From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754073AbeC2SPu (ORCPT ); Thu, 29 Mar 2018 14:15:50 -0400 Received: from verein.lst.de ([213.95.11.211]:51632 "EHLO newverein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752555AbeC2SPq (ORCPT ); Thu, 29 Mar 2018 14:15:46 -0400 Date: Thu, 29 Mar 2018 20:15:45 +0200 From: Christoph Hellwig To: Logan Gunthorpe Cc: James Smart , linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, Christoph Hellwig , Sagi Grimberg Subject: Re: [PATCH 4/4] nvmet-fc: Use new SGL alloc/free helper for requests Message-ID: <20180329181545.GA16116@lst.de> References: <20180329160721.4691-1-logang@deltatee.com> <20180329160721.4691-5-logang@deltatee.com> <15f4d135-7600-02b3-f50f-ed8deddd7b98@broadcom.com> 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) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 29, 2018 at 11:02:10AM -0600, Logan Gunthorpe wrote: > Per the bug in the previous patch, I don't think that was ever a valid > assumption. It doesn't have anything to do with the sgl_alloc change > either. The dma_map interface is allowed to merge SGLs and that's why it > can return fewer nents than it was passed. I'm not sure how many or > which DMA ops actually do this which is why it hasn't actually > manifested itself as a bug; but it is part of how the interface is > specified to work. Most iommus can, it just is very unlikely do happen in block drivers given that the block layer already merges segments higher up.