mm: introduce PAGEFLAGS_MASK to replace ((1UL << NR_PAGEFLAGS) - 1)

Instead of hard-coding ((1UL << NR_PAGEFLAGS) - 1) everywhere, introducing
PAGEFLAGS_MASK to make the code clear to get the page flags.

Link: https://lkml.kernel.org/r/20210819150712.59948-1-songmuchun@bytedance.com
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Roman Gushchin <guro@fb.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/page-flags.h

@@ -178,6 +178,8 @@ enum pageflags {
 	PG_reported = PG_uptodate,
 };
 
+#define PAGEFLAGS_MASK		((1UL << NR_PAGEFLAGS) - 1)
+
 #ifndef __GENERATING_BOUNDS_H
 
 static inline unsigned long _compound_head(const struct page *page)
@@ -859,7 +861,7 @@ static inline void ClearPageSlabPfmemalloc(struct page *page)
  * alloc-free cycle to prevent from reusing the page.
  */
 #define PAGE_FLAGS_CHECK_AT_PREP	\
-	(((1UL << NR_PAGEFLAGS) - 1) & ~__PG_HWPOISON)
+	(PAGEFLAGS_MASK & ~__PG_HWPOISON)
 
 #define PAGE_FLAGS_PRIVATE				\
 	(1UL << PG_private | 1UL << PG_private_2)

include/trace/events/page_ref.h

@@ -38,7 +38,7 @@ DECLARE_EVENT_CLASS(page_ref_mod_template,
 
 	TP_printk("pfn=0x%lx flags=%s count=%d mapcount=%d mapping=%p mt=%d val=%d",
 		__entry->pfn,
-		show_page_flags(__entry->flags & ((1UL << NR_PAGEFLAGS) - 1)),
+		show_page_flags(__entry->flags & PAGEFLAGS_MASK),
 		__entry->count,
 		__entry->mapcount, __entry->mapping, __entry->mt,
 		__entry->val)
@@ -88,7 +88,7 @@ DECLARE_EVENT_CLASS(page_ref_mod_and_test_template,
 
 	TP_printk("pfn=0x%lx flags=%s count=%d mapcount=%d mapping=%p mt=%d val=%d ret=%d",
 		__entry->pfn,
-		show_page_flags(__entry->flags & ((1UL << NR_PAGEFLAGS) - 1)),
+		show_page_flags(__entry->flags & PAGEFLAGS_MASK),
 		__entry->count,
 		__entry->mapcount, __entry->mapping, __entry->mt,
 		__entry->val, __entry->ret)

lib/test_printf.c

@@ -614,7 +614,7 @@ page_flags_test(int section, int node, int zone, int last_cpupid,
 	bool append = false;
 	int i;
 
-	flags &= BIT(NR_PAGEFLAGS) - 1;
+	flags &= PAGEFLAGS_MASK;
 	if (flags) {
 		page_flags |= flags;
 		snprintf(cmp_buf + size, BUF_SIZE - size, "%s", name);

lib/vsprintf.c

@@ -2019,7 +2019,7 @@ static const struct page_flags_fields pff[] = {
 static
 char *format_page_flags(char *buf, char *end, unsigned long flags)
 {
-	unsigned long main_flags = flags & (BIT(NR_PAGEFLAGS) - 1);
+	unsigned long main_flags = flags & PAGEFLAGS_MASK;
 	bool append = false;
 	int i;