mm: simplify calling a compound page destructor

None of the three callers of get_compound_page_dtor() want to know the
value; they just want to call the function.  Replace it with
destroy_compound_page() which calls the dtor for them.
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Link: http://lkml.kernel.org/r/20200517105051.9352-1-willy@infradead.orgSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/mm.h

@@ -876,10 +876,10 @@ static inline void set_compound_page_dtor(struct page *page,
 	page[1].compound_dtor = compound_dtor;
 }
 
-static inline compound_page_dtor *get_compound_page_dtor(struct page *page)
+static inline void destroy_compound_page(struct page *page)
 {
 	VM_BUG_ON_PAGE(page[1].compound_dtor >= NR_COMPOUND_DTORS, page);
-	return compound_page_dtors[page[1].compound_dtor];
+	compound_page_dtors[page[1].compound_dtor](page);
 }
 
 static inline unsigned int compound_order(struct page *page)

mm/swap.c

@@ -102,8 +102,6 @@ static void __put_single_page(struct page *page)
 
 static void __put_compound_page(struct page *page)
 {
-	compound_page_dtor *dtor;
-
 	/*
 	 * __page_cache_release() is supposed to be called for thp, not for
 	 * hugetlb. This is because hugetlb page does never have PageLRU set
@@ -112,8 +110,7 @@ static void __put_compound_page(struct page *page)
 	 */
 	if (!PageHuge(page))
 		__page_cache_release(page);
-	dtor = get_compound_page_dtor(page);
-	(*dtor)(page);
+	destroy_compound_page(page);
 }
 
 void __put_page(struct page *page)

mm/vmscan.c

@@ -1438,7 +1438,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 		 * appear not as the counts should be low
 		 */
 		if (unlikely(PageTransHuge(page)))
-			(*get_compound_page_dtor(page))(page);
+			destroy_compound_page(page);
 		else
 			list_add(&page->lru, &free_pages);
 		continue;
@@ -1859,7 +1859,7 @@ static unsigned noinline_for_stack move_pages_to_lru(struct lruvec *lruvec,
 
 			if (unlikely(PageCompound(page))) {
 				spin_unlock_irq(&pgdat->lru_lock);
-				(*get_compound_page_dtor(page))(page);
+				destroy_compound_page(page);
 				spin_lock_irq(&pgdat->lru_lock);
 			} else
 				list_add(&page->lru, &pages_to_free);