Re: [PATCH v2 3/3] mm: use PF_ONLY_HEAD for PG_active and PG_unevictable

[Hugh Dickins]

On Mon, 1 Mar 2021, Yu Zhao wrote:
> On Mon, Mar 01, 2021 at 02:50:07PM +0300, Kirill A. Shutemov wrote:
> > On Fri, Feb 26, 2021 at 12:13:14PM +0000, Matthew Wilcox wrote:
> > > On Fri, Feb 26, 2021 at 02:17:18AM -0700, Yu Zhao wrote:
> > > > All places but one test, set or clear PG_active and PG_unevictable on
> > > > small or head pages. Use compound_head() explicitly for that singleton
> > > > so the rest can rid of redundant compound_head().
> > > 
> > > How do you know it's only one place?  I really wish you'd work with me
> > > on folios.  They make the compiler prove that it's not a tail page.
> > 
> > +1 to this.
> > 
> > The problem with compound_head() is systemic and ad-hoc solution to few
> > page flags will only complicate the picture.
> 
> Well, I call it an incremental improvement, and how exactly does it
> complicate the picture?
> 
> I see your point: you prefer a complete replacement. But my point is
> not about the preference; it's about presenting an option: I'm not
> saying we have to go with this series; I'm saying if you don't want
> to wait, here is something quick but not perfect.

+1 to this.

Hugh