RFC: prepare for struct scatterlist entries without page backing

[Christoph Hellwig]

On Wed, Aug 12, 2015 at 03:42:47PM +0300, Boaz Harrosh wrote:
> The support I have suggested and submitted for zone-less sections.
> (In my add_persistent_memory() patchset)
>
> Would work perfectly well and transparent for all such multimedia cases.
> (All hacks removed). In fact I have loaded pmem (with-pages) on a VRAM
> a few times and it is great easy fun. (I wanted to experiment with cached
> memory over a pcie)

And everyone agree that it was both buggy and incomplete.

Dan has done a respin of the page backed nvdimm work with most of
these comments addressed.

I have to say I hate both pfn-based I/O [1] and page backed nvdimms with
passion, so we're looking into the lesser evil with an open mind.

[1] not the SGL part posted here, which I think is quite sane.  The bio
    side is much worse, though.