Re: [PATCH v3 34/40] mm: eliminate VMA_SPECIAL_FLAGS usage when hugetlb explicitly tested

[Lorenzo Stoakes (ARM)]

On Tue, Sep 29, 2026 at 10:42:00PM -0400, Zi Yan wrote:
> On Thu Sep 17, 2026 at 12:22 PM EDT, Lorenzo Stoakes (ARM) wrote:
> > It is now an invariant that VMA_IO_BIT is not set except by kernel-owned
> > mappings, so each existing VMA_SPECIAL_FLAGS test need only test for
> > VMA_DONTEXPAND_BIT, VMA_PFNMAP_BIT and VMA_MIXEDMAP_BIT.
> >
> > This is precisely a test for a kernel-owned or fixed mapping.
> >
> > Update a number of callsites which already explicitly handle hugetlb
> > mappings.
> >
> > vma_supports_mlock() and ksm_compatible() also explicitly bail on droppable
> > mappings - detecting kernel-owned, fixed or droppable mappings is handled
> > by vma_is_persistent(), so in these cases use this predicate.
> >
> > should_skip_vma() tests for locked, kernel-owned or fixed memory (having
> > already excluded hugetlb mappings) so simply test for those there.
> >
> > No functional change intended.
> >
> > Signed-off-by: Lorenzo Stoakes (ARM) <ljs@xxxxxxxxxx>
> > ---
> >  mm/internal.h | 4 +---
> >  mm/ksm.c      | 4 +---
> >  mm/vmscan.c   | 3 ++-
> >  3 files changed, 4 insertions(+), 7 deletions(-)
> >
>
> <snip>
>
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index 12ed3388ee41..09ff20c3df5b 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -3477,7 +3477,8 @@ static int should_skip_vma(unsigned long start, unsigned long end, struct mm_wal
> >  	if (!vma_has_recency(vma))
> >  		return true;
> >
> > -	if (vma->vm_flags & (VM_LOCKED | VM_SPECIAL))
> > +	if (vma_test(vma, VMA_LOCKED_BIT) || vma_is_kernel_owned(vma) ||
>
> At this point, mmap_lock is held, there is no mlock WIP, so
> VMA_LOCKED_BIT is enough.

Yes indeed :)

>
> > +	    vma_is_fixed_mapping(vma))
> >  		return true;
> >
> >  	if (vma == get_gate_vma(vma->vm_mm))
>
> LGTM.
>
> Reviewed-by: Zi Yan <ziy@xxxxxxxxxx>

Thanks!

>
>
> --
> Best Regards,
> Yan, Zi
>

--
Cheers, Lorenzo