From: Arnd Bergmann <arnd@arndb.de>
To: Matthew Wilcox <willy@linux.intel.com>, Carsten Otte <cotte@de.ibm.com>
Subject: Re: NVM Mapping API
Date: Fri, 18 May 2012 09:33:49 +0000
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References: <20120515133450.GD22985@linux.intel.com>
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On Tuesday 15 May 2012, Matthew Wilcox wrote:
> 
> There are a number of interesting non-volatile memory (NVM) technologies
> being developed.  Some of them promise DRAM-comparable latencies and
> bandwidths.  At Intel, we've been thinking about various ways to present
> those to software.  This is a first draft of an API that supports the
> operations we see as necessary.  Patches can follow easily enough once
> we've settled on an API.
> 
> We think the appropriate way to present directly addressable NVM to
> in-kernel users is through a filesystem.  Different technologies may want
> to use different filesystems, or maybe some forms of directly addressable
> NVM will want to use the same filesystem as each other.

ext2 actually supports some of this already with mm/filemap_xip.c, Carsten
Otte introduced it initially to support drivers/s390/block/dcssblk.c with
execute-in-place, so you don't have to copy around the data when your
block device is mapped into the physical address space already.

I guess this could be implemented in modern file systems (ext4, btrfs)
as well, or you could have a new simple fs on top of the same base API.
(ext2+xip was originally a new file system but then merged into ext2).

Also note that you could easily implement non-volatile memory in other
virtual machines doing the same thing that dcssblk does: E.g. in KVM
you would only need to map a host file into the guess address space
and let the guest take advantage of a similar feature set that you
get from the new memory technologies in real hardware.

	Arnd
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