From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bart Van Assche Subject: Re: [PATCH 11/11] IB/srp: Prevent mapping failures Date: Mon, 25 Apr 2016 09:16:18 -0700 Message-ID: <571E42D2.70705@sandisk.com> References: <571A936F.7040409@sandisk.com> <571A94AF.7000609@sandisk.com> <20160424083538.GF7974@leon.nu> <571D6975.2020905@sandisk.com> <20160425055433.GG7974@leon.nu> <571DE793.6090705@grimberg.me> <20160425155320.GH7974@leon.nu> Mime-Version: 1.0 Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20160425155320.GH7974-2ukJVAZIZ/Y@public.gmane.org> Sender: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: leon-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, Sagi Grimberg Cc: Doug Ledford , Christoph Hellwig , Laurence Oberman , "linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" List-Id: linux-rdma@vger.kernel.org On 04/25/2016 08:53 AM, Leon Romanovsky wrote: > On Mon, Apr 25, 2016 at 12:46:59PM +0300, Sagi Grimberg wrote: >> >>>>>> + max_max_sectors = (srp_dev->max_pages_per_mr - 1) << >>>>>> + (ilog2(srp_dev->mr_page_size) - 9); >>>>> >>>>> From my understanding, srp_dev->max_pages_per_mr can be equal to 1, in >>>>> case device will advertise it. >>>>> >>>>> Is this understanding correct? >>>>> Will the code work in such case? >>>> >>>> Hello Leon, >>>> >>>> I'm not sure a HCA driver exists for which max_pages_per_mr == 1. >>>> Additionally, I'm not sure such a driver would be useful because such a >>>> driver would limit the maximum data transfer size for the iSER protocol to 4 >>>> KB. That is too low to reach good performance. >>> >>> Bart and Laurence, >>> You are raising valuable arguments about sanity of setting srp_dev->max_pages_per_mr >>> to be equal 1. I totally agree with you that it is insane, however my >>> original question was "does the code support such value?" >> >> I don't see why we should worry about imaginary devices. > > It is called corner case and the code supports it. I can add a WARN_ON_ONCE() statement for max_pages_per_mr == 1. That will make it easy to figure out where to start looking if in the future a HCA driver would be added that causes max_pages_per_mr == 1. Bart. -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html