[PATCH 04/19] mm: avoid PG_locked on tail pages

[Kirill A. Shutemov]

With new refcounting pte entries can point to tail pages. It's doesn't
make much sense to mark tail page locked -- we need to protect whole
compound page.

This patch adjust helpers related to PG_locked to operate on head page.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
 include/linux/page-flags.h | 3 ++-
 include/linux/pagemap.h    | 5 +++++
 mm/filemap.c               | 1 +
 mm/slub.c                  | 2 ++
 4 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index e1f5fcd79792..676f72d29ac2 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -203,7 +203,8 @@ static inline int __TestClearPage##uname(struct page *page) { return 0; }
 
 struct page;	/* forward declaration */
 
-TESTPAGEFLAG(Locked, locked)
+#define PageLocked(page) test_bit(PG_locked, &compound_head(page)->flags)
+
 PAGEFLAG(Error, error) TESTCLEARFLAG(Error, error)
 PAGEFLAG(Referenced, referenced) TESTCLEARFLAG(Referenced, referenced)
 	__SETPAGEFLAG(Referenced, referenced)
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 3df8c7db7a4e..110e86e480bb 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -445,16 +445,19 @@ extern void unlock_page(struct page *page);
 
 static inline void __set_page_locked(struct page *page)
 {
+	VM_BUG_ON_PAGE(PageTail(page), page);
 	__set_bit(PG_locked, &page->flags);
 }
 
 static inline void __clear_page_locked(struct page *page)
 {
+	VM_BUG_ON_PAGE(PageTail(page), page);
 	__clear_bit(PG_locked, &page->flags);
 }
 
 static inline int trylock_page(struct page *page)
 {
+	page = compound_head(page);
 	return (likely(!test_and_set_bit_lock(PG_locked, &page->flags)));
 }
 
@@ -505,6 +508,7 @@ extern int wait_on_page_bit_killable(struct page *page, int bit_nr);
 
 static inline int wait_on_page_locked_killable(struct page *page)
 {
+	page = compound_head(page);
 	if (PageLocked(page))
 		return wait_on_page_bit_killable(page, PG_locked);
 	return 0;
@@ -519,6 +523,7 @@ static inline int wait_on_page_locked_killable(struct page *page)
  */
 static inline void wait_on_page_locked(struct page *page)
 {
+	page = compound_head(page);
 	if (PageLocked(page))
 		wait_on_page_bit(page, PG_locked);
 }
diff --git a/mm/filemap.c b/mm/filemap.c
index f501b56ec2c6..020d4afd45df 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -735,6 +735,7 @@ EXPORT_SYMBOL_GPL(add_page_wait_queue);
  */
 void unlock_page(struct page *page)
 {
+	page = compound_head(page);
 	VM_BUG_ON_PAGE(!PageLocked(page), page);
 	clear_bit_unlock(PG_locked, &page->flags);
 	smp_mb__after_atomic();
diff --git a/mm/slub.c b/mm/slub.c
index 3e8afcc07a76..de37b20abaa9 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -347,11 +347,13 @@ static inline int oo_objects(struct kmem_cache_order_objects x)
  */
 static __always_inline void slab_lock(struct page *page)
 {
+	VM_BUG_ON_PAGE(PageTail(page), page);
 	bit_spin_lock(PG_locked, &page->flags);
 }
 
 static __always_inline void slab_unlock(struct page *page)
 {
+	VM_BUG_ON_PAGE(PageTail(page), page);
 	__bit_spin_unlock(PG_locked, &page->flags);
 }
 
-- 
2.1.1

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