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Date: Mon, 17 Aug 2015 17:46:43 -0700
Message-ID: <CAPcyv4jPezPAy9gMMtenBH1U526N3cwQY02823jfqWPyuRMouw@mail.gmail.com>
Subject: Re: [RFC PATCH 1/7] x86, mm: ZONE_DEVICE for "device memory"
From: Dan Williams <dan.j.williams@intel.com>
To: Jerome Glisse <j.glisse@gmail.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Boaz Harrosh <boaz@plexistor.com>, Rik van Riel <riel@redhat.com>,
        "linux-nvdimm@lists.01.org" <linux-nvdimm@ml01.01.org>,
        Dave Hansen <dave.hansen@linux.intel.com>, david <david@fromorbit.com>,
        Ingo Molnar <mingo@kernel.org>, Linux MM <linux-mm@kvack.org>,
        Ingo Molnar <mingo@redhat.com>, Mel Gorman <mgorman@suse.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Ross Zwisler <ross.zwisler@linux.intel.com>,
        "torvalds@linux-foundation.org" <torvalds@linux-foundation.org>,
        Christoph Hellwig <hch@lst.de>
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On Mon, Aug 17, 2015 at 2:45 PM, Jerome Glisse <j.glisse@gmail.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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