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

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Message-ID: <20171017105921.4w7rba2day3k4g4p@dhcp22.suse.cz>
Date:   Tue, 17 Oct 2017 12:59:21 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Guy Shattah <sguy@...lanox.com>
Cc:     Christopher Lameter <cl@...ux.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-api@...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>,
        Laura Abbott <labbott@...hat.com>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [RFC PATCH 3/3] mm/map_contig: Add mmap(MAP_CONTIG) support

On Tue 17-10-17 10:50:02, Guy Shattah wrote:
[...]
> > Well, we can provide a generic library functions for your driver to use so that
> > you do not have to care about implementation details but I do not think
> > exposing this API to the userspace in a generic fashion is a good idea.
> > Especially when the only usecase that has been thought through so far seems
> > to be a very special HW optimiztion.
> 
> Are you going to be OK with kernel API which implements contiguous
> memory allocation?

We already do have alloc_contig_range. It is a dumb allocator so it is
not very suitable for short term allocations.

> Possibly with mmap style?  Many drivers could utilize it instead of
> having their own weird and possibly non-standard way to allocate
> contiguous memory.  Such API won't be available for user space.

Yes, an mmap helper which performs and enforces some accounting would be a
good start.

> We can begin with implementing kernel API and postpone the userspace
> api discussion for a future date. if it is sufficient. We might not
> have to discuss it at all.

Yeah, that was my thinking as well.
-- 
Michal Hocko
SUSE Labs