Re: [PATCH] mm: mempolicy: don't have to split pmd for huge zero page

[Yang Shi]

On Tue, Jun 8, 2021 at 10:49 AM Michal Hocko <mhocko@xxxxxxxx> wrote:
>
> On Tue 08-06-21 10:15:36, Yang Shi wrote:
> [...]
> > I did some archeology, the findings are:
> >
> > The zero page has PageReserved flag set, it was skipped by the
> > explicit PageReserved check in mempolicy.c since commit f4598c8b3678
> > ("[PATCH] migration: make sure there is no attempt to migrate reserved
> > pages."). The zero page was not used anymore by do_anonymous_page()
> > since 2.6.24 by commit 557ed1fa2620 ("remove ZERO_PAGE"), then
> > reinstated by commit a13ea5b759645 ("mm: reinstate ZERO_PAGE") and
> > this commit added zero page check in vm_normal_page(), so mempolicy
> > doesn't depend on PageReserved check to skip zero page anymore since
> > then.
> >
> > So the zero page is skipped by mempolicy.c since 2.6.16.
>
> Thanks a lot! This is really useful. Can you just add it to the
> changelog so others do not have to go through the painful archeology.
>
> With that, feel free to add
> Acked-by: Michal Hocko <mhocko@xxxxxxxx>

Thanks. Will add that into v2.

>
> Thanls!
> --
> Michal Hocko
> SUSE Labs