From mboxrd@z Thu Jan 1 00:00:00 1970 From: John Hubbard Subject: Re: [PATCH v2] mmap.2: MAP_FIXED updated documentation Date: Wed, 6 Dec 2017 13:21:25 -0800 Message-ID: References: <20171204021411.4786-1-jhubbard@nvidia.com> <20171204105549.GA31332@rei> <20171205070510.aojohhvixijk3i27@dhcp22.suse.cz> <2cff594a-b481-269d-dd91-ff2cc2f4100a@nvidia.com> <20171206100118.GA13979@rei> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20171206100118.GA13979@rei> Content-Language: en-US Sender: linux-arch-owner@vger.kernel.org To: Cyril Hrubis Cc: Michal Hocko , Michael Kerrisk , linux-man , linux-api@vger.kernel.org, Michael Ellerman , linux-mm@kvack.org, LKML , linux-arch@vger.kernel.org, Jann Horn , Matthew Wilcox List-Id: linux-man@vger.kernel.org On 12/06/2017 02:01 AM, Cyril Hrubis wrote: > Hi! >> (It does seem unfortunate that the man page cannot help the programmer >> actually write correct code here. He or she is forced to read the kernel >> implementation, in order to figure out the true alignment rules. I was >> hoping we could avoid that.) > > It would be nice if we had this information exported somehere so that we > do not have to rely on per-architecture ifdefs. > > What about adding MapAligment or something similar to the /proc/meminfo? > What's the use case you envision for that? I don't see how that would be better than using SHMLBA, which is available at compiler time. Because unless someone expects to be able to run an app that was compiled for Arch X, on Arch Y (surely that's not requirement here?), I don't see how the run-time check is any better. Or maybe you're thinking that since the SHMLBA cannot be put in the man pages, we could instead provide MapAlignment as sort of a different way to document the requirement?