Re: [PATCH v1 03/11] mm: simplify hugetlb and file-THP handling in __page_mapcount()

On Fri, Dec 17, 2021 at 3:33 AM David Hildenbrand david@redhat.com 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.

Reviewed-by: Peter Xu peterx@redhat.com Signed-off-by: David Hildenbrand david@redhat.com

Reviewed-by: Yang Shi shy828301@gmail.com

---

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);
    /*
     * For file THP page->_mapcount contains total number of mapping
     * of the page: no need to look into compound_mapcount.
     */
  

•   if (!PageAnon(page) && !PageHuge(page))
  

•           return ret;
  

•   if (!PageAnon(page))
  

•           return atomic_read(&page->_mapcount) + 1;
  

•   ret = atomic_read(&page->_mapcount) + 1;
    page = compound_head(page);
  

•   ret += atomic_read(compound_mapcount_ptr(page)) + 1;
  

•   ret += head_compound_mapcount(page);
    if (PageDoubleMap(page))
            ret--;
    return ret;
  

-- 2.31.1