Re: Thoughts on simple scanner approach for free page hinting

From: Michael S. Tsirkin
Date: Mon Apr 08 2019 - 22:44:31 EST

On Fri, Apr 05, 2019 at 05:09:45PM -0700, Alexander Duyck wrote:
> In addition we will need some way to identify which pages have been
> hinted on and which have not. The way I believe easiest to do this
> would be to overload the PageType value so that we could essentially
> have two values for "Buddy" pages. We would have our standard "Buddy"
> pages, and "Buddy" pages that also have the "Offline" value set in the
> PageType field. Tracking the Online vs Offline pages this way would
> actually allow us to do this with almost no overhead as the mapcount
> value is already being reset to clear the "Buddy" flag so adding a
> "Offline" flag to this clearing should come at no additional cost.

It bothers me a bit that this doesn't scale to multiple hint types
if we ever need them. Would it be better to have two
free lists: hinted and non-hinted one?