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 D6137C432BE 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 C05156103B for ; Fri, 20 Aug 2021 11:11:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237660AbhHTLMV (ORCPT ); Fri, 20 Aug 2021 07:12:21 -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-block@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 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=-0.7 required=3.0 tests=BAYES_00,DKIM_ADSP_CUSTOM_MED, DKIM_SIGNED,DKIM_VALID,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 6B519C4338F for ; Fri, 20 Aug 2021 11:12:09 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 316A56103B for ; Fri, 20 Aug 2021 11:12:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 316A56103B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:Cc:To:Subject:Message-ID:Date:From: In-Reply-To:References:MIME-Version:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=2W6FIH6kb/4V8+FGgpqK85bnj2AlPpddN+p/VFBT0ms=; b=AE6S78hG7Nicpt AjUV2yYb16rFo1HfG/GE7ihuTgK/q4pxhoXCgpf9exLe+504XjnwsD2P9rAe3IRAPEvet12878gr1 52uiU+LEXgnEbVK43vIzju8zFFqI3EpL+dxRQc/q/Y0mv9FjJB2n5rNHYADf+Qa5aFBFp9vLlAba+ VHu9AdyJVvWZ6tryRg5MWUjpj0AB+R1HzdPnx52V3z6zfk6Z5wi3wZTKj+lC2faEhSsFo49AadwDK MyWyrIFR4ng5jrn7Xv+sykuUqnwqfjK+eVuBy43asIx9ZuB5jSrwl/YyZu66WBgDfwC71J0F759NB 3KD8io3P51MkEZarj+cw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mH2R7-00AlU8-Vq; Fri, 20 Aug 2021 11:11:46 +0000 Received: from mail-wr1-x431.google.com ([2a00:1450:4864:20::431]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1mH2R5-00AlSz-9i for linux-nvme@lists.infradead.org; Fri, 20 Aug 2021 11:11:44 +0000 Received: by mail-wr1-x431.google.com with SMTP id n5so1343322wro.12 for ; 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=hQ/wmMyl+GqxjitB+eUkqpZ4d9s/vtKdcbstfEZc/m2F8KjPIrNmKJAXZ8YIqjXxZH 1aRMp+OEEmMDR7yWyBKTw7ejwrVYhgVehsIEcOrVHhv/qMjpf1JLSyIf1QEKnD36jCsy OIX2PEm62lXr5TNcFQ5DddA7CFuh+UZMVDKe7X5bypjNs/qmNeWyJt3RMfJLKGYXZmZ9 QP/as46wz/krN+4UECRT7rE6w9qMXwi+TLmltpBxQvT726xwdaWGHc1wG6I1Wv1SBN71 0Sj1xdNCvNIsSLhByOKEGSj8wY4MWVwHyPbCr5ft/qFvndpG0NPPTmkxpWPIFgj3iLqz JLHA== X-Gm-Message-State: AOAM530uGeGFxC5+xj0soBeVgbCFRA5E+pd1AB3gPd4U4LdMHnSmcZEr Y4dzcWlMyh0X42TqLZqlBsn6VVV6N1ZqO0+aSYg= 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 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210820_041143_370157_2B8284E4 X-CRM114-Status: GOOD ( 20.75 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.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 _______________________________________________ Linux-nvme mailing list Linux-nvme@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-nvme 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=-0.7 required=3.0 tests=BAYES_00,DKIM_ADSP_CUSTOM_MED, 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 8DD37C4338F for ; Mon, 23 Aug 2021 06:40:36 +0000 (UTC) Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 2F0156127B for ; Mon, 23 Aug 2021 06:40:36 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 2F0156127B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=tempfail smtp.mailfrom=redhat.com Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-38-kC17T5fKN7yjNoEi0idARg-1; Mon, 23 Aug 2021 02:40:33 -0400 X-MC-Unique: kC17T5fKN7yjNoEi0idARg-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 17E3D1082933; Mon, 23 Aug 2021 06:40:24 +0000 (UTC) Received: from colo-mx.corp.redhat.com (colo-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.21]) by