On Fri, 27 Jan 2023 17:23:39 +0100 David Hildenbrand david@redhat.com 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));
elsemss->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; } _