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SubjectRe: [PATCH V2] mm/mprotect: Add a cond_resched() inside change_pmd_range()
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?

> diff --git a/mm/mprotect.c b/mm/mprotect.c
> index ec39f73..3d445ee 100644
> --- a/mm/mprotect.c
> +++ b/mm/mprotect.c
> @@ -188,7 +188,7 @@ static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
> }
>
> /* huge pmd was handled */
> - continue;
> + goto next;
> }
> }
> /* fall through, the trans huge pmd just split */
> @@ -196,6 +196,8 @@ 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;
> +next:
> + cond_resched();
> } while (pmd++, addr = next, addr != end);
>
> if (mni_start)

--
Michal Hocko
SUSE Labs

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