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=-2.8 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,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 1C7D0C4338F for ; Fri, 20 Aug 2021 11:11:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EDF1F61057 for ; Fri, 20 Aug 2021 11:11:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236784AbhHTLMU (ORCPT ); Fri, 20 Aug 2021 07:12:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45490 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229847AbhHTLMU (ORCPT ); Fri, 20 Aug 2021 07:12:20 -0400 Received: from mail-wr1-x434.google.com (mail-wr1-x434.google.com [IPv6:2a00:1450:4864:20::434]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B3682C061575; Fri, 20 Aug 2021 04:11:42 -0700 (PDT) Received: by mail-wr1-x434.google.com with SMTP id v10so2467864wrd.4; Fri, 20 Aug 2021 04:11:42 -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=XTV41ORucx8ryF7oB1eYwysBWiCN8gKMFeTRn1Zj7AM=; b=MYvcDMXR87iOi7JK63t8cj54EEq9i8ZzrMq9tTqiUnWhDTDpZ+z4a4GCYAjq653LTa I0zDS4sQg1eW6rUqQCv1JNBNE6zrArt6rTFvGCFeg0Dbin816j8YZy9tgx6PsYbcoTGo pRvXznFW67AYmCqrOL/h4QHkXw0BeMbcThfam8AJkm+2c4RjnYPossT/rYuEPniF4uUP lgU4P6t/RauHcpJ985qi72+0T/B06GHTCsAkiEiv0WJP3v8HUf+Y+HDJVlu8p0kLKiGO 1NAaZJYEaqA0vmmOG6yNGc7LwnVlknJMuXwP7kGJLpVCuwHngy0M5vjxVKd3AAzIoPHD 6J+g== 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=XTV41ORucx8ryF7oB1eYwysBWiCN8gKMFeTRn1Zj7AM=; b=din9tUTwECWjTuz3y/YTtyHp2IxJbKlUz8bB6sS8JQQ1loaKMKTPghsBtE97uos58y yL1urZRYERvN4qKmkUhMDk2n7GgzFOhu7LIOuLplipLY40CJwhX2fKSZRK/4hS/Y+b6W 4GpsfFwU0AA4AtQLSXDJypXh92gsuWIGMbki2wZMdnZlNjML9XvIwrPeKBryVnfY8iZY 65Rhzc5dPVkZuAEnNnEjlx9mmV8TyjGbccyLwNWKvCCwYtPRyg31m21W/vPaUWk2I6V7 mAp6uJQCU+Y4xGCrlpGBGPcT0mgkV2aA+96Bp2rEs9qXXZkctz2uykBSxQutU3VFla/e keZA== X-Gm-Message-State: AOAM531+MiQjj00idO+VkZLpQm32GnH/T9ciNvbdF1jD/+kfZ0/8iPWH yTcMriFCGs5XYtaFESxy1YzzmCClX9cOgHDgWdo= X-Google-Smtp-Source: ABdhPJyHLBn4cAqZhoblha8bwzOCJdvxUWt4EpC0AJmYcZ2sxKZSuvBjXl3YiZg/qrMlyWLl4b6/2Ts3GXLe812W024= X-Received: by 2002:a5d:6991:: with SMTP id g17mr9619476wru.253.1629457901314; Fri, 20 Aug 2021 04:11:41 -0700 (PDT) MIME-Version: 1.0 References: <20210817101423.12367-1-selvakuma.s1@samsung.com> <20210817101423.12367-4-selvakuma.s1@samsung.com> In-Reply-To: From: Kanchan Joshi Date: Fri, 20 Aug 2021 16:41:15 +0530 Message-ID: Subject: Re: [PATCH 3/7] block: copy offload support infrastructure To: "Martin K. Petersen" Cc: SelvaKumar S , linux-nvme@lists.infradead.org, linux-block@vger.kernel.org, linux-api@vger.kernel.org, linux-scsi@vger.kernel.org, linux-fsdevel@vger.kernel.org, dm-devel@redhat.com, Keith Busch , Jens Axboe , Damien Le Moal , Pavel Begunkov , Johannes Thumshirn , Christoph Hellwig , Matthew Wilcox , kch@kernel.org, mpatocka@redhat.com, bvanassche@acm.org, djwong@kernel.org, snitzer@redhat.com, agk@redhat.com, Selva Jove , Nitesh Shetty , nitheshshetty@gmail.com, KANCHAN JOSHI , Javier Gonzalez Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On Thu, Aug 19, 2021 at 12:05 AM Martin K. Petersen wrote: > > > > Native copy offload is not supported for stacked devices. > > One of the main reasons that the historic attempts at supporting copy > offload did not get merged was that the ubiquitous deployment scenario, > stacked block devices, was not handled well. > > Pitfalls surrounding stacking has been brought up several times in > response to your series. It is critically important that both kernel > plumbing and user-facing interfaces are defined in a way that works for > the most common use cases. This includes copying between block devices > and handling block device stacking. Stacking being one of the most > fundamental operating principles of the Linux block layer! > > Proposing a brand new interface that out of the gate is incompatible > with both stacking and the copy offload capability widely implemented in > shipping hardware makes little sense. While NVMe currently only supports > copy operations inside a single namespace, it is surely only a matter of > time before that restriction is lifted. > > Changing existing interfaces is painful, especially when these are > exposed to userland. We obviously can't predict every field or feature > that may be needed in the future. But we should at the very least build > the infrastructure around what already exists. And that's where the > proposed design falls short... > Certainly, on user-space interface. We've got few cracks to be filled there, missing the future viability. But on stacking, can that be additive. Could you please take a look at the other response (comment from Bart) for the trade-offs. -- Joshi