Re: [PATCH mm-unstable v17 02/14] mm/khugepaged: generalize alloc_charge_folio()

[Nico Pache]

On Mon, May 18, 2026 at 8:50 AM Lance Yang <lance.yang@xxxxxxxxx> wrote:
>
>
>
> On 2026/5/18 19:55, Usama Arif wrote:
> [...]
> >> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> >> index 979885694351..f0e29d5c7b1f 100644
> >> --- a/mm/khugepaged.c
> >> +++ b/mm/khugepaged.c
> >> @@ -1068,21 +1068,26 @@ static enum scan_result __collapse_huge_page_swapin(struct mm_struct *mm,
> >>   }
> >>
> >>   static enum scan_result alloc_charge_folio(struct folio **foliop, struct mm_struct *mm,
> >> -            struct collapse_control *cc)
> >> +            struct collapse_control *cc, unsigned int order)
> >>   {
> >>      gfp_t gfp = (cc->is_khugepaged ? alloc_hugepage_khugepaged_gfpmask() :
> >>                   GFP_TRANSHUGE);
> >>      int node = collapse_find_target_node(cc);
> >>      struct folio *folio;
> >>
> >> -    folio = __folio_alloc(gfp, HPAGE_PMD_ORDER, node, &cc->alloc_nmask);
> >> +    folio = __folio_alloc(gfp, order, node, &cc->alloc_nmask);
> >>      if (!folio) {
> >>              *foliop = NULL;
> >> -            count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
> >> +            if (is_pmd_order(order))
> >> +                    count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
> >> +            count_mthp_stat(order, MTHP_STAT_COLLAPSE_ALLOC_FAILED);
> >>              return SCAN_ALLOC_HUGE_PAGE_FAIL;
> >>      }
> >>
> >> -    count_vm_event(THP_COLLAPSE_ALLOC);
> >> +    if (is_pmd_order(order))
> >> +            count_vm_event(THP_COLLAPSE_ALLOC);
> >> +    count_mthp_stat(order, MTHP_STAT_COLLAPSE_ALLOC);
> >> +
> >
> > The vmstat THP_COLLAPSE_ALLOC counter is pmd order only.
> > But after this we have
> >
> >       count_memcg_folio_events(folio, THP_COLLAPSE_ALLOC, 1);
> >
> > which is not being guarded with is_pmd_order().
>
> Good catch!
>
> >
> > I think we want this to be pmd order only as well so that
> > the meaning of the vmstat and cgroup counter remains the same?
>
> Agreed. THP_COLLAPSE_ALLOC should remain PMD order only for
> vmstat and memcg events.
>
> So this should be guarded with is_pmd_order() as well :)

Thanks Usama, I added that.

>
> Cheers, Lance
>