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From:   Jason Gunthorpe <jgg@mellanox.com>
To:     Logan Gunthorpe <logang@deltatee.com>
CC:     Jerome Glisse <jglisse@redhat.com>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
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        Felix Kuehling <Felix.Kuehling@amd.com>,
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        Joerg Roedel <jroedel@suse.de>,
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Subject: Re: [RFC PATCH 3/5] mm/vma: add support for peer to peer to device
 vma
Thread-Topic: [RFC PATCH 3/5] mm/vma: add support for peer to peer to device
 vma
Thread-Index: AQHUt/rA/dLikqWEmEaIytHIBNLPlqXGkyOAgAAJwICAAAX+AIAAEreAgAAFNYA=
Date:   Tue, 29 Jan 2019 20:58:35 +0000
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On Tue, Jan 29, 2019 at 01:39:49PM -0700, Logan Gunthorpe wrote:

> implement the mapping. And I don't think we should have 'special' vma's
> for this (though we may need something to ensure we don't get mapping
> requests mixed with different types of pages...).

I think Jerome explained the point here is to have a 'special vma'
rather than a 'special struct page' as, really, we don't need a
struct page at all to make this work.

If I recall your earlier attempts at adding struct page for BAR
memory, it ran aground on issues related to O_DIRECT/sgls, etc, etc.

This does seem to avoid that pitfall entirely as we can never
accidently get into the SGL system with this kind of memory or VMA?

Jason