On Sun, Mar 21, 2021 at 07:45:28PM +0100, Thomas Hellström (Intel) wrote: > diff --git a/mm/gup.c b/mm/gup.c > index e40579624f10..1b6a127f0bdd 100644 > +++ b/mm/gup.c > @@ -1993,6 +1993,17 @@ static void __maybe_unused undo_dev_pagemap(int *nr, int nr_start, > } > > #ifdef CONFIG_ARCH_HAS_PTE_SPECIAL > +/* > + * If we can't determine whether or not a pte is special, then fail immediately > + * for ptes. Note, we can still pin HugeTLB as it is guaranteed not to be > + * special. For THP, special huge entries are indicated by xxx_devmap() > + * returning true, but a corresponding call to get_dev_pagemap() will > + * return NULL. > + * > + * For a futex to be placed on a THP tail page, get_futex_key requires a > + * get_user_pages_fast_only implementation that can pin pages. Thus it's still > + * useful to have gup_huge_pmd even if we can't operate on ptes. > + */ Why move this comment? I think it was correct where it was Jason
