Re: [PATCH -mm v2 06/11] pagewalk: add size to struct mm_walk

[Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>]

Hello Dave,

On Thu, Jun 12, 2014 at 03:07:11PM -0700, Dave Hansen wrote:
> On 06/12/2014 02:48 PM, Naoya Horiguchi wrote:
> > This variable is helpful if we try to share the callback function between
> > multiple slots (for example between pte_entry() and pmd_entry()) as done
> > in later patches.
> 
> smaps_pte() already does this:
> 
> static int smaps_pte(pte_t *pte, unsigned long addr, unsigned long end,
>                         struct mm_walk *walk)
> ...
>         unsigned long ptent_size = end - addr;
> 
> Other than the hugetlb handler, can't we always imply the size from
> end-addr?

Good point, thanks. I didn't care about this variable.

Currently we call this walk via walk_page_vma() so addr and end is
always between [vma->vm_start, vma->vm_end]. If a vma is not aligned
to pmd-boundary, this size might have incorrect value.
But using end-addr seems to cause no practical problem because in
such case first or final pmd never have a thp.
I'm not sure every caller (especially callers of walk_page_range())
assumes addr/end is page aligned, but walk->size approach looks safer
to me.

Thanks,
Naoya Horiguchi

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