smtp.corp.redhat.com (Postfix) with ESMTPS id EA74F6A905; Mon, 23 Aug 2021 06:40:23 +0000 (UTC) Received: from lists01.pubmisc.prod.ext.phx2.redhat.com (lists01.pubmisc.prod.ext.phx2.redhat.com [10.5.19.33]) by colo-mx.corp.redhat.com (Postfix) with ESMTP id BC28E4A700; Mon, 23 Aug 2021 06:40:23 +0000 (UTC) Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) by lists01.pubmisc.prod.ext.phx2.redhat.com (8.13.8/8.13.8) with ESMTP id 17KBBoN6002988 for ; Fri, 20 Aug 2021 07:11:50 -0400 Received: by smtp.corp.redhat.com (Postfix) id 382F120B6640; Fri, 20 Aug 2021 11:11:50 +0000 (UTC) Received: from mimecast-mx02.redhat.com (mimecast02.extmail.prod.ext.rdu2.redhat.com [10.11.55.18]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 33C4A20B6637 for ; Fri, 20 Aug 2021 11:11:46 +0000 (UTC) Received: from us-smtp-1.mimecast.com (us-smtp-1.mimecast.com [207.211.31.81]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id AC0D58011AF for ; Fri, 20 Aug 2021 11:11:46 +0000 (UTC) Received: from mail-wr1-f47.google.com (mail-wr1-f47.google.com [209.85.221.47]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-589-UNcef0NdNC2JZaTojpXMYQ-1; Fri, 20 Aug 2021 07:11:42 -0400 X-MC-Unique: UNcef0NdNC2JZaTojpXMYQ-1 Received: by mail-wr1-f47.google.com with SMTP id q11so13703426wrr.9; Fri, 20 Aug 2021 04:11:42 -0700 (PDT) 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=ce6c4qd/KSu2gOp2pP4LCa38DdxT4jZrQa7NnNPjDvYYA2oOQX4JfcwyxwkhWCvn8U LE9v0WqZ/7yqxj1zGDyj8Mgr71ssCKfoCAM5zcOrSezPgmBekkEZpnhi3rcLnfI+Xc0z 9RsvyG2zjsexxgmutIDH7X7k7ep/moEHb+wZqvlq7Lw5zZrgznzWs94DnDAIvAg0m5YE YbXL4g3ReF+7AUdmmARKoRMVGzBdGFNvYBYZsIC9bOGqmFQmGI0EI2pAJ63XFgwrhi+F EXRauPCNAjzCotv8YsoCYtfAYD+pBNybPjwtr0MxdBLSOFi5cPip+AxHUTYe8iivXqGX V5Vg== X-Gm-Message-State: AOAM533FHaoDANtMst9lB3o+hXF1Jck7VYFbzn+jT/2NM4rfqFFAMyj8 bJXBeOsw/gTKKXQ/+tUc9HK93g3CJz0xjh3DjDc= 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: To: "Martin K. Petersen" X-Mimecast-Impersonation-Protect: Policy=CLT - Impersonation Protection Definition; Similar Internal Domain=false; Similar Monitored External Domain=false; Custom External Domain=false; Mimecast External Domain=false; Newly Observed Domain=false; Internal User Name=false; Custom Display Name List=false; Reply-to Address Mismatch=false; Targeted Threat Dictionary=false; Mimecast Threat Dictionary=false; Custom Threat Dictionary=false X-Scanned-By: MIMEDefang 2.78 on 10.11.54.4 X-loop: dm-devel@redhat.com X-Mailman-Approved-At: Mon, 23 Aug 2021 02:39:55 -0400 Cc: snitzer@redhat.com, djwong@kernel.org, linux-nvme@lists.infradead.org, dm-devel@redhat.com, Christoph Hellwig , agk@redhat.com, bvanassche@acm.org, linux-scsi@vger.kernel.org, nitheshshetty@gmail.com, Matthew Wilcox , Nitesh Shetty , kch@kernel.org, SelvaKumar S , Selva Jove , linux-block@vger.kernel.org, mpatocka@redhat.com, Keith Busch , Jens Axboe , Damien Le Moal , KANCHAN JOSHI , linux-api@vger.kernel.org, Johannes Thumshirn , linux-fsdevel@vger.kernel.org, Javier Gonzalez , Pavel Begunkov Subject: Re: [dm-devel] [PATCH 3/7] block: copy offload support infrastructure X-BeenThere: dm-devel@redhat.com X-Mailman-Version: 2.1.12 Precedence: junk List-Id: device-mapper development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dm-devel-bounces@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit 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 -- dm-devel mailing list dm-devel@redhat.com https://listman.redhat.com/mailman/listinfo/dm-devel