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Date: Mon, 23 Mar 2015 13:59:53 -0700
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Subject: Re: [PATCH 7/8] pmem: Add support for page structs
From: Dan Williams <dan.j.williams@intel.com>
To: Boaz Harrosh <boaz@plexistor.com>
Cc: Ingo Molnar <mingo@redhat.com>, X86 ML <x86@kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        "Roger C. Pao" <rcpao.enmotus@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        linux-nvdimm <linux-nvdimm@ml01.01.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Matthew Wilcox <willy@linux.intel.com>,
        Andy Lutomirski <luto@amacapital.net>,
        Christoph Hellwig <hch@infradead.org>,
        Ross Zwisler <ross.zwisler@linux.intel.com>
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On Thu, Mar 5, 2015 at 3:59 AM, Boaz Harrosh <boaz@plexistor.com> wrote:
>
> One of the current shortcomings of the NVDIMM/PMEM
> support is that this memory does not have a page-struct(s)
> associated with its memory and therefor cannot be passed
> to a block-device or network or DMAed in any way through
> another device in the system.
>
> The use of add_persistent_memory() fixes all this. After this patch
> an FS can do:
>         bdev_direct_access(,&pfn,);

Hmm, can we do this mapping on demand per direct access mapping rather
than unconditionally for each range that pmem is handling?

Going forward I don't think we want to be tied to guaranteeing that
plain bdev_direct_access() always yields pfn_to_page()-capable pfns.

Perhaps a DAX_MAP_PFN flag or something along those lines?