linux-kernel - Re: [HMM v13 05/18] mm/ZONE_DEVICE/devmem_pages_remove: allow early removal of device memory

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Date:   Mon, 21 Nov 2016 07:39:10 -0500
From:   Jerome Glisse <jglisse@...hat.com>
To:     Anshuman Khandual <khandual@...ux.vnet.ibm.com>
Cc:     akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, John Hubbard <jhubbard@...dia.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>
Subject: Re: [HMM v13 05/18] mm/ZONE_DEVICE/devmem_pages_remove: allow early
 removal of device memory

On Mon, Nov 21, 2016 at 04:07:46PM +0530, Anshuman Khandual wrote:
> On 11/18/2016 11:48 PM, Jérôme Glisse wrote:
> > HMM wants to remove device memory early before device tear down so add an
> > helper to do that.
> 
> Could you please explain why HMM wants to remove device memory before
> device tear down ?
> 

Some device driver want to manage memory for several physical devices from a
single fake device driver. Because it fits their driver architecture better
and those physical devices can have dedicated link between them.

Issue is that the fake device driver can outlive any of the real device for a
long time so we want to be able to remove device memory before the fake device
goes away to free up resources early.

Cheers,
Jérôme