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=-5.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 27DCFC433DF for ; Fri, 16 Oct 2020 13:58:20 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (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 3AB7920848 for ; Fri, 16 Oct 2020 13:58:19 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="M/NELD9T" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3AB7920848 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=fuI9XDFPg0Zt9e8nbd+XU4F+D8WtDOJ9d9X7QK5fFZE=; b=M/NELD9TfGWyB+oq5Y7HnL9X8 iiOfbFRo09B97VTEqc+7SB/z4WvOdlBGj4OtX3K0ehZW0QDOJo2IY0v8Rrp9eLWShPYLsGehYlwHV 92IYhgm6aMbGKPt6RZJEC5EwWEdkWGaAy57rCo25w0uLQ2qmcTDwveqx2UjXYasxHZ8vx5jHgLh1z QIhGnbxnhMBeF2cddQ4FiT6mBe/o7p74BNkEXt/liAbrZvUpnBvUgc79chUWnbKev63gkIxzte/oT pf2lMj8blIMKrYLt8n2J029BNUZj6FE8Yu5ruwUm6UYj/IF6nsIOx65kqoLr4OfTmRSWYykZrK65f 9I4aRmlyA==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kTQFH-0003rq-9R; Fri, 16 Oct 2020 13:58:11 +0000 Received: from verein.lst.de ([213.95.11.211]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1kTQFB-0003qN-RA for linux-nvme@lists.infradead.org; Fri, 16 Oct 2020 13:58:06 +0000 Received: by verein.lst.de (Postfix, from userid 2407) id 153B767357; Fri, 16 Oct 2020 15:58:00 +0200 (CEST) Date: Fri, 16 Oct 2020 15:57:59 +0200 From: Christoph Hellwig To: Logan Gunthorpe Subject: Re: [PATCH] nvmet-passthru: Cleanup nvmet_passthru_map_sg() Message-ID: <20201016135759.GA4685@lst.de> References: <20201009231816.1524-1-logang@deltatee.com> <20201015075640.GJ14082@lst.de> <20201015180148.GA23377@lst.de> MIME-Version: 1.0 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-20201016_095805_999311_5D6AED96 X-CRM114-Status: GOOD ( 14.86 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Sagi Grimberg , Chaitanya Kulkarni , Christoph Hellwig , linux-nvme@lists.infradead.org, Douglas Gilbert 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, Oct 15, 2020 at 12:40:52PM -0600, Logan Gunthorpe wrote: > > But those are entirely unrelated to the bio size. BIO_MAX_PAGES is > > 256, so with 4k pages and assuming none can't be merged that is 1MB, > > while max_segments/max_hw_sectors could be something much larger. > > Isn't it constrained by max_segments which is set to NVME_MAX_SEGS=127 > (for PCI)... less than BIO_MAX_PAGES... nvmet-passthrough is not limited to work on PCIe controllers. And even if it did relying on an implicit limit like that is a time bomb. I have work pending for one of the next merge windows to lift that limit for example, and I would not have thought that nvmet-passthrough relies on it in any way. > Would the NVME driver even work if max_segments was greater than > BIO_MAX_PAGES? Correct me if I'm wrong, but it looks like > blk_rq_map_sg() will only map one bio within a request. So there has to > be one bio per request by the time it hits nvme_map_data()... blk_rq_map_sg maps the bio chain. Take a look at the for_each_bio loop in __blk_bios_map_sg. > If you want me to send a patch to future proof the MDTS limit with > BIO_MAX_PAGES, I can do that, but it doesn't look like it will have any > effect right now unless big things change. Yes, please do. _______________________________________________ Linux-nvme mailing list Linux-nvme@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-nvme