mm: remove PageWaiters, PageSetWaiters and PageClearWaiters

All callers have been converted to use folios.  This was the only user of
PF_ONLY_HEAD, so remove that too.

Link: https://lkml.kernel.org/r/20240227192337.757313-3-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: Matthew Wilcox (Oracle)

include/linux/page-flags.h

@@ -328,9 +328,6 @@ static unsigned long *folio_flags(struct folio *folio, unsigned n)
  *     for compound page all operations related to the page flag applied to
  *     head page.
  *
- * PF_ONLY_HEAD:
- *     for compound page, callers only ever operate on the head page.
- *
  * PF_NO_TAIL:
  *     modifications of the page flag must be done on small or head pages,
  *     checks can be done on tail pages too.
@@ -346,9 +343,6 @@ static unsigned long *folio_flags(struct folio *folio, unsigned n)
 		page; })
 #define PF_ANY(page, enforce)	PF_POISONED_CHECK(page)
 #define PF_HEAD(page, enforce)	PF_POISONED_CHECK(compound_head(page))
-#define PF_ONLY_HEAD(page, enforce) ({					\
-		VM_BUG_ON_PGFLAGS(PageTail(page), page);		\
-		PF_POISONED_CHECK(page); })
 #define PF_NO_TAIL(page, enforce) ({					\
 		VM_BUG_ON_PGFLAGS(enforce && PageTail(page), page);	\
 		PF_POISONED_CHECK(compound_head(page)); })
@@ -362,7 +356,6 @@ static unsigned long *folio_flags(struct folio *folio, unsigned n)
 /* Which page is the flag stored in */
 #define FOLIO_PF_ANY		0
 #define FOLIO_PF_HEAD		0
-#define FOLIO_PF_ONLY_HEAD	0
 #define FOLIO_PF_NO_TAIL	0
 #define FOLIO_PF_NO_COMPOUND	0
 #define FOLIO_PF_SECOND		1
@@ -488,7 +481,7 @@ static inline int TestClearPage##uname(struct page *page) { return 0; }
 	TESTSETFLAG_FALSE(uname, lname) TESTCLEARFLAG_FALSE(uname, lname)
 
 __PAGEFLAG(Locked, locked, PF_NO_TAIL)
-PAGEFLAG(Waiters, waiters, PF_ONLY_HEAD)
+FOLIO_FLAG(waiters, FOLIO_HEAD_PAGE)
 PAGEFLAG(Error, error, PF_NO_TAIL) TESTCLEARFLAG(Error, error, PF_NO_TAIL)
 PAGEFLAG(Referenced, referenced, PF_HEAD)
 	TESTCLEARFLAG(Referenced, referenced, PF_HEAD)
@@ -1138,7 +1131,6 @@ static inline bool folio_has_private(struct folio *folio)
 
 #undef PF_ANY
 #undef PF_HEAD
-#undef PF_ONLY_HEAD
 #undef PF_NO_TAIL
 #undef PF_NO_COMPOUND
 #undef PF_SECOND