From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1752575AbdHVTzm (ORCPT <rfc822;w@1wt.eu>);
        Tue, 22 Aug 2017 15:55:42 -0400
Received: from mga14.intel.com ([192.55.52.115]:48781 "EHLO mga14.intel.com"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S1751768AbdHVTzk (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
        Tue, 22 Aug 2017 15:55:40 -0400
X-ExtLoop1: 1
X-IronPort-AV: E=Sophos;i="5.41,413,1498546800"; 
   d="scan'208";a="303233670"
From: "Liang, Kan" <kan.liang@intel.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
CC: Mel Gorman <mgorman@techsingularity.net>, Mel Gorman <mgorman@suse.de>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        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>,
        linux-mm <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH 1/2] sched/wait: Break up long wake list walk
Thread-Topic: [PATCH 1/2] sched/wait: Break up long wake list walk
Thread-Index: AQHTFWNBYSKZKyu5OE6Y+fM96SxNwqKEIDEAgASaOPD//398AIAAsKCA//+X4wCAAQZZgIAAplUA//+BiwAAFSW90P//ia2AgAASl4CAAAVjAIAEq10A//91k2D//XJ4kIAEpo4A//9gzkA=
Date: Tue, 22 Aug 2017 19:55:37 +0000
Message-ID: <37D7C6CF3E00A74B8858931C1DB2F0775378A377@SHSMSX103.ccr.corp.intel.com>
References: <CA+55aFwzTMrZwh7TE_VeZt8gx5Syoop-kA=Xqs56=FkyakrM6g@mail.gmail.com>
 <37D7C6CF3E00A74B8858931C1DB2F0775378761B@SHSMSX103.ccr.corp.intel.com>
 <CA+55aFy_RNx5TQ8esjPPOKuW-o+fXbZgWapau2MHyexcAZtqsw@mail.gmail.com>
 <20170818122339.24grcbzyhnzmr4qw@techsingularity.net>
 <37D7C6CF3E00A74B8858931C1DB2F077537879BB@SHSMSX103.ccr.corp.intel.com>
 <20170818144622.oabozle26hasg5yo@techsingularity.net>
 <37D7C6CF3E00A74B8858931C1DB2F07753787AE4@SHSMSX103.ccr.corp.intel.com>
 <CA+55aFxZjjqUM4kPvNEeZahPovBHFATiwADj-iPTDN0-jnU67Q@mail.gmail.com>
 <20170818185455.qol3st2nynfa47yc@techsingularity.net>
 <CA+55aFwX0yrUPULrDxTWVCg5c6DKh-yCG84NXVxaptXNQ4O_kA@mail.gmail.com>
 <20170821183234.kzennaaw2zt2rbwz@techsingularity.net>
 <37D7C6CF3E00A74B8858931C1DB2F07753788B58@SHSMSX103.ccr.corp.intel.com>
 <37D7C6CF3E00A74B8858931C1DB2F0775378A24A@SHSMSX103.ccr.corp.intel.com>
 <CA+55aFy=4y0fq9nL2WR1x8vwzJrDOdv++r036LXpR=6Jx8jpzg@mail.gmail.com>
In-Reply-To: <CA+55aFy=4y0fq9nL2WR1x8vwzJrDOdv++r036LXpR=6Jx8jpzg@mail.gmail.com>
Accept-Language: zh-CN, en-US
Content-Language: en-US
X-MS-Has-Attach: 
X-MS-TNEF-Correlator: 
x-titus-metadata-40: eyJDYXRlZ29yeUxhYmVscyI6IiIsIk1ldGFkYXRhIjp7Im5zIjoiaHR0cDpcL1wvd3d3LnRpdHVzLmNvbVwvbnNcL0ludGVsMyIsImlkIjoiOTM2YTBlMWMtOTBhMC00NTU5LWJhYjktYWM2YTk5N2YwOTJkIiwicHJvcHMiOlt7Im4iOiJDVFBDbGFzc2lmaWNhdGlvbiIsInZhbHMiOlt7InZhbHVlIjoiQ1RQX0lDIn1dfV19LCJTdWJqZWN0TGFiZWxzIjpbXSwiVE1DVmVyc2lvbiI6IjE2LjUuOS4zIiwiVHJ1c3RlZExhYmVsSGFzaCI6Ino4cVJpRjl2RFVFU2dCRTdqRXBHbHFGek4wc0lXTHpMcjZCZEhLZmx2Qnc9In0=
x-ctpclassification: CTP_IC
dlp-product: dlpe-windows
dlp-version: 10.0.102.7
dlp-reaction: no-action
x-originating-ip: [10.239.127.40]
Content-Type: text/plain; charset="utf-8"
MIME-Version: 1.0
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Transfer-Encoding: 8bit
X-MIME-Autoconverted: from base64 to 8bit by nfs id v7MJtlsb016756

 
> So I propose testing the attached trivial patch. 

It doesn’t work. 
The call stack is the same.

   100.00%  (ffffffff821af140)
            |
            ---wait_on_page_bit
               __migration_entry_wait
               migration_entry_wait
               do_swap_page
               __handle_mm_fault
               handle_mm_fault
               __do_page_fault
               do_page_fault
               page_fault
               |
               |--40.62%--0x123a2
               |          start_thread
               |


> It may not do anything at all.
> But the existing code is actually doing extra work just to be fragile, in case the
> scenario above can happen.
> 
> Comments?
> 
>                 Linus