On Sat, 13 Mar 2021, Andrew Morton wrote: > On Fri, 5 Mar 2021 04:18:36 +0000 "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx> wrote: > > > Our type system does not currently distinguish between tail pages and > > head or single pages. This is a problem because we call compound_head() > > multiple times (and the compiler cannot optimise it out), bloating the > > kernel. It also makes programming hard as it is often unclear whether > > a function operates on an individual page, or an entire compound page. > > > > This patch series introduces the struct folio, which is a type that > > represents an entire compound page. This initial set reduces the kernel > > size by approximately 6kB, although its real purpose is adding > > infrastructure to enable further use of the folio. > > Geeze it's a lot of noise. More things to remember and we'll forever > have a mismash of `page' and `folio' and code everywhere converting > from one to the other. Ongoing addition of folio > accessors/manipulators to overlay the existing page > accessors/manipulators, etc. > > It's unclear to me that it's all really worth it. What feedback have > you seen from others? My own feeling and feedback have been much like yours. I don't get very excited by type safety at this level; and although I protested back when all those compound_head()s got tucked into the *PageFlag() functions, the text size increase was not very much, and I never noticed any adverse performance reports. To me, it's distraction, churn and friction, ongoing for years; but that's just me, and I'm resigned to the possibility that it will go in. Matthew is not alone in wanting to pursue it: let others speak. Hugh
