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Date: Mon, 7 May 2018 12:18:57 -0700
From: Matthew Wilcox <willy@infradead.org>
Subject: Re: [RFC PATCH v1 0/6] use mm to manage NVDIMM (pmem) zone
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To: Dan Williams <dan.j.williams@intel.com>
Cc: Huaisheng Ye <yehs1@lenovo.com>, Michal Hocko <mhocko@suse.com>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, linux-nvdimm <linux-nvdimm@lists.01.org>, Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>, chengnt@lenovo.com, pasha.tatashin@oracle.com, Sasha Levin <alexander.levin@verizon.com>, Linux MM <linux-mm@kvack.org>, Johannes Weiner <hannes@cmpxchg.org>, Andrew Morton <akpm@linux-foundation.org>, colyli@suse.de, Mel Gorman <mgorman@techsingularity.net>, Vlastimil Babka <vbabka@suse.cz>, Dave Hansen <dave.hansen@intel.com>

On Mon, May 07, 2018 at 11:57:10AM -0700, Dan Williams wrote:
> I think adding yet one more mm-zone is the wrong direction. Instead,
> what we have been considering is a mechanism to allow a device-dax
> instance to be given back to the kernel as a distinct numa node
> managed by the VM. It seems it times to dust off those patches.

I was wondering how "safe" we think that ability is.  NV-DIMM pages
(obviously) differ from normal pages by their non-volatility.  Do we
want their contents from the previous boot to be observable?  If not,
then we need the BIOS to clear them at boot-up, which means we would
want no kernel changes at all; rather the BIOS should just describe
those pages as if they were DRAM (after zeroing them).