Re: [-mm PATCH v2 00/25] get_user_pages() for dax pte and pmd mappings

From: Dan Williams <dan.j.williams@intel.com>
To: Jeff Moyer <jmoyer@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Dave Hansen <dave@sr71.net>, Toshi Kani <toshi.kani@hpe.com>,
	David Airlie <airlied@linux.ie>,
	Dave Hansen <dave.hansen@linux.intel.com>,
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	"H. Peter Anvin" <hpa@zytor.com>, Christoph Hellwig <hch@lst.de>,
	Andrea Arcangeli <aarcange@redhat.com>,
	kbuild test robot <lkp@intel.com>,
	linux-nvdimm <linux-nvdimm@ml01.01.org>,
	Richard Weinberger <richard@nod.at>, X86 ML <x86@kernel.org>,
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	Ingo Molnar <mingo@redhat.com>, Mel Gorman <mgorman@suse.de>,
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	Ross Zwisler <ross.zwisler@linux.intel.com>,
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	Jan Kara <jack@suse.com>, Paolo Bonzini <pbonzini@redhat.com>,
	Logan Gunthorpe <logang@deltatee.com>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [-mm PATCH v2 00/25] get_user_pages() for dax pte and pmd mappings
Date: Mon, 14 Dec 2015 08:44:02 -0800	[thread overview]
Message-ID: <CAPcyv4ju8BxtPzkC16jvS-C8QdWSU471KaPeyKNf7hdGF6HdqA@mail.gmail.com> (raw)
In-Reply-To: <x49lh8xccb8.fsf@segfault.boston.devel.redhat.com>

On Mon, Dec 14, 2015 at 6:52 AM, Jeff Moyer <jmoyer@redhat.com> wrote:
> Dan Williams <dan.j.williams@intel.com> writes:
>
>> In the meantime, I expect some would say DAX is a toy as long as it
>> continues to fail at DMA.
>
> I suppose this is the crux of it.  Given that we may be able to migrate
> away from the allocation of storage for temporary data structures in the
> future, and given that admin tooling could hide the undesirable
> configurations, this approach seems workable.

Here's my current thoughts on the tooling for namespace creation:

   ndctl create-namespace

That command by default will create a maximally sized pmem namespace
and set up the struct page memmap by default i.e. it defaults to the
following parameters:

    ndctl create-namespace --type=pmem --mode=memory

The other options for 'mode' are 'safe' and 'raw' where 'safe'
establishes a btt, and 'raw' exposes the full un-decorated capacity of
the namespace.

If you have a pre-existing 'raw' mode pmem namespace, you can convert
it to be enabled for dma, and other capabilities typical memory
possesses, with the following:

    ndctl create-namespace --mode=memory -r namespace0.0

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