Re: [PATCH v2 1/7] mm: factor out generic PTE batch detection from swap_pte_batch()

On Thu, 2026-08-13 at 11:57 +0200, David Hildenbrand (Arm) wrote:
> On 8/13/26 06:23, Shivank Garg wrote:
> > Factor out the generic PTE batch detection logic from swap_pte_batch()
> > into softleaf_pte_batch() helper, so that it can be reused by upcoming
> > patch that adds restore-side batching of migration entries.
> > 
> > swap_pte_batch() now keeps only its swap-specific concerns and
> > delegates the batch detection to softleaf_pte_batch().
> > 
> > No functional changes intended.
> > 
> > Signed-off-by: Shivank Garg <[email protected]>
> > ---
> >  mm/internal.h | 36 +++++++++++++++++++++---------------
> >  1 file changed, 21 insertions(+), 15 deletions(-)
> > 
> > diff --git a/mm/internal.h b/mm/internal.h
> > index a5d0488a54dc..1e1ab53b642e 100644
> > --- a/mm/internal.h
> > +++ b/mm/internal.h
> > @@ -560,6 +560,26 @@ static inline void set_softleaf_ptes(struct mm_struct *mm, unsigned long addr,
> >  	}
> >  }
> >  
> > +static inline int softleaf_pte_batch(pte_t *start_ptep, int max_nr, pte_t pte)
> > +{
> > +	pte_t expected_pte = pte_next_softleaf_offset(pte);
> > +	const pte_t *end_ptep = start_ptep + max_nr;
> > +	pte_t *ptep = start_ptep + 1;
> > +
> 
> Wouldn't we want some way to make sure that the softleaf entries actually carry
> offsets or pfns of sorts?
> 
> > +	VM_WARN_ON(max_nr < 1);
> > +
> > +	while (ptep < end_ptep) {
> > +		pte = ptep_get(ptep);
> > +
> > +		if (!pte_same(pte, expected_pte))
> > +			break;
> > +		expected_pte = pte_next_softleaf_offset(expected_pte);
> > +		ptep++;
> > +	}
> > +
> > +	return ptep - start_ptep;
> > +}
> > +
> >  /**
> >   * swap_pte_batch - detect a PTE batch for a set of contiguous swap entries
> >   * @start_ptep: Page table pointer for the first entry.
> > @@ -577,23 +597,9 @@ static inline void set_softleaf_ptes(struct mm_struct *mm, unsigned long addr,
> >   */
> >  static inline int swap_pte_batch(pte_t *start_ptep, int max_nr, pte_t pte)
> >  {
> > -	pte_t expected_pte = pte_next_softleaf_offset(pte);
> > -	const pte_t *end_ptep = start_ptep + max_nr;
> > -	pte_t *ptep = start_ptep + 1;
> > -
> > -	VM_WARN_ON(max_nr < 1);
> >  	VM_WARN_ON(!softleaf_is_swap(softleaf_from_pte(pte)));
> 
> Any reason we cannot simply rename this thing and drop the VM_WARN_ON? I mean, a
> caller can just do that.
> 

Thanks David,

Agreed on both suggestions.

I'll add VM_WARN_ON(!softleaf_is_swap(entry) && !softleaf_has_pfn(entry))
in softleaf_pte_batch() for making sure it has offset/pfn and remove
swap_pte_batch().

Best regards,
Shivank