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, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, 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 496B5C31E44 for ; Wed, 12 Jun 2019 01:09:48 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 14D0420874 for ; Wed, 12 Jun 2019 01:09:47 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="gAjfSlHu" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 14D0420874 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 89C896B026B; Tue, 11 Jun 2019 21:09:47 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 8267F6B026C; Tue, 11 Jun 2019 21:09:47 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 69F1F6B026D; Tue, 11 Jun 2019 21:09:47 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from mail-lf1-f71.google.com (mail-lf1-f71.google.com [209.85.167.71]) by kanga.kvack.org (Postfix) with ESMTP id 023806B026B for ; Tue, 11 Jun 2019 21:09:47 -0400 (EDT) Received: by mail-lf1-f71.google.com with SMTP id j27so2260964lfh.4 for ; Tue, 11 Jun 2019 18:09:46 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:dkim-signature:mime-version:references :in-reply-to:from:date:message-id:subject:to:cc; bh=SZXVeOYEeW/t6moRL6yl166/GZV1HqW8qo9aOqBVN+Q=; b=JXa6/LOZu5pnVKGnh+11gQN6Zo0gFD1g7fWocvtA5xhmYhl24cg1lx7vsmpcgLpN4w m56td4sgxWr88TcPd82AOqzJJbk8M38F90/LbsqiZW7Bf+rNZkCNbpRV8QAbD72csh23 b5X9VwxekqcU7k3Lbz5ypc5wFJ4U8ksCi589JZMF81WjRtr2uLvUHPjDhRhUVo4R0ssM hj9sj5ufjRhu83M2ltozRmfZYRrwBCun3cPeyzFW4TvGcAHOYNRLkpa5RIHpxhEB8iXT PTnLsTZuV+wSwrxqqIriUAxrm/ZGycwwbZavFFYmO3VjlGhXecZ95nZXG/1id3MYjsoS UZKQ== X-Gm-Message-State: APjAAAV04lSqGpP/+PaaDz5g1+qYRc+w83lSh1CTaxJNI0dA61uyrf6O jbHLcw3Y0lNITySihvMYDY/Qn8kJqnB6tNpPexR62Cu45Wli3aFuQUtBAp0r5r0yo2OaztdBt1P 0wZvK6btvjMUJs55hot3jfnOrxr+rYYC6byGZsER8V3FcxTifXr9RLWgZ8pnUNhQzYg== X-Received: by 2002:a19:f506:: with SMTP id j6mr15102852lfb.168.1560301786168; Tue, 11 Jun 2019 18:09:46 -0700 (PDT) X-Received: by 2002:a19:f506:: with SMTP id j6mr15102818lfb.168.1560301785236; Tue, 11 Jun 2019 18:09:45 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1560301785; cv=none; d=google.com; s=arc-20160816; b=dLPsTTeLLJPvqTUnCr839/ipyOgWLTFV7dAxSI7E+Arg56T8GxaYwuJMD1LHjDHMj6 UeU+wFtZVXMkAA37m4ii5rmyiWSrCQpNhu0lMn8x1gvBr0VNFyls3QjPEQFT7O9bmx6u afiu2ItKuzh9UU2mI+A70bP2PC3zQfvNlrh+cF4AB2VmoGBNNMwO6sfCP63uYbIXcBla FCgLOqJT2QzpCtkgn5EPyeTU6S6SipiOdWZVLZtKFPZrDus2hdAOHPXb1WGbayjWbirf p44Y9lIFEo6u4kT58sB03Ia2tICX2Gn7XTHMVN0uhrZVwWzpGBuIwSR8vDXviGSry+ME p2+w== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:dkim-signature; bh=SZXVeOYEeW/t6moRL6yl166/GZV1HqW8qo9aOqBVN+Q=; b=T+KDKXTOdXHcwqIsFsAUwQQiZPniznYgComYRIiVyVe808bwip6wXb8HQQPtLYP2+S Yi2lU4hIUHEx2ynDGqccbxyGUSb4iA8gT6jPLnIsy4LN+R13NKzTQXafcIf9gBeboBCN 590VZ2v66xC9oU80MInoj9WJNWnSWEoBJ1aZnCUuotZoW6UYg3e41ZOvYCsr3vu8tENw v+7wzvaQADJ2yVf9TW5prtPLh8FW/qHdc6C1FmQicLt9vrLaMkCxi+1KTA4kjcTgvQqP hq7PD9R1gWWKDGukQMa7O3j8Ym+EoK250okLz1aQ53X+1vEJSnFgv8VBfWFQmPaq9tOf Wglg== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@linux-foundation.org header.s=google header.b=gAjfSlHu; spf=pass (google.com: domain of torvalds@linuxfoundation.org designates 209.85.220.65 