,
        "Eric W . Biederman" <ebiederm@xmission.com>,
        Davidlohr Bueso <dave@stgolabs.net>, linux-mm <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
References: <83f675ad385d67760da4b99cd95ee912ca7c0b44.1503677178.git.tim.c.chen@linux.intel.com>
 <cd8ce7fbca9c126f7f928b8fa48d7a9197955b45.1503677178.git.tim.c.chen@linux.intel.com>
 <CA+55aFyErsNw8bqTOCzcrarDZBdj+Ev=1N3sV-gxtLTH03bBFQ@mail.gmail.com>
 <f10f4c25-49c0-7ef5-55c2-769c8fd9bf90@linux.intel.com>
 <CA+55aFzNikMsuPAaExxT1Z8MfOeU6EhSn6UPDkkz-MRqamcemg@mail.gmail.com>
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 <37D7C6CF3E00A74B8858931C1DB2F077537A1C19@SHSMSX103.ccr.corp.intel.com>
 <CA+55aFwECeY-x=_du67qAxkta_0LeUw_BQA1kP337SBV3znN2Q@mail.gmail.com>
From: Tim Chen <tim.c.chen@linux.intel.com>
Message-ID: <bd2d09ea-47d1-c0a7-8d4d-604bb4bc28bc@linux.intel.com>
Date: Tue, 29 Aug 2017 09:13:29 -0700
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On 08/29/2017 09:01 AM, Linus Torvalds wrote:
> On Tue, Aug 29, 2017 at 5:57 AM, Liang, Kan <kan.liang@intel.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@intel.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?
> 
> 

It is affecting not a production use, but the customer's acceptance
test for their systems.  So I suspect it is a stress test.

Tim