From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.9 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 62FF4C65BAE for ; Thu, 13 Dec 2018 15:56:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1FA0720879 for ; Thu, 13 Dec 2018 15:56:08 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=amazonses.com header.i=@amazonses.com header.b="QHf/o7fZ" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1FA0720879 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728915AbeLMP4H (ORCPT ); Thu, 13 Dec 2018 10:56:07 -0500 Received: from a9-114.smtp-out.amazonses.com ([54.240.9.114]:43172 "EHLO a9-114.smtp-out.amazonses.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727707AbeLMP4G (ORCPT ); Thu, 13 Dec 2018 10:56:06 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/simple; s=ug7nbtf4gccmlpwj322ax3p6ow6yfsug; d=amazonses.com; t=1544716565; h=Date:From:To:cc:Subject:In-Reply-To:Message-ID:References:MIME-Version:Content-Type:Feedback-ID; bh=NZabmP3XK9/5WAKKWC7R595/zGK/oTVP2WOhqXoEXqg=; b=QHf/o7fZT9OJhhJg0RiOZNIi1yEGSh+sOyZp8rZgM1JekqaNoGoZSvpLHkw3OvJj lQZwiM31jeFJTqYMBRSmMMff0XR/AlcyAibWiNbD68JjdPgOKCvcP6cuvQuqsrBo+Pe HyW2PcOPBsR2AXeE4WjYHRMC1+/efbtvRSoSUXDg= Date: Thu, 13 Dec 2018 15:56:05 +0000 From: Christopher Lameter X-X-Sender: cl@nuc-kabylake To: Jerome Glisse cc: Dave Chinner , Jan Kara , John Hubbard , Matthew Wilcox , Dan Williams , John Hubbard , Andrew Morton , Linux MM , tom@talpey.com, Al Viro , benve@cisco.com, Christoph Hellwig , "Dalessandro, Dennis" , Doug Ledford , Jason Gunthorpe , Michal Hocko , mike.marciniszyn@intel.com, rcampbell@nvidia.com, Linux Kernel Mailing List , linux-fsdevel Subject: Re: [PATCH 1/2] mm: introduce put_user_page*(), placeholder versions In-Reply-To: <20181213020229.GN5037@redhat.com> Message-ID: <01000167a8483bd2-16ae0d3e-d217-4993-a80a-25d221c677e4-000000@email.amazonses.com> References: <59ca5c4b-fd5b-1fc6-f891-c7986d91908e@nvidia.com> <7b4733be-13d3-c790-ff1b-ac51b505e9a6@nvidia.com> <20181207191620.GD3293@redhat.com> <3c4d46c0-aced-f96f-1bf3-725d02f11b60@nvidia.com> <20181208022445.GA7024@redhat.com> <20181210102846.GC29289@quack2.suse.cz> <20181212150319.GA3432@redhat.com> <20181212214641.GB29416@dastard> <20181212215931.GG5037@redhat.com> <20181213005119.GD29416@dastard> <20181213020229.GN5037@redhat.com> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-SES-Outgoing: 2018.12.13-54.240.9.114 Feedback-ID: 1.us-east-1.fQZZZ0Xtj2+TD7V5apTT/NrT6QKuPgzCT/IC7XYgDKI=:AmazonSES Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 12 Dec 2018, Jerome Glisse wrote: > On Thu, Dec 13, 2018 at 11:51:19AM +1100, Dave Chinner wrote: > > > > > [O1] Avoid write back from a page still being written by either a > > > > > device or some direct I/O or any other existing user of GUP. > > > > IOWs, you need to mark pages being written to by a GUP as > > PageWriteback, so all attempts to write the page will block on > > wait_on_page_writeback() before trying to write the dirty page. > > No you don't and you can't for the simple reasons is that the GUP > of some device driver can last days, weeks, months, years ... so > it is not something you want to do. Here is what happens today: I think it would be better to use the established way to block access that Dave suggests. Maybe deal with the issue of threads being blocked for a long time instead? Introduce a way to abort these attempts in a controlled fashion that also allows easy debugging of these conflicts?