On Thu, Jun 6, 2024 at 5:41 PM David Hildenbrand <david@xxxxxxxxxx> wrote: > > On 06.06.24 11:38, Lance Yang wrote: > > On Thu, Jun 6, 2024 at 4:06 PM David Hildenbrand <david@xxxxxxxxxx> wrote: > >> > >> On 06.06.24 10:01, David Hildenbrand wrote: > >>> On 06.06.24 05:55, Lance Yang wrote: > >>>> On Wed, Jun 5, 2024 at 10:28 PM David Hildenbrand <david@xxxxxxxxxx> wrote: > >>>>> > >>>>> On 05.06.24 16:20, Lance Yang wrote: > >>>>>> Hi David, > >>>>>> > >>>>>> On Wed, Jun 5, 2024 at 8:46 PM David Hildenbrand <david@xxxxxxxxxx> wrote: > >>>>>>> > >>>>>>> On 21.05.24 06:02, Lance Yang wrote: > >>>>>>>> In preparation for supporting try_to_unmap_one() to unmap PMD-mapped > >>>>>>>> folios, start the pagewalk first, then call split_huge_pmd_address() to > >>>>>>>> split the folio. > >>>>>>>> > >>>>>>>> Since TTU_SPLIT_HUGE_PMD will no longer perform immediately, we might > >>>>>>>> encounter a PMD-mapped THP missing the mlock in the VM_LOCKED range during > >>>>>>>> the page walk. It’s probably necessary to mlock this THP to prevent it from > >>>>>>>> being picked up during page reclaim. > >>>>>>>> > >>>>>>>> Suggested-by: David Hildenbrand <david@xxxxxxxxxx> > >>>>>>>> Suggested-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx> > >>>>>>>> Signed-off-by: Lance Yang <ioworker0@xxxxxxxxx> > >>>>>>>> --- > >>>>>>> > >>>>>>> [...] again, sorry for the late review. > >>>>>> > >>>>>> No worries at all, thanks for taking time to review! > >>>>>> > >>>>>>> > >>>>>>>> diff --git a/mm/rmap.c b/mm/rmap.c > >>>>>>>> index ddffa30c79fb..08a93347f283 100644 > >>>>>>>> --- a/mm/rmap.c > >>>>>>>> +++ b/mm/rmap.c > >>>>>>>> @@ -1640,9 +1640,6 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, > >>>>>>>> if (flags & TTU_SYNC) > >>>>>>>> pvmw.flags = PVMW_SYNC; > >>>>>>>> > >>>>>>>> - if (flags & TTU_SPLIT_HUGE_PMD) > >>>>>>>> - split_huge_pmd_address(vma, address, false, folio); > >>>>>>>> - > >>>>>>>> /* > >>>>>>>> * For THP, we have to assume the worse case ie pmd for invalidation. > >>>>>>>> * For hugetlb, it could be much worse if we need to do pud > >>>>>>>> @@ -1668,20 +1665,35 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, > >>>>>>>> mmu_notifier_invalidate_range_start(&range); > >>>>>>>> > >>>>>>>> while (page_vma_mapped_walk(&pvmw)) { > >>>>>>>> - /* Unexpected PMD-mapped THP? */ > >>>>>>>> - VM_BUG_ON_FOLIO(!pvmw.pte, folio); > >>>>>>>> - > >>>>>>>> /* > >>>>>>>> * If the folio is in an mlock()d vma, we must not swap it out. > >>>>>>>> */ > >>>>>>>> if (!(flags & TTU_IGNORE_MLOCK) && > >>>>>>>> (vma->vm_flags & VM_LOCKED)) { > >>>>>>>> /* Restore the mlock which got missed */ > >>>>>>>> - if (!folio_test_large(folio)) > >>>>>>>> + if (!folio_test_large(folio) || > >>>>>>>> + (!pvmw.pte && (flags & TTU_SPLIT_HUGE_PMD))) > >>>>>>>> mlock_vma_folio(folio, vma); > > > > Should we still keep the '!pvmw.pte' here? Something like: > > > > if (!folio_test_large(folio) || !pvmw.pte) > > mlock_vma_folio(folio, vma); > > I was wondering the same the whole time ... > > > > > We can mlock the THP to prevent it from being picked up during page reclaim. > > > > David, I’d like to hear your thoughts on this ;) > > but I think there is no need to for now, in the context of your patchset. :) Agreed. Let's drop it for now :) Thanks a lot for your thoughts! Lance > > -- > Cheers, > > David / dhildenb >