On 01/27/23 15:04, Andrew Morton wrote:
> On Fri, 27 Jan 2023 17:23:39 +0100 David Hildenbrand <david@xxxxxxxxxx> wrote:
>
> > On 26.01.23 23:27, Mike Kravetz wrote:
> > > A hugetlb page will have a mapcount of 1 if mapped by multiple processes
> > > via a shared PMD. This is because only the first process increases the
> > > map count, and subsequent processes just add the shared PMD page to
> > > their page table.
> > >
> > > page_mapcount is being used to decide if a hugetlb page is shared or
> > > private in /proc/PID/smaps. Pages referenced via a shared PMD were
> > > incorrectly being counted as private.
> > >
> > > To fix, check for a shared PMD if mapcount is 1. If a shared PMD is
> > > found count the hugetlb page as shared. A new helper to check for a
> > > shared PMD is added.
> > >
> > ...
> >
> > > --- a/fs/proc/task_mmu.c
> > > +++ b/fs/proc/task_mmu.c
> > > @@ -749,8 +749,14 @@ static int smaps_hugetlb_range(pte_t *pte, unsigned long hmask,
> > >
> > > if (mapcount >= 2)
> > > mss->shared_hugetlb += huge_page_size(hstate_vma(vma));
> > > - else
> > > - mss->private_hugetlb += huge_page_size(hstate_vma(vma));
> > > + else {
> >
> > Better:
> >
> > if (mapcount >= 2 || hugetlb_pmd_shared(pte))
> > mss->shared_hugetlb += huge_page_size(hstate_vma(vma));
> > else
> > mss->private_hugetlb += huge_page_size(hstate_vma(vma));
>
> Yup. And that local doesn't add any value?
>
> --- a/fs/proc/task_mmu.c~mm-hugetlb-proc-check-for-hugetlb-shared-pmd-in-proc-pid-smaps-fix
> +++ a/fs/proc/task_mmu.c
> @@ -745,18 +745,10 @@ static int smaps_hugetlb_range(pte_t *pt
> page = pfn_swap_entry_to_page(swpent);
> }
> if (page) {
> - int mapcount = page_mapcount(page);
> -
> - if (mapcount >= 2)
> + if (page_mapcount(page) >= 2 || hugetlb_pmd_shared(pte))
> mss->shared_hugetlb += huge_page_size(hstate_vma(vma));
> - else {
> - if (hugetlb_pmd_shared(pte))
> - mss->shared_hugetlb +=
> - huge_page_size(hstate_vma(vma));
> - else
> - mss->private_hugetlb +=
> - huge_page_size(hstate_vma(vma));
> - }
> + else
> + mss->private_hugetlb += huge_page_size(hstate_vma(vma));
> }
> return 0;
> }
Thank you both! That looks much better.
--
Mike Kravetz
