linux-kernel - Re: [RFC] mmap(MAP

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Message-ID: <c00b355a-cfb7-a4e0-56a3-01430dc9e9f5@oracle.com>
Date:   Wed, 4 Oct 2017 10:08:50 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Michal Nazarewicz <mina86@...a86.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-api@...r.kernel.org
Cc:     Marek Szyprowski <m.szyprowski@...sung.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Guy Shattah <sguy@...lanox.com>,
        Christoph Lameter <cl@...ux.com>
Subject: Re: [RFC] mmap(MAP_CONTIG)

On 10/04/2017 04:54 AM, Michal Nazarewicz wrote:
> On Tue, Oct 03 2017, Mike Kravetz wrote:
>> At Plumbers this year, Guy Shattah and Christoph Lameter gave a presentation
>> titled 'User space contiguous memory allocation for DMA' [1].  The slides
>> point out the performance benefits of devices that can take advantage of
>> larger physically contiguous areas.
> 
> Issue I have is that kind of memory needed may depend on a device.  Some
> may require contiguous blocks.  Some may support scatter-gather.  Some
> may be behind IO-MMU and not care either way.
> 
> Furthermore, I feel déjà vu.  Wasn’t dmabuf supposed to address this
> issue?

Thanks Michal,

I was unaware of dmabuf and am just now looking at capabilities.  The
question is whether or not the IB driver writers requesting mmap(MAP_CONTIG)
functionality could make use of dmabuf.  That is out of my are of expertise,
so I will let them reply.

-- 
Mike Kravetz