linux-kernel - Re: [RFC PATCH 3/3] mm/map_contig: Add mmap(MAP

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Message-ID: <4994fc18-f0ee-300d-d61f-c1a1b63e55e4@redhat.com>
Date:   Mon, 16 Oct 2017 14:03:16 -0700
From:   Laura Abbott <labbott@...hat.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>,
        Michal Hocko <mhocko@...nel.org>
Cc:     Guy Shattah <sguy@...lanox.com>,
        Christopher Lameter <cl@...ux.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>,
        Anshuman Khandual <khandual@...ux.vnet.ibm.com>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [RFC PATCH 3/3] mm/map_contig: Add mmap(MAP_CONTIG) support

On 10/16/2017 01:32 PM, Mike Kravetz wrote:
> On 10/16/2017 11:07 AM, Michal Hocko wrote:
>> On Mon 16-10-17 10:43:38, Mike Kravetz wrote:
>>> Just to be clear, the posix standard talks about a typed memory object.
>>> The suggested implementation has one create a connection to the memory
>>> object to receive a fd, then use mmap as usual to get a mapping backed
>>> by contiguous pages/memory.  Of course, this type of implementation is
>>> not a requirement.
>>
>> I am not sure that POSIC standard for typed memory is easily
>> implementable in Linux. Does any OS actually implement this API?
> 
> A quick search only reveals Blackberry QNX and PlayBook OS.
> 
> Also somewhat related.  In a earlier thread someone pointed out this
> out of tree module used for contiguous allocations in SOC (and other?)
> environments.  It even has the option of making use of CMA.
> http://processors.wiki.ti.com/index.php/CMEM_Overview
> 

If we're at the point where we're discussing CMEM, I'd like to
point out that ion (drivers/staging/android/ion) already provides an
ioctl interface to allocate CMA and other types of memory. It's
mostly used for Android as the name implies. I don't pretend the
interface is perfect but it could be useful as a discussion point
for allocation interfaces.

Thanks,
Laura