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

Message ID 20211217113049.23850-4-david@redhat.com
State New
Headers show
Series mm: COW fixes part 1: fix the COW security issue for THP and hugetlb | expand

Commit Message

David Hildenbrand Dec. 17, 2021, 11:30 a.m. UTC 
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>
---
 mm/util.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)
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Patch

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;