From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lindbergh.monkeyblade.net (lindbergh.monkeyblade.net [23.128.96.19]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E10298460 for ; Mon, 16 Oct 2023 06:17:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=none Received: from verein.lst.de (verein.lst.de [213.95.11.211]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 71204DC; Sun, 15 Oct 2023 23:17:41 -0700 (PDT) Received: by verein.lst.de (Postfix, from userid 2407) id 834726732A; Mon, 16 Oct 2023 08:17:37 +0200 (CEST) Date: Mon, 16 Oct 2023 08:17:37 +0200 From: Christoph Hellwig To: Damien Le Moal Cc: Bart Van Assche , Jens Axboe , linux-block@vger.kernel.org, linux-scsi@vger.kernel.org, linux-fsdevel@vger.kernel.org, "Martin K . Petersen" , Christoph Hellwig , Niklas Cassel , Avri Altman , Bean Huo , Daejun Park , Hannes Reinecke Subject: Re: [PATCH v2 03/15] block: Support data lifetime in the I/O priority bitfield Message-ID: <20231016061737.GA26670@lst.de> References: <20231005194129.1882245-1-bvanassche@acm.org> <20231005194129.1882245-4-bvanassche@acm.org> <8aec03bb-4cef-9423-0ce4-c10d060afce4@kernel.org> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <8aec03bb-4cef-9423-0ce4-c10d060afce4@kernel.org> User-Agent: Mutt/1.5.17 (2007-11-01) X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_BLOCKED,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net On Fri, Oct 06, 2023 at 05:19:52PM +0900, Damien Le Moal wrote: > Your change seem to assume that it makes sense to be able to combine CDL with > lifetime hints. But does it really ? Yes, it does. > CDL is of dubious value for solid state > media and as far as I know, No, it's pretty useful and I'd bet my 2 cents that it will eventually show up in relevant standards and devices. Even if it wasn't making our user interfaces exclusive would be a massive pain. > The other question here if you really want to keep the bit separation approach > is: do we really need up to 64 different lifetime hints ? While the scsi > standard allows that much, does this many different lifetime make sense in > practice ? Can we ever think of a usecase that needs more than say 8 different > liftimes (3 bits) ? If you limit the number of possible lifetime hints to 8, > then we can keep 4 bits unused in the hint field for future features. Yes, I think this is the smoking gun. We should be fine with a much more limited number of lifetime hints, i.e. the user interface only exposes 5 hints, and supporting more in the in-kernel interfaces seems of rather doubtfuĊ€ use.