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=-0.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 1FC83C433E1 for ; Thu, 9 Jul 2020 19:06:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E9F942078B for ; Thu, 9 Jul 2020 19:06:21 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="h0ry14in" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726509AbgGITGN (ORCPT ); Thu, 9 Jul 2020 15:06:13 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33360 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726482AbgGITGM (ORCPT ); Thu, 9 Jul 2020 15:06:12 -0400 Received: from mail-wr1-x441.google.com (mail-wr1-x441.google.com [IPv6:2a00:1450:4864:20::441]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 51ADBC08C5CE; Thu, 9 Jul 2020 12:06:12 -0700 (PDT) Received: by mail-wr1-x441.google.com with SMTP id r12so3474489wrj.13; Thu, 09 Jul 2020 12:06:12 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=Z1gOyGKslSEgJ3uSJ29Ov3ex1KeLqnCoWQCiP6rXu5g=; b=h0ry14inpKQY/lgHJlfsRpCXkn6trDC9VWetEduPFj/XVI13O84Lfqc/nMYTQhh47Z 3qddP59YfKyrznOyEQx2jyvWA81O8XFr7p7RoSxCbQ1GJxJ710rQSwpuabzwbnjquJvu vKTbqlCK41l/iCLzCusA1J3Dpu1Xxss1V5kTkq75L5cFmWojyG02o4VYvJnH5/GnVKJ+ kNEUbLENHG1VLeAk6AFSlouAYUK2bLpIKhRDfkvCg4Kn0+tVhF5iDCVyh5kQuaQD8sav 8VlIYTA0lpCIqBrcI+7aeW3zEPxT64K3a0M0gotyHnfWRAI6mNuy07OiLqyj7CWLJ6Ww G9AQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=Z1gOyGKslSEgJ3uSJ29Ov3ex1KeLqnCoWQCiP6rXu5g=; b=F/4Se9PUSbck1uygYBG+tGjVABHpyNOh0/tfWRSDbAQtEa96LMjdkUVMBLz1hpVQbT zk+R9kYsUgMZRroRDPRdUrXmBoeGLFtPPamS1K4ruUnJeuOwh0VPoOdlbGgt37oUn0IK D3+ooi1QGkhix/1K+ob14XSw+a/sI2J/wcQEdGLeTRTnPcYuyCpJzOZX/9+5uLZnSnc5 O+IngaW35790MoK8PWCP3fJ7xkujp4v0YvxUou71O5Ssw8Ey2AB3WPj7JXk3gEn4MfVh UbNO38X57CoSDrCYih8Jlr/KdNEwg6rAAm6xOPhoeJftc4kftuZF6VI+Hh480/7Zwp3E djEg== X-Gm-Message-State: AOAM532fPhcWdkDZ6WgJvYGU+qszLCF72Qlds09Bs5sHM/uEAgcyy3NA WPWGcyRxvPs4BaxwH276i1nsSg+sZYtnrPfpnek= X-Google-Smtp-Source: ABdhPJwLNiWelIIW1U0lqwsr/Exp78LayRoHPkAYDJ3WdTDokbN20vizSsKcVJ7zA1RQDN2wjNC90ggUTGSyekhCbxA= X-Received: by 2002:adf:8444:: with SMTP id 62mr61802850wrf.278.1594321570845; Thu, 09 Jul 2020 12:06:10 -0700 (PDT) MIME-Version: 1.0 References: <1593974870-18919-1-git-send-email-joshi.k@samsung.com> <1593974870-18919-5-git-send-email-joshi.k@samsung.com> <20200709085501.GA64935@infradead.org> <20200709140053.GA7528@infradead.org> <2270907f-670c-5182-f4ec-9756dc645376@kernel.dk> In-Reply-To: From: Kanchan Joshi Date: Fri, 10 Jul 2020 00:35:43 +0530 Message-ID: Subject: Re: [PATCH v3 4/4] io_uring: add support for zone-append To: Jens Axboe Cc: Christoph Hellwig , Kanchan Joshi , viro@zeniv.linux.org.uk, bcrl@kvack.org, Damien.LeMoal@wdc.com, asml.silence@gmail.com, linux-fsdevel@vger.kernel.org, =?UTF-8?Q?Matias_Bj=C3=B8rling?= , linux-kernel@vger.kernel.org, linux-aio@kvack.org, io-uring@vger.kernel.org, linux-block@vger.kernel.org, Selvakumar S , Nitesh Shetty , Javier Gonzalez Content-Type: text/plain; charset="UTF-8" Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Fri, Jul 10, 2020 at 12:20 AM Jens Axboe wrote: > > On 7/9/20 12:36 PM, Kanchan Joshi wrote: > > On Thu, Jul 9, 2020 at 7:36 PM Jens Axboe wrote: > >> > >> On 7/9/20 8:00 AM, Christoph Hellwig wrote: > >>> On Thu, Jul 09, 2020 at 07:58:04AM -0600, Jens Axboe wrote: > >>>>> We don't actually need any new field at all. By the time the write > >>>>> returned ki_pos contains the offset after the write, and the res > >>>>> argument to ->ki_complete contains the amount of bytes written, which > >>>>> allow us to trivially derive the starting position. > > > > Deriving starting position was not the purpose at all. > > But yes, append-offset is not needed, for a different reason. > > It was kept for uring specific handling. Completion-result from lower > > layer was always coming to uring in ret2 via ki_complete(....,ret2). > > And ret2 goes to CQE (and user-space) without any conversion in between. > > For polled-completion, there is a short window when we get ret2 but cannot > > write into CQE immediately, so thought of storing that in append_offset > > (but should not have done, solving was possible without it). > > > > FWIW, if we move to indirect-offset approach, append_offset gets > > eliminated automatically, because there is no need to write to CQE > > itself. > > > >>>> Then let's just do that instead of jumping through hoops either > >>>> justifying growing io_rw/io_kiocb or turning kiocb into a global > >>>> completion thing. > >>> > >>> Unfortunately that is a totally separate issue - the in-kernel offset > >>> can be trivially calculated. But we still need to figure out a way to > >>> pass it on to userspace. The current patchset does that by abusing > >>> the flags, which doesn't really work as the flags are way too small. > >>> So we somewhere need to have an address to do the put_user to. > >> > >> Right, we're just trading the 'append_offset' for a 'copy_offset_here' > >> pointer, which are stored in the same spot... > > > > The address needs to be stored somewhere. And there does not seem > > other option but to use io_kiocb? > > That is where it belongs, not sure this was ever questioned. And inside > io_rw at that. > > > The bigger problem with address/indirect-offset is to be able to write > > to it during completion as process-context is different. Will that > > require entering into task_work_add() world, and may make it costly > > affair? > > It might, if you have IRQ context for the completion. task_work isn't > expensive, however. It's not like a thread offload. > > > Using flags have not been liked here, but given the upheaval involved so > > far I have begun to feel - it was keeping things simple. Should it be > > reconsidered? > > It's definitely worth considering, especially since we can use cflags > like Pavel suggested upfront and not need any extra storage. But it > brings us back to the 32-bit vs 64-bit discussion, and then using blocks > instead of bytes. Which isn't exactly super pretty. > I agree that what we had was not great. Append required special treatment (conversion for sector to bytes) for io_uring. And we were planning a user-space wrapper to abstract that. But good part (as it seems now) was: append result went along with cflags at virtually no additional cost. And uring code changes became super clean/minimal with further revisions. While indirect-offset requires doing allocation/mgmt in application, io-uring submission and in completion path (which seems trickier), and those CQE flags still get written user-space and serve no purpose for append-write. -- Joshi