[RFC PATCH] mm: drop mark_page_access from the unmap path

[Michal Hocko]

On Tue 06-08-19 19:55:09, Minchan Kim wrote:
> On Wed, Jul 31, 2019 at 09:21:01AM +0200, Michal Hocko wrote:
> > On Wed 31-07-19 14:44:47, Minchan Kim wrote:
[...]
> > > As Nick mentioned in the description, without mark_page_accessed in
> > > zapping part, repeated mmap + touch + munmap never acticated the page
> > > while several read(2) calls easily promote it.
> > 
> > And is this really a problem? If we refault the same page then the
> > refaults detection should catch it no? In other words is the above still
> > a problem these days?
> 
> I admit we have been not fair for them because read(2) syscall pages are
> easily promoted regardless of zap timing unlike mmap-based pages.
> 
> However, if we remove the mark_page_accessed in the zap_pte_range, it
> would make them more unfair in that read(2)-accessed pages are easily
> promoted while mmap-based page should go through refault to be promoted.

I have really hard time to follow why an unmap special handling is
making the overall state more reasonable.

Anyway, let me throw the patch for further discussion. Nick, Mel,
Johannes what do you think?