linux-kernel - Re: [RFC 0/8] Define coherent device memory node

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Date:   Wed, 26 Oct 2016 12:07:21 -0400
From:   Jerome Glisse <j.glisse@...il.com>
To:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:     Anshuman Khandual <khandual@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org, mhocko@...e.com,
        js1304@...il.com, vbabka@...e.cz, mgorman@...e.de,
        minchan@...nel.org, akpm@...ux-foundation.org,
        bsingharora@...il.com
Subject: Re: [RFC 0/8] Define coherent device memory node

On Wed, Oct 26, 2016 at 04:39:19PM +0530, Aneesh Kumar K.V wrote:
> Jerome Glisse <j.glisse@...il.com> writes:
> 
> > On Tue, Oct 25, 2016 at 09:56:35AM +0530, Aneesh Kumar K.V wrote:
> >> Jerome Glisse <j.glisse@...il.com> writes:
> >> 
> >> > On Mon, Oct 24, 2016 at 10:01:49AM +0530, Anshuman Khandual wrote:
> >> >
> >> I looked at the hmm-v13 w.r.t migration and I guess some form of device
> >> callback/acceleration during migration is something we should definitely
> >> have. I still haven't figured out how non addressable and coherent device
> >> memory can fit together there. I was waiting for the page cache
> >> migration support to be pushed to the repository before I start looking
> >> at this closely.
> >> 
> >
> > The page cache migration does not touch the migrate code path. My issue with
> > page cache is writeback. The only difference with existing migrate code is
> > refcount check for ZONE_DEVICE page. Everything else is the same.
> 
> What about the radix tree ? does file system migrate_page callback handle
> replacing normal page with ZONE_DEVICE page/exceptional entries ?
> 

It use the exact same existing code (from mm/migrate.c) so yes the radix tree
is updated and buffer_head are migrated.

Jérôme