Re: [Linux-nvdimm] another pmem variant

[Christoph Hellwig <hch@lst.de>]

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.