On Sat, Mar 13, 2021 at 07:09:01PM -0800, Hugh Dickins wrote: > 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. I'm with Matthew on this. I would really want to drop the number of places where we call compoud_head(). I hope we can get rid of the page flag policy hack I made. -- Kirill A. Shutemov
