linux-kernel - Re: [Linux-nvdimm] another pmem variant

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Date:	Wed, 25 Mar 2015 17:44:28 +0100
From:	Christoph Hellwig <hch@....de>
To:	Dan Williams <dan.j.williams@...el.com>
Cc:	Christoph Hellwig <hch@....de>,
	linux-nvdimm <linux-nvdimm@...1.01.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	X86 ML <x86@...nel.org>, Jens Axboe <axboe@...nel.dk>
Subject: Re: [Linux-nvdimm] another pmem variant

On Wed, Mar 25, 2015 at 09:33:52AM -0700, Dan Williams wrote:
> This is mostly ok and does not collide too much with the upcoming ACPI
> mechanism for this stuff.  I do worry that the new
> "memmap=nn[KMG]!ss[KMG]" kernel command line option will only be
> relevant for at most one kernel cycle given the imminent publication
> of the spec that unblocks our release.

I don't think we can just get rid of it as legacy systems won't be
upgraded to the new discovery mechanism.  Or do you mean you plan to
introduce a better override on the command line?  In that case speak
up now!

> Our planned solution to the "legacy pmem" problem is to have a
> userspace utility craft a list of address ranges in the form that ACPI
> expects and attach that to a platform device (one time setup).  It
> only requires that the memory be marked reserved, not necessarily
> marked type-12.

I can't see any benefit of that over just doign the right thing in
kernel space.

> > The other two patches are a heavily rewritten version of the code that
> > Intel gave to various storage vendors to discover the type 12 (and earlier
> > type 6) nvdimms, which I massaged into a form that is hopefully suitable
> > for mainline.
> 
> I'd prefer E820_PMEM over E820_PROTECTED_KERN, I don't know why I
> chose that name initially, but to each his own bike shed.

Sounds fine to me.
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