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=-4.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 2E745C4338F for ; Sat, 7 Aug 2021 10:31:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0CD3460E78 for ; Sat, 7 Aug 2021 10:31:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231897AbhHGKbi (ORCPT ); Sat, 7 Aug 2021 06:31:38 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40992 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231687AbhHGKbg (ORCPT ); Sat, 7 Aug 2021 06:31:36 -0400 Received: from mail-wr1-x429.google.com (mail-wr1-x429.google.com [IPv6:2a00:1450:4864:20::429]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 41C9FC0613CF; Sat, 7 Aug 2021 03:31:18 -0700 (PDT) Received: by mail-wr1-x429.google.com with SMTP id n12so4366957wrr.2; Sat, 07 Aug 2021 03:31:18 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=to:cc:references:from:subject:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=Xz2POERoj03wWLZEE/kDhO0wJ4yd+zaF3oDDbK7OnvA=; b=H2XHvma4LuuSVfBN8ILh6Jp9Pdbm1fXiqibs3HZAbEsSl2t9PmxV++zAVQc3H20S1J o7IRX3aQFf4Hu51bxL2+rQoDOmUElyxC+/cv9kq6OOirBn306UgSQNktK80MTV/7ewUD flytjI+yKhudqqDhG2ZblB/OFBenWkx8apuISOGUkeLkgSL9Dk+ZBZ57FLYTNxlkdHQ/ wCoYiIZCpQj7SN/bW7GPLxUa5EaB5nnfsqBeo3DxPgM8nut6+YKOzpcH1Yy95NBXBwRa r9NXjx4m/j24gIPdtchs4FlDitXBdMrojfpcAUPa0E8SECt6Y5zx3h872RH2NCDAHhdk zDDw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:to:cc:references:from:subject:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=Xz2POERoj03wWLZEE/kDhO0wJ4yd+zaF3oDDbK7OnvA=; b=p5CE2Jzdhcw5ZaTEdsdxaVB4yeDgSj0+1D81NFNFe8cgvCbf48UIv0F+sVg+Mnuusi /BV5rVEh3ib5rlCMsj8iLum+ivOjuNQL7JxO2tAfmcqt7fbQQTjzBD2TsHItN1hW2oHd 2tSofvG9gfOi8rm/r7vNaQzd+JvQosw4b6pN1ThpgBLHOBvDfC2FzDEs+7DPrNpHW459 9muJue30eOwg4WalpCPAZnooTuON6GeQ9OGeE+/AhmNTcI2jBOB6Q7mBAF2g8s7tD3gQ nx9ZCAqKp93/D7VUMmtLwETkaUdc3wOloy1OhRYLuLZmTdrjFxxW4twrfsSAp+wMuFo+ L8Cg== X-Gm-Message-State: AOAM5322jGOM5+lU3T3aEE1LA2743uyUdudjTI+O0QDEE0RzBA16Egjv daB8ywfT40rcN9IPePCi/4kQzpVA45Y= X-Google-Smtp-Source: ABdhPJzaxfdJrn/5/vNvO8eZMGRSq0NWEnWYnVHGVQv3O4xWrSyYXv+bhW2iZXMYwhQQZTbFwvfGRQ== X-Received: by 2002:adf:f383:: with SMTP id m3mr14747988wro.81.1628332276733; Sat, 07 Aug 2021 03:31:16 -0700 (PDT) Received: from [192.168.8.197] ([85.255.237.206]) by smtp.gmail.com with ESMTPSA id x15sm15023813wmc.13.2021.08.07.03.31.15 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 07 Aug 2021 03:31:16 -0700 (PDT) To: Al Viro Cc: Andrew Morton , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Jens Axboe , linux-kernel@vger.kernel.org References: <07bd408d6cad95166b776911823b40044160b434.1628248975.git.asml.silence@gmail.com> From: Pavel Begunkov Subject: Re: [RFC] mm: optimise generic_file_read_iter Message-ID: Date: Sat, 7 Aug 2021 11:30:48 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.12.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/6/21 2:48 PM, Al Viro wrote: > On Fri, Aug 06, 2021 at 12:42:43PM +0100, Pavel Begunkov wrote: >> Unless direct I/O path of generic_file_read_iter() ended up with an >> error or a short read, it doesn't use inode. So, load inode and size >> later, only when they're needed. This cuts two memory reads and also >> imrpoves code generation, e.g. loads from stack. > > ... and the same question here. > >> NOTE: as a side effect, it reads inode->i_size after ->direct_IO(), and >> I'm not sure whether that's valid, so would be great to get feedback >> from someone who knows better. > > Ought to be safe, I think, but again, how much effect have you observed > from the patch? Answering for both patches -- I haven't benchmarked it and don't expect to find anything just from this one, considering variance between runs. I took a loot at the assembly (gcc 11.1), it removes 2 reads to get i_size, write+read that i_size from stack, because it stashed it on the stack. For example, we've squeezed several percents of throughput before on the io_uring side just by cutting sheer number of not too expensive individually instructions. IMHO, it's easier to do when you spotted something by the way, than rediscovering the same during a performance safari. -- Pavel Begunkov