mm: uninline page_xchg_last_nid()

Andrew Morton pointed out that page_xchg_last_nid() and
reset_page_last_nid() were "getting nuttily large" and asked that it be
investigated.

reset_page_last_nid() is on the page free path and it would be
unfortunate to make that path more expensive than it needs to be.  Due
to the internal use of page_xchg_last_nid() it is already too expensive
but fortunately, it should also be impossible for the page->flags to be
updated in parallel when we call reset_page_last_nid().  Instead of
unlining the function, it uses a simplier implementation that assumes no
parallel updates and should now be sufficiently short for inlining.

page_xchg_last_nid() is called in paths that are already quite expensive
(splitting huge page, fault handling, migration) and it is reasonable to
uninline.  There was not really a good place to place the function but
mm/mmzone.c was the closest fit IMO.

This patch saved 128 bytes of text in the vmlinux file for the kernel
configuration I used for testing automatic NUMA balancing.
Signed-off-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/mm.h

@@ -677,25 +677,14 @@ static inline int page_last_nid(struct page *page)
 	return (page->flags >> LAST_NID_PGSHIFT) & LAST_NID_MASK;
 }
 
-static inline int page_xchg_last_nid(struct page *page, int nid)
-{
-	unsigned long old_flags, flags;
-	int last_nid;
-
-	do {
-		old_flags = flags = page->flags;
-		last_nid = page_last_nid(page);
-
-		flags &= ~(LAST_NID_MASK << LAST_NID_PGSHIFT);
-		flags |= (nid & LAST_NID_MASK) << LAST_NID_PGSHIFT;
-	} while (unlikely(cmpxchg(&page->flags, old_flags, flags) != old_flags));
-
-	return last_nid;
-}
+extern int page_xchg_last_nid(struct page *page, int nid);
 
 static inline void reset_page_last_nid(struct page *page)
 {
-	page_xchg_last_nid(page, (1 << LAST_NID_SHIFT) - 1);
+	int nid = (1 << LAST_NID_SHIFT) - 1;
+
+	page->flags &= ~(LAST_NID_MASK << LAST_NID_PGSHIFT);
+	page->flags |= (nid & LAST_NID_MASK) << LAST_NID_PGSHIFT;
 }
 #endif /* LAST_NID_NOT_IN_PAGE_FLAGS */
 #else

mm/mmzone.c

 /*
  * linux/mm/mmzone.c
  *
- * management codes for pgdats and zones.
+ * management codes for pgdats, zones and page flags
  */
 
 
@@ -96,3 +96,21 @@ void lruvec_init(struct lruvec *lruvec)
 	for_each_lru(lru)
 		INIT_LIST_HEAD(&lruvec->lists[lru]);
 }
+
+#if defined(CONFIG_NUMA_BALANCING) && !defined(LAST_NID_NOT_IN_PAGE_FLAGS)
+int page_xchg_last_nid(struct page *page, int nid)
+{
+	unsigned long old_flags, flags;
+	int last_nid;
+
+	do {
+		old_flags = flags = page->flags;
+		last_nid = page_last_nid(page);
+
+		flags &= ~(LAST_NID_MASK << LAST_NID_PGSHIFT);
+		flags |= (nid & LAST_NID_MASK) << LAST_NID_PGSHIFT;
+	} while (unlikely(cmpxchg(&page->flags, old_flags, flags) != old_flags));
+
+	return last_nid;
+}
+#endif