On Thu 14-12-17 18:50:41, Anshuman Khandual wrote: > On 12/14/2017 06:34 PM, Michal Hocko wrote: > > On Thu 14-12-17 18:25:54, Anshuman Khandual wrote: > >> On 12/14/2017 04:59 PM, Michal Hocko wrote: > >>> On Thu 14-12-17 16:44:26, Anshuman Khandual wrote: > >>>> diff --git a/mm/mprotect.c b/mm/mprotect.c > >>>> index ec39f73..43c29fa 100644 > >>>> --- a/mm/mprotect.c > >>>> +++ b/mm/mprotect.c > >>>> @@ -196,6 +196,7 @@ static inline unsigned long change_pmd_range(struct > >>>> vm_area_struct *vma, > >>>> this_pages = change_pte_range(vma, pmd, addr, next, > >>>> newprot, > >>>> dirty_accountable, prot_numa); > >>>> pages += this_pages; > >>>> + cond_resched(); > >>>> } while (pmd++, addr = next, addr != end); > >>>> > >>>> if (mni_start) > >>> this is not exactly what I meant. See how change_huge_pmd does continue. > >>> That's why I mentioned zap_pmd_range which does goto next... > >> I might be still missing something but is this what you meant ? > > yes, except > > > >> Here we will give cond_resched() cover to the THP backed pages > >> as well. > > but there is still > > if (!is_swap_pmd(*pmd) && !pmd_trans_huge(*pmd) && > > !pmd_devmap(*pmd) > > && pmd_none_or_clear_bad(pmd)) > > continue; > > > > so we won't have scheduling point on pmd holes. Maybe this doesn't > > matter, I haven't checked but why should we handle those differently? > > May be because it is not spending much time for those entries which > can really trigger stalls, hence they dont need scheduling points. > In case of zap_pmd_range(), it was spending time either in > __split_huge_pmd() or zap_huge_pmd() hence deserved a scheduling point.
As I've said, I haven't thought much about that but the discrepancy just hit my eyes. So if there is not a really good reason I would rather use goto next consistently. -- Michal Hocko SUSE Labs
