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 9A730C27C5E for ; Tue, 11 Jun 2024 05:47:40 +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=d/Xvwk8apUZsol+MDSIOy35JXYnSVjueR83rSqb25FM=; b=MlGS3namja1ubk9S4gm5CzRInN 0C07s9kSkdnRjbAFUpsceaMl4NpJxMEzlYcu7r/3sUoQz+TpSLo4c2+pGJgPHY3/fEZfS5naNPBod IHZRLg91+VuAcGFg+doKgpmVwS8wS3XZeFiGQuul07sA3/Y+g3Zgubq+guHVdPPxIY9ZvRcq154/g VRB8314hDAHakYUbvQY+HCX08Wz3C9+UayGwsdcm/6MWnhnAyWPAEVF+qKGbMe6l6phHOQbkQ5xpc Tm6yb8TCmUrC3n5dKuOboUAB3UqHh4xQS4HaEuG6e7yQkQA5I4JfwEo/NAIIG7sNY0bUa+H7Sem5q r0LIVQ8w==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1sGuM5-00000007ZbM-3tP1; Tue, 11 Jun 2024 05:47:37 +0000 Received: from verein.lst.de ([213.95.11.211]) by bombadil.infradead.org with esmtps (Exim 4.97.1 #2 (Red Hat Linux)) id 1sGuM2-00000007ZZn-36fj for linux-nvme@lists.infradead.org; Tue, 11 Jun 2024 05:47:36 +0000 Received: by verein.lst.de (Postfix, from userid 2407) id BD8C367373; Tue, 11 Jun 2024 07:47:26 +0200 (CEST) Date: Tue, 11 Jun 2024 07:47:26 +0200 From: Christoph Hellwig To: Keith Busch Cc: Christoph Hellwig , "Martin K. Petersen" , Kanchan Joshi , axboe@kernel.dk, sagi@grimberg.me, linux-nvme@lists.infradead.org, javier.gonz@samsung.com, bvanassche@acm.org, gost.dev@samsung.com, Hui Qi , Nitesh Shetty Subject: Re: [PATCH v2] nvme: enable FDP support Message-ID: <20240611054726.GA2680@lst.de> References: <20240528150233.55562-1-joshi.k@samsung.com> <20240608051740.GA24010@lst.de> <5e686875-21de-869d-4b19-bdd9e272d690@samsung.com> <20240610115541.GB19495@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-20240610_224734_954724_EEE64A42 X-CRM114-Status: GOOD ( 15.85 ) 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 Mon, Jun 10, 2024 at 08:52:12AM -0600, Keith Busch wrote: > I agree the FDP setup is complicated, but none of that is taken on by > the driver. It just discovers the capabilities and maps an arbitrary > software "hint" to an arbitrary device "hint". It's up to the > application to use those optimally; the driver just performs the > requested mapping. > > Is it because the names of those hints indicate data lifetime? These are > just arbitrary numbers used by applications to separate placement. If > they were called HINT_A, HINT_B, HINT_C, would that make this ok? No, the other problem is that FDP very much has an implicit contract that the host actually aligns to it resources units, and actually has a really complicated mangement. It's not a simple throw a lifetime hint at the drive. Note that the implicit is indeed very implicit - it is a really horrible spec with a lot of assumptions but nothing actually enforcing it. If you just use it for dumb lifetime hints changes are that you actually increase write amplificiation.