[patch 052/147] mm: remove redundant compound_head() calling

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From: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Subject: mm: remove redundant compound_head() calling

There is a READ_ONCE() in the macro of compound_head(), which will prevent
compiler from optimizing the code when there are more than once calling of
it in a function.  Remove the redundant calling of compound_head() from
page_to_index() and page_add_file_rmap() for better code generation.

Link: https://lkml.kernel.org/r/20210811101431.83940-1-songmuchun@xxxxxxxxxxxxx
Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Reviewed-by: David Howells <dhowells@xxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: William Kucharski <william.kucharski@xxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 include/linux/pagemap.h |    7 +++----
 mm/rmap.c               |    6 ++++--
 2 files changed, 7 insertions(+), 6 deletions(-)

--- a/include/linux/pagemap.h~mm-remove-redundant-compound_head-calling
+++ a/include/linux/pagemap.h
@@ -521,18 +521,17 @@ static inline struct page *read_mapping_
  */
 static inline pgoff_t page_to_index(struct page *page)
 {
-	pgoff_t pgoff;
+	struct page *head;
 
 	if (likely(!PageTransTail(page)))
 		return page->index;
 
+	head = compound_head(page);
 	/*
 	 *  We don't initialize ->index for tail pages: calculate based on
 	 *  head page
 	 */
-	pgoff = compound_head(page)->index;
-	pgoff += page - compound_head(page);
-	return pgoff;
+	return head->index + page - head;
 }
 
 extern pgoff_t hugetlb_basepage_index(struct page *page);
--- a/mm/rmap.c~mm-remove-redundant-compound_head-calling
+++ a/mm/rmap.c
@@ -1230,11 +1230,13 @@ void page_add_file_rmap(struct page *pag
 						nr_pages);
 	} else {
 		if (PageTransCompound(page) && page_mapping(page)) {
+			struct page *head = compound_head(page);
+
 			VM_WARN_ON_ONCE(!PageLocked(page));
 
-			SetPageDoubleMap(compound_head(page));
+			SetPageDoubleMap(head);
 			if (PageMlocked(page))
-				clear_page_mlock(compound_head(page));
+				clear_page_mlock(head);
 		}
 		if (!atomic_inc_and_test(&page->_mapcount))
 			goto out;
_




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