> On Dec 17, 2021, at 3:30 AM, David Hildenbrand <david@xxxxxxxxxx> wrote:
>
> Let's return early for hugetlb, which really only relies on the compound
> mapcount so far and does not support PageDoubleMap() yet. Use the chance
> to cleanup the file-THP case to make it easier to grasp. While at it, use
> head_compound_mapcount().
>
> This is a preparation for further changes.
It would be useful to add “no functional change intended” or something.
>
> Reviewed-by: Peter Xu <peterx@xxxxxxxxxx>
> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
> ---
> mm/util.c | 11 +++++++----
> 1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/mm/util.c b/mm/util.c
> index 741ba32a43ac..3239e75c148d 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -732,15 +732,18 @@ int __page_mapcount(struct page *page)
> {
> int ret;
>
> - ret = atomic_read(&page->_mapcount) + 1;
> + if (PageHuge(page))
> + return compound_mapcount(page);
Before you return, perhaps you can add an assertion like:
VM_BUG_ON(PageDoubleMap(page));
This would be make the code clearer and would ease debugging in the
future (if support for double-map is expanded).
