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Date:   Sun, 15 Oct 2017 08:58:56 +0200
From:   Pavel Machek <>
To:     Michal Hocko <>
Cc:     Christopher Lameter <>,
        Mike Kravetz <>,,,,
        Marek Szyprowski <>,
        Michal Nazarewicz <>,
        "Aneesh Kumar K . V" <>,
        Joonsoo Kim <>,
        Guy Shattah <>,
        Anshuman Khandual <>,
        Laura Abbott <>,
        Vlastimil Babka <>
Subject: Re: [RFC PATCH 3/3] mm/map_contig: Add mmap(MAP_CONTIG) support


> 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...
(cesky, pictures)

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