Re: [PATCH v5 07/13] mm/khugepaged: add flag to ignore page young/referenced requirement

["Zach O'Keefe" <zokeefe@google.com>]

Thanks for the review, David!

On Thu, May 12, 2022 at 1:03 PM David Rientjes <rientjes@google.com> wrote:
>
> On Wed, 4 May 2022, Zach O'Keefe wrote:
>
> > Add enforce_young flag to struct collapse_control that allows context to
> > ignore requirement that some pages in region being collapsed be young or
> > referenced.  Set this flag in khugepaged collapse context to preserve
> > existing khugepaged behavior.
> >
> > This flag will be used (unset) when introducing madvise collapse
> > context since here, the user presumably has reason to believe the
> > collapse will be beneficial and khugepaged heuristics shouldn't tell
> > the user they are wrong.
> >
> > Signed-off-by: Zach O'Keefe <zokeefe@google.com>
> > ---
> >  mm/khugepaged.c | 23 +++++++++++++++--------
> >  1 file changed, 15 insertions(+), 8 deletions(-)
> >
> > diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> > index ca730aec0e3e..b14807b7002e 100644
> > --- a/mm/khugepaged.c
> > +++ b/mm/khugepaged.c
> > @@ -90,6 +90,9 @@ struct collapse_control {
> >       /* Respect khugepaged_max_ptes_[none|swap|shared] */
> >       bool enforce_pte_scan_limits;
> >
> > +     /* Require memory to be young */
> > +     bool enforce_young;
> > +
> >       /* Num pages scanned per node */
> >       int node_load[MAX_NUMNODES];
> >
>
> Small nit: is it possible to unify these into a single bool khugepaged
> flag?
>

I think this is fine with a "enforce_page_heuristics" flag or
something. Ofc, functionally unifying the flags is a noop, but I was
trying to to avoid "if (khugepagd) .. else .." and, where possible,
describe the variable properties of the collapse in struct
collapse_control itself. If there's no objections, I'll make that
change for v6.

> Either way:
>
> Acked-by: David Rientjes <rientjes@google.com>