On Wed, Jun 1, 2022 at 2:50 AM Michal Hocko <mhocko@xxxxxxxx> wrote:
>
> On Tue 31-05-22 16:47:49, Yang Shi wrote:
> > On Fri, May 27, 2022 at 2:46 AM Michal Hocko <mhocko@xxxxxxxx> wrote:
> [...]
> > > I really do not see any good reason to tightly couple kernel and user
> > > policies. Hints like MADV_{NO}HUGEPAGE are one thing and both kernel
> > > and userspace might decide to interpret them. But binding MADV_COLLAPSE
> > > to in kernel THP tunables just seems like pushing ourselves into the
> > > corner.
> >
> > I don't mean we should tightly couple kernel and user policies. I
> > think it is about how "never" is treated. AFAICT, typically sys admins
> > tend to expect "never" as a global switch and they don't expect any
> > THP allocation should happen in "never" mode even though it is
> > requested by the users. Maybe they should not expect so in the first
> > place.
>
> But this is not how the knob works, right? At least shmem has its own
> thing. So we do not have any global kill switch for transparent huge
> pages.
Yeah, but shmem has "never" mode too, which has the same semantics and
it is the default mode actually. Since MADV_COLLAPSE just collapse
anon memory for now, so the discussion was focused on anon THP. But
shmem is same.
And shmem even has "deny" mode which has stronger semantics.
>
> --
> Michal Hocko
> SUSE Labs
