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Message-ID: <5f4fc834-274a-b8f1-bda0-5bcddc5902ed@nvidia.com> Date: Tue, 5 Dec 2017 23:33:58 -0800 From: John Hubbard <jhubbard@...dia.com> To: Matthew Wilcox <willy@...radead.org>, Michael Ellerman <mpe@...erman.id.au> CC: Cyril Hrubis <chrubis@...e.cz>, Michal Hocko <mhocko@...nel.org>, Kees Cook <keescook@...omium.org>, Linux API <linux-api@...r.kernel.org>, Khalid Aziz <khalid.aziz@...cle.com>, Andrew Morton <akpm@...ux-foundation.org>, Russell King - ARM Linux <linux@...linux.org.uk>, Andrea Arcangeli <aarcange@...hat.com>, Linux-MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>, linux-arch <linux-arch@...r.kernel.org>, Florian Weimer <fweimer@...hat.com>, Abdul Haleem <abdhalee@...ux.vnet.ibm.com>, Joel Stanley <joel@....id.au> Subject: Re: [PATCH 0/2] mm: introduce MAP_FIXED_SAFE On 12/05/2017 11:03 PM, Matthew Wilcox wrote: > On Tue, Dec 05, 2017 at 08:54:35PM -0800, Matthew Wilcox wrote: >> On Wed, Dec 06, 2017 at 03:51:44PM +1100, Michael Ellerman wrote: >>> Cyril Hrubis <chrubis@...e.cz> writes: >>> >>>> Hi! >>>>>> MAP_FIXED_UNIQUE >>>>>> MAP_FIXED_ONCE >>>>>> MAP_FIXED_FRESH >>>>> >>>>> Well, I can open a poll for the best name, but none of those you are >>>>> proposing sound much better to me. Yeah, naming sucks... >>>> >>>> Given that MAP_FIXED replaces the previous mapping MAP_FIXED_NOREPLACE >>>> would probably be a best fit. >>> >>> Yeah that could work. >>> >>> I prefer "no clobber" as I just suggested, because the existing >>> MAP_FIXED doesn't politely "replace" a mapping, it destroys the current >>> one - which you or another thread may be using - and clobbers it with >>> the new one. >> >> It's longer than MAP_FIXED_WEAK :-P >> >> You'd have to be pretty darn strong to clobber an existing mapping. > > I think we're thinking about this all wrong. We shouldn't document it as > "This is a variant of MAP_FIXED". We should document it as "Here's an > alternative to MAP_FIXED". > > So, just like we currently say "exactly one of MAP_SHARED or MAP_PRIVATE", > we could add a new paragraph saying "at most one of MAP_FIXED or > MAP_REQUIRED" and "any of the following values". > > Now, we should implement MAP_REQUIRED as having each architecture > define _MAP_NOT_A_HINT, and then #define MAP_REQUIRED (MAP_FIXED | > _MAP_NOT_A_HINT), but that's not information to confuse users with. > > Also, that lets us add a third option at some point that is Yet Another > Way to interpret the 'addr' argument, by having MAP_FIXED clear and > _MAP_NOT_A_HINT set. > > I'm not set on MAP_REQUIRED. I came up with some awful names > (MAP_TODDLER, MAP_TANTRUM, MAP_ULTIMATUM, MAP_BOSS, MAP_PROGRAM_MANAGER, > etc). But I think we should drop FIXED from the middle of the name. > In that case, maybe: MAP_EXACT ? ...because that's the characteristic behavior. It doesn't clobber, but you don't need to say that in the name, now that we're not including _FIXED_ in the middle. thanks, John Hubbard NVIDIA
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