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=-2.2 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,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 7D1DBC433E1 for ; Thu, 9 Jul 2020 13:53:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 588102074B for ; Thu, 9 Jul 2020 13:53:12 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=kernel-dk.20150623.gappssmtp.com header.i=@kernel-dk.20150623.gappssmtp.com header.b="BjWZhcJG" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728025AbgGINxK (ORCPT ); Thu, 9 Jul 2020 09:53:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40986 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727950AbgGINxK (ORCPT ); Thu, 9 Jul 2020 09:53:10 -0400 Received: from mail-io1-xd43.google.com (mail-io1-xd43.google.com [IPv6:2607:f8b0:4864:20::d43]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 49785C08E6DC for ; Thu, 9 Jul 2020 06:53:10 -0700 (PDT) Received: by mail-io1-xd43.google.com with SMTP id k23so2343942iom.10 for ; Thu, 09 Jul 2020 06:53:10 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel-dk.20150623.gappssmtp.com; s=20150623; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=MdcBjmP7qGWR1MpBAxRS6pB+OY/RQLdcm4qT/nupz3g=; b=BjWZhcJGYeO/nZp2SRVBsmB5Ei77q8MrUISpXYS8soe+YNMxcSX6beIjMuI3Q05mxL gXY4Bw0kuYaA6GAj4ujXqufV5EipZgKw/jMhE5sCSyg9rMz64OM3LShd71rVSmg1N5ap /WH8FEF0+S2cFsHijeSnwEfnr6m/w8IkO0IUYeyKSmZA3K1VuSYheHIZc0bX4J+miskc s8hGdjjZJl4hLHqJ0RpwJ8bSXyqx7qO5aUtQg9kzDTIEpTDvUrAHjpbO0CVwFCvuc8+M MkAwSdB5SFIDB63Cth1qeUqZr5I+O4JOII0KIJ8lIg/eL3m9KP/hw51WcHviT92cRQky bimQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=MdcBjmP7qGWR1MpBAxRS6pB+OY/RQLdcm4qT/nupz3g=; b=iyMLltSlLeTbqxlNcDOK5D3JGq95MMDV5EFULQ5ZZU9iU+f1lGNjX5vWkprrMpQ+j+ ERZk+Z43YnQEAu9r3I+EMdzNJ4ZiaOJEIEAVZmQ31vx9as6iqilwtCEHtlo2T1xrkgk+ yViZODle91XJV3jETwaseOkaDqgqvqnAZn8B2O09ePM6N1Yn2WeWj6pKW9oRQxdLVZb/ qzUShFhp3Rq1SIMILAJRFjSwqrfPMr3qii41oiv1zAlqoKZiM0SYehUtpG8UvtyoIhiX beTJwrnXYivJtAr7itx1S9i3/BRxn8wlJQZ0KOUCSK3HBpbB50SaCc7E233jGoTx5MPZ goQw== X-Gm-Message-State: AOAM533KZZo5R502a2JnNx+vVpFQCBSczVKq8+JwEOOhUrv6obqJHTMA S6sGmw4I6DBYMZqzvuugZXK/eA== X-Google-Smtp-Source: ABdhPJy39Z382Q5bYeHMpva+0EOk6l7VKjY+mG3CJn9HtsoBPJfb2IFz340kCmDhMrghd/EAVUHtHQ== X-Received: by 2002:a02:c6a7:: with SMTP id o7mr74870852jan.7.1594302789510; Thu, 09 Jul 2020 06:53:09 -0700 (PDT) Received: from [192.168.1.58] ([65.144.74.34]) by smtp.gmail.com with ESMTPSA id 13sm1920029ilj.81.2020.07.09.06.53.08 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 09 Jul 2020 06:53:08 -0700 (PDT) Subject: Re: [PATCH 0/2] Remove kiocb ki_complete To: Matthew Wilcox , Christoph Hellwig Cc: linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-aio@kvack.org, io-uring@vger.kernel.org, linux-kernel@vger.kernel.org, Kanchan Joshi , Javier Gonzalez References: <20200708222637.23046-1-willy@infradead.org> <20200709101705.GA2095@infradead.org> <20200709111036.GA12769@casper.infradead.org> <20200709132611.GA1382@infradead.org> <20200709133249.GC12769@casper.infradead.org> From: Jens Axboe Message-ID: Date: Thu, 9 Jul 2020 07:53:07 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20200709133249.GC12769@casper.infradead.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: io-uring-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 7/9/20 7:32 AM, Matthew Wilcox wrote: > On Thu, Jul 09, 2020 at 02:26:11PM +0100, Christoph Hellwig wrote: >> On Thu, Jul 09, 2020 at 12:10:36PM +0100, Matthew Wilcox wrote: >>> On Thu, Jul 09, 2020 at 11:17:05AM +0100, Christoph Hellwig wrote: >>>> I really don't like this series at all. If saves a single pointer >>>> but introduces a complicated machinery that just doesn't follow any >>>> natural flow. And there doesn't seem to be any good reason for it to >>>> start with. >>> >>> Jens doesn't want the kiocb to grow beyond a single cacheline, and we >>> want the ability to set the loff_t in userspace for an appending write, >>> so the plan was to replace the ki_complete member in kiocb with an >>> loff_t __user *ki_posp. >>> >>> I don't think it's worth worrying about growing kiocb, personally, >>> but this seemed like the easiest way to make room for a new pointer. >> >> The user offset pointer has absolutely no business in the the kiocb >> itself - it is a io_uring concept which needs to go into the io_kiocb, >> which has 14 bytes left in the last cache line in my build. It would >> fit in very well there right next to the result and user pointer. > > I agree. Jens doesn't. Stop putting words in my mouth, especially when they are totally untrue. I was opposed to growing struct io_rw in io_uring, which is where the extra append variable belonds, beyond a cacheline. You mentioned you could probably shave some bits out of struct kiocb, which is how this completion handling business came about. If kiocb was shrunk, then io_rw has room for the needed variable. At no point have I said that whatever we need to shove in there for io_uring should be in the kiocb, that would not make any sense. I'm just opposed to growing the per-op data field in io_kiocb beyond a cacheline. And that's especially true for something like append writes, which I don't consider super interesting. -- Jens Axboe