linux-kernel - Re: [RFC PATCH 1/7] x86, mm: ZONE

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Date:	Mon, 17 Aug 2015 17:46:43 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Jerome Glisse <j.glisse@...il.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Boaz Harrosh <boaz@...xistor.com>,
	Rik van Riel <riel@...hat.com>,
	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	david <david@...morbit.com>, Ingo Molnar <mingo@...nel.org>,
	Linux MM <linux-mm@...ck.org>, Ingo Molnar <mingo@...hat.com>,
	Mel Gorman <mgorman@...e.de>, "H. Peter Anvin" <hpa@...or.com>,
	Ross Zwisler <ross.zwisler@...ux.intel.com>,
	"torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
	Christoph Hellwig <hch@....de>
Subject: Re: [RFC PATCH 1/7] x86, mm: ZONE_DEVICE for "device memory"

On Mon, Aug 17, 2015 at 2:45 PM, Jerome Glisse <j.glisse@...il.com> 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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