Re: [PATCH v12 2/5] fs/proc/task_mmu: Implement IOCTL to get and optionally clear info about PTEs

["Michał Mirosław" <emmir@google.com>]

On Thu, 6 Apr 2023 at 09:40, Muhammad Usama Anjum
<usama.anjum@collabora.com> wrote:
[...]
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
[...]
> +static int pagemap_scan_pmd_entry(pmd_t *pmd, unsigned long start,
> +                                 unsigned long end, struct mm_walk *walk)
> +{
> +       struct pagemap_scan_private *p = walk->private;
> +       bool is_written, is_file, is_present, is_swap;
> +       struct vm_area_struct *vma = walk->vma;
> +       unsigned long addr = end;
> +       spinlock_t *ptl;
> +       int ret = 0;
> +       pte_t *pte;
> +
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +       ptl = pmd_trans_huge_lock(pmd, vma);
> +       if (ptl) {
[...]
> +               return ret;
> +       }
> +process_smaller_pages:
> +       if (pmd_trans_unstable(pmd))
> +               return 0;

Why pmd_trans_unstable() is needed here and not only after split_huge_pmd()?

Best regards
Michał Mirosław