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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D0D49C4332F for ; Thu, 24 Nov 2022 00:05:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229732AbiKXAFS (ORCPT ); Wed, 23 Nov 2022 19:05:18 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34862 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229379AbiKXAFR (ORCPT ); Wed, 23 Nov 2022 19:05:17 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6F90A1095B1 for ; Wed, 23 Nov 2022 16:04:23 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1669248262; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=Swuw4Srtq7ILJ+Sr28sVCP8NRm0onxfQ8iNTcMfZrZ0=; b=XNHHclPtfi72KQDweZaRIGtA7374nibcudaelapbxDquOh71aJeCwrVD9BbYEida3WeW8U AsMhcySKe86vHtReRgNS2b2XcMOyfJ3Fq/DT8dwn1l7J+XIHIAnZXFsqx9vRYjCpLnSV0O TI7nui1rkiv4gpJs1qRhbfbFtgjosk4= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-655-eMnJ2nuQPZ63mU3GdK9XLA-1; Wed, 23 Nov 2022 19:04:21 -0500 X-MC-Unique: eMnJ2nuQPZ63mU3GdK9XLA-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 3935F29AB3E1; Thu, 24 Nov 2022 00:04:20 +0000 (UTC) Received: from T590 (ovpn-8-17.pek2.redhat.com [10.72.8.17]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 5DF81C15BB1; Thu, 24 Nov 2022 00:04:03 +0000 (UTC) Date: Thu, 24 Nov 2022 08:03:56 +0800 From: Ming Lei To: Nitesh Shetty Cc: axboe@kernel.dk, agk@redhat.com, snitzer@kernel.org, dm-devel@redhat.com, kbusch@kernel.org, hch@lst.de, sagi@grimberg.me, james.smart@broadcom.com, kch@nvidia.com, damien.lemoal@opensource.wdc.com, naohiro.aota@wdc.com, jth@kernel.org, viro@zeniv.linux.org.uk, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, linux-fsdevel@vger.kernel.org, anuj20.g@samsung.com, joshi.k@samsung.com, p.raghav@samsung.com, nitheshshetty@gmail.com, gost.dev@samsung.com, ming.lei@redhat.com Subject: Re: [PATCH v5 02/10] block: Add copy offload support infrastructure Message-ID: References: <20221123055827.26996-1-nj.shetty@samsung.com> <20221123055827.26996-3-nj.shetty@samsung.com> <20221123100712.GA26377@test-zns> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221123100712.GA26377@test-zns> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Wed, Nov 23, 2022 at 03:37:12PM +0530, Nitesh Shetty wrote: > On Wed, Nov 23, 2022 at 04:04:18PM +0800, Ming Lei wrote: > > On Wed, Nov 23, 2022 at 11:28:19AM +0530, Nitesh Shetty wrote: > > > Introduce blkdev_issue_copy which supports source and destination bdevs, > > > and an array of (source, destination and copy length) tuples. > > > Introduce REQ_COPY copy offload operation flag. Create a read-write > > > bio pair with a token as payload and submitted to the device in order. > > > Read request populates token with source specific information which > > > is then passed with write request. > > > This design is courtesy Mikulas Patocka's token based copy > > > > I thought this patchset is just for enabling copy command which is > > supported by hardware. But turns out it isn't, because blk_copy_offload() > > still submits read/write bios for doing the copy. > > > > I am just wondering why not let copy_file_range() cover this kind of copy, > > and the framework has been there. > > > > Main goal was to enable copy command, but community suggested to add > copy emulation as well. > > blk_copy_offload - actually issues copy command in driver layer. > The way read/write BIOs are percieved is different for copy offload. > In copy offload we check REQ_COPY flag in NVMe driver layer to issue > copy command. But we did missed it to add in other driver's, where they > might be treated as normal READ/WRITE. > > blk_copy_emulate - is used if we fail or if device doesn't support native > copy offload command. Here we do READ/WRITE. Using copy_file_range for > emulation might be possible, but we see 2 issues here. > 1. We explored possibility of pulling dm-kcopyd to block layer so that we > can readily use it. But we found it had many dependecies from dm-layer. > So later dropped that idea. Is it just because dm-kcopyd supports async copy? If yes, I believe we can reply on io_uring for implementing async copy_file_range, which will be generic interface for async copy, and could get better perf. > 2. copy_file_range, for block device atleast we saw few check's which fail > it for raw block device. At this point I dont know much about the history of > why such check is present. Got it, but IMO the check in generic_copy_file_checks() can be relaxed to cover blkdev cause splice does support blkdev. Then your bdev offload copy work can be simplified into: 1) implement .copy_file_range for def_blk_fops, suppose it is blkdev_copy_file_range() 2) inside blkdev_copy_file_range() - if the bdev supports offload copy, just submit one bio to the device, and this will be converted to one pt req to device - otherwise, fallback to generic_copy_file_range() > > > When I was researching pipe/splice code for supporting ublk zero copy[1], I > > have got idea for async copy_file_range(), such as: io uring based > > direct splice, user backed intermediate buffer, still zero copy, if these > > ideas are finally implemented, we could get super-fast generic offload copy, > > and bdev copy is really covered too. > > > > [1] https://lore.kernel.org/linux-block/20221103085004.1029763-1-ming.lei@redhat.com/ > > > > Seems interesting, We will take a look into this. BTW, that is probably one direction of ublk's async zero copy IO too. Thanks, Ming