as permitted sender) smtp.mailfrom=torvalds@linuxfoundation.org Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id z6sor8731356ljk.17.2019.06.11.18.09.45 for (Google Transport Security); Tue, 11 Jun 2019 18:09:45 -0700 (PDT) Received-SPF: pass (google.com: domain of torvalds@linuxfoundation.org designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@linux-foundation.org header.s=google header.b=gAjfSlHu; spf=pass (google.com: domain of torvalds@linuxfoundation.org designates 209.85.220.65 as permitted sender) smtp.mailfrom=torvalds@linuxfoundation.org DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=SZXVeOYEeW/t6moRL6yl166/GZV1HqW8qo9aOqBVN+Q=; b=gAjfSlHuLsIpxvb8lF0RyxQXzEhYSHQJnAZ4as99A8GBRPKGt8LtILDEijhajNv2fV FXhIx40OUX4WPq1W1eQvis0UNqIoFt7tkihxVZ4QyREYOfVPuleZ/0Zq1i4TWCfQY/NA AhmvmJi02EHwj98eCflp9T4F3Jku2HpzQgXkw= X-Google-Smtp-Source: APXvYqzUMCAb3sGveCpRgIuq7hlU4dtuGeGQ4uaCcoXuElosX+7dR9MrIMxYytuZz5i0EkbJy6NqmQ== X-Received: by 2002:a05:651c:150:: with SMTP id c16mr134667ljd.193.1560301784353; Tue, 11 Jun 2019 18:09:44 -0700 (PDT) Received: from mail-lf1-f48.google.com (mail-lf1-f48.google.com. [209.85.167.48]) by smtp.gmail.com with ESMTPSA id f16sm3405810lfc.81.2019.06.11.18.09.40 for (version=TLS1_3 cipher=AEAD-AES128-GCM-SHA256 bits=128/128); Tue, 11 Jun 2019 18:09:41 -0700 (PDT) Received: by mail-lf1-f48.google.com with SMTP id z15so8008427lfh.13 for ; Tue, 11 Jun 2019 18:09:40 -0700 (PDT) X-Received: by 2002:ac2:50c4:: with SMTP id h4mr26185312lfm.61.1560301780325; Tue, 11 Jun 2019 18:09:40 -0700 (PDT) MIME-Version: 1.0 References: <20190611144102.8848-1-hch@lst.de> <20190611144102.8848-17-hch@lst.de> <1560300464.nijubslu3h.astroid@bobo.none> In-Reply-To: <1560300464.nijubslu3h.astroid@bobo.none> From: Linus Torvalds Date: Tue, 11 Jun 2019 15:09:24 -1000 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 16/16] mm: pass get_user_pages_fast iterator arguments in a structure To: Nicholas Piggin Cc: Rich Felker , "David S. Miller" , Christoph Hellwig , James Hogan , Paul Burton , Yoshinori Sato , Andrey Konovalov , Benjamin Herrenschmidt , Khalid Aziz , Linux List Kernel Mailing , linux-mips@vger.kernel.org, Linux-MM , linuxppc-dev@lists.ozlabs.org, Linux-sh list , Michael Ellerman , Paul Mackerras , sparclinux@vger.kernel.org, "the arch/x86 maintainers" Content-Type: text/plain; charset="UTF-8" X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Jun 11, 2019 at 2:55 PM Nicholas Piggin wrote: > > What does this do for performance? I've found this pattern can be > bad for store aliasing detection. I wouldn't expect it to be noticeable, and the lack of argument reloading etc should make up for it. Plus inlining makes it a non-issue when that happens. But I guess we could also at least look at using "restrict", if that ends up helping. Unlike the completely bogus type-based aliasing rules (that we disable because I think the C people were on some bad bad drugs when they came up with them), restricted pointers are a real thing that makes sense. That said, we haven't traditionally used it, and I don't know how much it helps gcc. Maybe gcc ignores it entirely? S Linus