Re: Phyr Starter

[Jason Gunthorpe]

On Tue, Jan 11, 2022 at 02:01:17PM +0000, Matthew Wilcox wrote:
> On Tue, Jan 11, 2022 at 12:17:18AM -0800, John Hubbard wrote:
> > Zooming in on the pinning aspect for a moment: last time I attempted to
> > convert O_DIRECT callers from gup to pup, I recall wanting very much to
> > record, in each bio_vec, whether these pages were acquired via FOLL_PIN,
> > or some non-FOLL_PIN method. Because at the end of the IO, it is not
> > easy to disentangle which pages require put_page() and which require
> > unpin_user_page*().
> > 
> > And changing the bio_vec for *that* purpose was not really acceptable.
> > 
> > But now that you're looking to change it in a big way (and with some
> > spare bits avaiable...oohh!), maybe I can go that direction after all.
> > 
> > Or, are you looking at a design in which any phyr is implicitly FOLL_PIN'd
> > if it exists at all?
> 
> That.  I think there's still good reasons to keep a single-page (or
> maybe dual-page) GUP around, but no reason to mix it with ranges.
> 
> > Or any other thoughts in this area are very welcome.
> 
> That's there's no support for unpinning part of a range.  You pin it,
> do the IO, unpin it.  That simplifies the accounting.

VFIO wouldn't like this :(

Jason