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

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Message-Id: <87y41bcqow.fsf@linux.vnet.ibm.com>
Date:   Wed, 26 Oct 2016 16:39:19 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:     Jerome Glisse <j.glisse@...il.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

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 ?

>
> For writeback i need to use a bounce page so basicly i am trying to hook myself
> along the ISA bounce infrastructure for bio and i think it is the easiest path
> to solve this in my case.
>
> In your case where block device can also access the device memory you don't
> even need to use bounce page for writeback.
>

-aneesh