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Date:   Sun, 15 Oct 2017 08:58:56 +0200
From:   Pavel Machek <pavel@....cz>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Christopher Lameter <cl@...ux.com>,
        Mike Kravetz <mike.kravetz@...cle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Michal Nazarewicz <mina86@...a86.com>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Guy Shattah <sguy@...lanox.com>,
        Anshuman Khandual <khandual@...ux.vnet.ibm.com>,
        Laura Abbott <labbott@...hat.com>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [RFC PATCH 3/3] mm/map_contig: Add mmap(MAP_CONTIG) support

Hi!

> Yes you wrote that already and my counter argument was that this generic
> posix interface shouldn't bypass virtual memory abstraction.
> 
> > > > The contiguous allocations are particularly useful for the RDMA API which
> > > > allows registering user space memory with devices.
> > >
> > > then make those devices expose an implementation of an mmap which does
> > > that. You would get both a proper access control (via fd), accounting
> > > and others.
> > 
> > There are numerous RDMA devices that would all need the mmap
> > implementation. And this covers only the needs of one subsystem. There are
> > other use cases.
> 
> That doesn't prevent providing a library function which could be reused
> by all those drivers. Nothing really too much different from
> remap_pfn_range.

So you'd suggest using ioctl() for allocating memory?

That sounds quite ugly to me... mmap(MAP_CONTIG) is not nice, either, but better than
each driver inventing custom interface...
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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