From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f71.google.com (mail-oi0-f71.google.com [209.85.218.71]) by kanga.kvack.org (Postfix) with ESMTP id B869F2806EC for ; Tue, 22 Aug 2017 16:42:15 -0400 (EDT) Received: by mail-oi0-f71.google.com with SMTP id x21so5841532oif.1 for ; Tue, 22 Aug 2017 13:42:15 -0700 (PDT) Received: from mail-oi0-x22e.google.com (mail-oi0-x22e.google.com. [2607:f8b0:4003:c06::22e]) by mx.google.com with ESMTPS id l144si12225289oig.201.2017.08.22.13.42.14 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 22 Aug 2017 13:42:14 -0700 (PDT) Received: by mail-oi0-x22e.google.com with SMTP id f11so197728684oic.0 for ; Tue, 22 Aug 2017 13:42:14 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <37D7C6CF3E00A74B8858931C1DB2F0775378A377@SHSMSX103.ccr.corp.intel.com> References: <37D7C6CF3E00A74B8858931C1DB2F0775378761B@SHSMSX103.ccr.corp.intel.com> <20170818122339.24grcbzyhnzmr4qw@techsingularity.net> <37D7C6CF3E00A74B8858931C1DB2F077537879BB@SHSMSX103.ccr.corp.intel.com> <20170818144622.oabozle26hasg5yo@techsingularity.net> <37D7C6CF3E00A74B8858931C1DB2F07753787AE4@SHSMSX103.ccr.corp.intel.com> <20170818185455.qol3st2nynfa47yc@techsingularity.net> <20170821183234.kzennaaw2zt2rbwz@techsingularity.net> <37D7C6CF3E00A74B8858931C1DB2F07753788B58@SHSMSX103.ccr.corp.intel.com> <37D7C6CF3E00A74B8858931C1DB2F0775378A24A@SHSMSX103.ccr.corp.intel.com> <37D7C6CF3E00A74B8858931C1DB2F0775378A377@SHSMSX103.ccr.corp.intel.com> From: Linus Torvalds Date: Tue, 22 Aug 2017 13:42:13 -0700 Message-ID: Subject: Re: [PATCH 1/2] sched/wait: Break up long wake list walk Content-Type: multipart/mixed; boundary="001a113d3a32562b9405575da121" Sender: owner-linux-mm@kvack.org List-ID: To: "Liang, Kan" Cc: Mel Gorman , Mel Gorman , "Kirill A. Shutemov" , Tim Chen , Peter Zijlstra , Ingo Molnar , Andi Kleen , Andrew Morton , Johannes Weiner , Jan Kara , linux-mm , Linux Kernel Mailing List --001a113d3a32562b9405575da121 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Tue, Aug 22, 2017 at 12:55 PM, Liang, Kan wrote: > >> So I propose testing the attached trivial patch. > > It doesn=E2=80=99t work. > The call stack is the same. So I would have expected the stack trace to be the same, and I would even expect the CPU usage to be fairly similar, because you'd see repeating from the callers (taking the fault again if the page is - once again - being migrated). But I was hoping that the wait queues would be shorter because the loop for the retry would be bigger. Oh well. I'm slightly out of ideas. Apparently the yield() worked ok (apart from not catching all cases), and maybe we could do a version that waits on the page bit in the non-contended case, but yields under contention? IOW, maybe this is the best we can do for now? Introducing that "wait_on_page_migration()" helper might allow us to tweak this a bit as people come up with better ideas.. And then add Tim's patch for the general worst-case just in case? 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