Re: [RFC PATCH 1/7] x86, mm: ZONE_DEVICE for "device memory"

[Dan Williams]

On Mon, Aug 17, 2015 at 2:45 PM, Jerome Glisse <j.glisse@xxxxxxxxx> wrote:
> On Fri, Aug 14, 2015 at 07:11:27PM -0700, Dan Williams wrote:
>> Although it does not offer perfect protection if device memory is at a
>> physically lower address than RAM, skipping the update of these
>> variables does seem to be what we want.  For example /dev/mem would
>> fail to allow write access to persistent memory if it fails a
>> valid_phys_addr_range() check.  Since /dev/mem does not know how to
>> write to PMEM in a reliably persistent way, it should not treat a
>> PMEM-pfn like RAM.
>
> So i attach is a patch that should keep ZONE_DEVICE out of consideration
> for the buddy allocator. You might also want to keep page reserved and not
> free inside the zone, you could replace the generic_online_page() using
> set_online_page_callback() while hotpluging device memory.
>

Hmm, are we already protected by the fact that ZONE_DEVICE is not
represented in the GFP_ZONEMASK?
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