Re: [PATCH v2 1/5] mm/hugetlb: fix races when looking up a CONT-PTE size hugetlb page

[Baolin Wang]

On 8/25/2022 3:10 PM, David Hildenbrand wrote:
> > > +		/*
> > > +		 * try_grab_page() should always succeed here, because we hold
> > > +		 * the ptl lock and have verified pte_present().
> > > +		 */
> > > +		if (WARN_ON_ONCE(!try_grab_page(page, flags))) {
> > > +			page = NULL;
> > > +			goto out;
> > > +		}
> > > +	} else {
> >
> > Should add FOLL_MIGRATION validation before waiting a migration entry.
>
> We really only need FOLL_MIGRATION for KSM. As hugetlb pages cannot be
> KSM pages, we don't need this.
>
> Actually, I do have patches in the works that rip out FOLL_MIGRATION
> completely by adjusting KSM code.
>
> So let's try to not add dead code (although it would make sense for
> feature completeness as is -- but then, FOLL_MIGRATION really needs to go).

Make sense. Thanks for your explanation.