Re: [PATCH v2 4/4] mm/mlock: migrate folios out of CMA when mlocking a range

[Lorenzo Stoakes <ljs@kernel.org>]

On Tue, Jul 07, 2026 at 09:36:17PM +0800, Wandun wrote:
<snip>
> > diff --git a/mm/mlock.c b/mm/mlock.c
> > index ac65de40b22b..f56c685533f5 100644
> > --- a/mm/mlock.c
> > +++ b/mm/mlock.c
<snip>
> > +static int mlock_collect_migratable_pte_range(pmd_t *pmd, unsigned long addr,
> > +			unsigned long end, struct mm_walk *walk)
> > +{
> > +	struct vm_area_struct *vma = walk->vma;
> > +	struct list_head *folio_list = walk->private;
> > +	spinlock_t *ptl;
> > +	pte_t *start_pte, *pte;
> > +	pte_t ptent;
> > +	struct folio *folio;
> > +	unsigned int step = 1;
> > +
> > +	if (!(vma->vm_flags & VM_LOCKED))
> > +		return 0;
> > +
> > +	ptl = pmd_trans_huge_lock(pmd, vma);
> > +	if (ptl) {
> > +		if (!pmd_present(*pmd)) {
> > +			if (unlikely(softleaf_is_migration(softleaf_from_pmd(*pmd)))) {
> > +				spin_unlock(ptl);
> > +				pmd_migration_entry_wait(vma->vm_mm, pmd);
> > +				walk->action = ACTION_AGAIN;
> > +				return 0;
> > +			}
> > +			goto out;
> > +		}
> > +		if (is_huge_zero_pmd(*pmd))
> > +			goto out;
> > +		folio = pmd_folio(*pmd);
> > +		if (folio_is_zone_device(folio))
> > +			goto out;
> > +		if (is_migrate_cma_page(&folio->page))
> > +			isolate_folio_to_list(folio, folio_list);
> > +		goto out;
> > +	}
> > +
> > +	start_pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
> > +	if (!start_pte) {
> > +		walk->action = ACTION_AGAIN;
> > +		return 0;
> > +	}
> > +
> > +	for (pte = start_pte; addr != end; pte += step, addr += step * PAGE_SIZE) {
> > +		step = 1;
> > +		ptent = ptep_get(pte);
> > +		if (!pte_present(ptent)) {
> > +			if (unlikely(softleaf_is_migration(softleaf_from_pte(ptent)))) {
> > +				pte_unmap_unlock(start_pte, ptl);
> > +				migration_entry_wait(vma->vm_mm, pmd, addr);
> > +				walk->action = ACTION_AGAIN;
> > +				return 0;
> > +			}
> > +			continue;
> > +		}
> > +		folio = vm_normal_folio(vma, addr, ptent);
> > +		if (!folio || folio_is_zone_device(folio))
> > +			continue;
> > +		step = folio_mlock_step(folio, pte, addr, end);
> > +		if (is_migrate_cma_page(&folio->page))
> Here should be, sorry about this.
> 	if (!is_migrate_cma_page(&folio->page))
> 		continue;

But above you do the:

		if (is_migrate_cma_page(&folio->page))
			isolate_folio_to_list(folio, folio_list);

Pattern :) so these should be consistent. But you're copy/pasting and need to
not do that so it's kind of by the by.

Anyway, yes I assumed you meant this. But see the main review, I am not really a
fan of the implementation, overall.

>
> Best regards
> Wandun

Thanks, Lorenzo