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=-4.1 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no 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 516EBC433E7 for ; Wed, 2 Sep 2020 20:13:59 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 12A5F2083B for ; Wed, 2 Sep 2020 20:13:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=ziepe.ca header.i=@ziepe.ca header.b="Qwf6X/kG" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 12A5F2083B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ziepe.ca Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 96838900019; Wed, 2 Sep 2020 16:13:58 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 918C290000F; Wed, 2 Sep 2020 16:13:58 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 8078B900019; Wed, 2 Sep 2020 16:13:58 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0173.hostedemail.com [216.40.44.173]) by kanga.kvack.org (Postfix) with ESMTP id 6868B90000F for ; Wed, 2 Sep 2020 16:13:58 -0400 (EDT) Received: from smtpin01.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 10BCB180AD806 for ; Wed, 2 Sep 2020 20:13:58 +0000 (UTC) X-FDA: 77219222556.01.trade57_060017a270a3 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin01.hostedemail.com (Postfix) with ESMTP id D79E410049A5E for ; Wed, 2 Sep 2020 20:13:57 +0000 (UTC) X-HE-Tag: trade57_060017a270a3 X-Filterd-Recvd-Size: 4278 Received: from mail-qk1-f193.google.com (mail-qk1-f193.google.com [209.85.222.193]) by imf36.hostedemail.com (Postfix) with ESMTP for ; Wed, 2 Sep 2020 20:13:57 +0000 (UTC) Received: by mail-qk1-f193.google.com with SMTP id u3so946629qkd.9 for ; Wed, 02 Sep 2020 13:13:57 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ziepe.ca; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=VtKLlAudRnA2vKDoZNQw5csEIPXvQwIKm3VyTbaIKFY=; b=Qwf6X/kGgSmY9tKp7Kmk3c8MgxIjvqFpEQAe+tb1+XOXXgvyehDPKeYG7dZ/Yg3IX6 htTDkWFcqvo513Hi/a7qgs846lJoqXVAXRLY91hdU61Y6OJwM73W0pMKYYASAJzRG86+ Dg/4lQzFDbgl69fZkKJw7LZwiwF3cwnrxKfHjCVxdDezuLssdPD1RCUPY998/GHXvD66 vXdCC47ctdTSW43mZLLck7PEVdwrveAum6OrxzF6kuLEFcjT+1LtRvd1cwQbcz8kXeCO 1YqtVf246V4JoEYZACerGXbT/EI/gGjAeg6BCbC2etnr610vhlV/2Mf9s7fG3C/sl3Zf cwzw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=VtKLlAudRnA2vKDoZNQw5csEIPXvQwIKm3VyTbaIKFY=; b=q7BGvzNbllWwjm4ye2gxCA9KENxcLAaZykhLsMWVkR37gvQjftp5lCdVCHTaz2ZhNn Re3wDX46A8SkMnaISvyKKl6Xh8v23Xmc8mbtpffwvayhcC7hqrTUj9/xMHvfY45qCm2+ 3EeLmycA6DP5ymPJZ+KJf0BUq0WcY5zTE4fetVEC+l+smAi8ybjjWFHOrAR8OITGsynv BVVQDgZhvaph6KATFn3t+ZWdSSlucaeuaUKGhzczSKPBMtX0mopMslFQWvt8YpImUBBT 1djRH4jSThKc8EkqgSXHOCpAx3ne4h4nysyx0UmfZyvEs4u4hZVCzgmuDWa4CHdd8/OG i7vg== X-Gm-Message-State: AOAM531/Bgt7AR4C7BNjCsJ/0ynRipPQ0ZEuFNMSQSi7TPM33qyFK942 k26MsaZ2j/pdy1m58ZMy3IOSqw== X-Google-Smtp-Source: ABdhPJxP9sYQMnp7dADWRBTcdNFumTmUhJGfW+FF9H/GSd4vNcNPJ3p18WOwE1ej6gXtP23Bzcc3NA== X-Received: by 2002:a37:a484:: with SMTP id n126mr8834583qke.5.1599077636904; Wed, 02 Sep 2020 13:13:56 -0700 (PDT) Received: from ziepe.ca (hlfxns017vw-156-34-48-30.dhcp-dynamic.fibreop.ns.bellaliant.net. [156.34.48.30]) by smtp.gmail.com with ESMTPSA id g18sm347980qtu.69.2020.09.02.13.13.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 02 Sep 2020 13:13:56 -0700 (PDT) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1kDZ8l-0068s3-Em; Wed, 02 Sep 2020 17:13:55 -0300 Date: Wed, 2 Sep 2020 17:13:55 -0300 From: Jason Gunthorpe To: Gerald Schaefer Cc: John Hubbard , Andrew Morton , Christian Borntraeger , Linus Torvalds , linux-mm , LKML , Vasily Gorbik , Alexander Gordeev , linux-s390@vger.kernel.org, Heiko Carstens , Claudio Imbrenda Subject: Re: [RFC PATCH 0/2] mm/gup: fix gup_fast with dynamic page table folding Message-ID: <20200902201355.GJ24045@ziepe.ca> References: <20200828140314.8556-1-gerald.schaefer@linux.ibm.com> <9071c9fa-ba6a-90dc-2d7a-8b155141d890@de.ibm.com> <20200831121553.8be5dcdbdbc5256846ac513e@linux-foundation.org> <20200901194020.418da486@thinkpad> <91988792-069c-31a6-7840-0122357538c7@nvidia.com> <20200902142437.5f39b4bb@thinkpad> <20200902170958.09be0c3e@thinkpad> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200902170958.09be0c3e@thinkpad> X-Rspamd-Queue-Id: D79E410049A5E X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam03 X-Bogosity: Ham, tests=bogofilter, spamicity=0.015627, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Sep 02, 2020 at 05:09:58PM +0200, Gerald Schaefer wrote: > I guess we *could* assume that all the extra pXd_offset() calls and > also the de-referencing would be optimized out by the compiler for other > archs, but it is one example where my gut tells me that this might not > be so trivial and w/o unwanted effects after all. Assigning to a variable that is never read should be eliminated.. If things are very complex then the pXX_offset function might need to be marked with attribute pure, but I think this should be reliable? Jason