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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id CB862D0C601 for ; Fri, 25 Oct 2024 12:21:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=2gR5DYOQIaIYHxPAgnKsME6durGnBAfGyV2RML7XQHQ=; b=qn/EWlzItY5EqrRrbQc3Rz3f3q JNqs5c3sDSvjw4HY7mncq3Qv27VHvANZHWFGOOJyFEpxn8by64zOozMh7DwYXk3s+qfaBIujr8ri8 VdiswS2W/A3PBqZwkUG6pDkf9RADGtr+0XP7zBlE9XnqLYEG/VdFVfC+WUOq7caz0nZujJr/w8OeH vNfXY6eljqCYga7BaQLSoj2u5orrUTSKaA6gspvL5AsAFMC4jQExOKF9eLzK6kiOv6shBFw5/Povn O/6ww+GE2I/qN8Pf1oRKWHZSvRioOMVIwRwhI6T5mQUUa6p1t2mFMXNo743OEdK5rApKrXGROLKYL AbFNjrnw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1t4JJh-00000003dLz-12gU; Fri, 25 Oct 2024 12:21:21 +0000 Received: from verein.lst.de ([213.95.11.211]) by bombadil.infradead.org with esmtps (Exim 4.98 #2 (Red Hat Linux)) id 1t4JIZ-00000003d6X-1DZJ for linux-nvme@lists.infradead.org; Fri, 25 Oct 2024 12:20:12 +0000 Received: by verein.lst.de (Postfix, from userid 2407) id 75910227A88; Fri, 25 Oct 2024 14:20:04 +0200 (CEST) Date: Fri, 25 Oct 2024 14:20:04 +0200 From: Christoph Hellwig To: Keith Busch Cc: Christoph Hellwig , Keith Busch , linux-block@vger.kernel.org, linux-nvme@lists.infradead.org, axboe@kernel.dk, io-uring@vger.kernel.org, linux-fsdevel@vger.kernel.org, joshi.k@samsung.com, javier.gonz@samsung.com Subject: Re: [PATCHv8 2/6] block: use generic u16 for write hints Message-ID: <20241025122004.GA22710@lst.de> References: <20241017160937.2283225-1-kbusch@meta.com> <20241017160937.2283225-3-kbusch@meta.com> <20241018054643.GA20262@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20241025_052011_491572_C5C379EA X-CRM114-Status: GOOD ( 16.97 ) 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: , Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org On Thu, Oct 24, 2024 at 01:45:02PM -0600, Keith Busch wrote: > I'm not sure I follow this feedback. The SCSI feature is defined as a > lifetime stream association in SBC-5. So it's still a stream for SCSI, > but you want to call it "WRITE_HINT", which is not a term used in the > SCSI spec for this feature. But, you want to call it STREAM_SEPARATION > for NVMe only, even though the FDP spec doesn't use that term? What's > wrong with just calling it a generic hint support feature? The "Constrained Streams with Data Lifetimes" are called streams for political reasons but they are not. They are buckets of different data lifetimes. > I also don't see why SCSI couldn't use per-io hints just like this > enables for NVMe. The spec doesn't limit SCSI to just 5 streams, so this > provides a way to access them all through the raw block device. I don't mind passing per-I/O temperature hints to SCSI block devices. But we should not confuse a streams/FDP like streams that are different context which are assumed to be discarded together and have a concept of Stream Granularity Size or Reclaim Unit size with the data temperature hints that are at the storage level fundamentally per-I/O and just bucket into temperature group without any indication of data locality.