Re: [PATCH 1/2] mm: hugetlb: proc: check for hugetlb shared PMD in /proc/PID/smaps

[David Hildenbrand]

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.
>
> Fixes: 25ee01a2fca0 ("mm: hugetlb: proc: add hugetlb-related fields to /proc/PID/smaps")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> ---
>   fs/proc/task_mmu.c      | 10 ++++++++--
>   include/linux/hugetlb.h | 12 ++++++++++++
>   2 files changed, 20 insertions(+), 2 deletions(-)
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index e35a0398db63..cb9539879402 100644
> --- 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));



--
Thanks,

David / dhildenb