[PATCH] fewer unlikely tests

[Hugh Dickins]

Occasionally I worry about all those BUG_ON tests we keep adding into
page_alloc.c.  This patch does one preliminary test of all the flags
before trying individually.  Maybe you consider this in bad taste,
or maybe you think it's worthwhile: as you wish.

--- 2.5.42-mm3/mm/page_alloc.c	Tue Oct 15 06:43:41 2002
+++ linux/mm/page_alloc.c	Tue Oct 15 13:14:35 2002
@@ -125,12 +125,19 @@
 
 static void free_pages_check(struct page *page)
 {
-	BUG_ON(PageLRU(page));
-	BUG_ON(PagePrivate(page));
-	BUG_ON(page->mapping != NULL);
-	BUG_ON(PageLocked(page));
-	BUG_ON(PageActive(page));
-	BUG_ON(PageWriteback(page));
+	BUG_ON(page->mapping);
+	if (unlikely(page->flags & (
+		1 << PG_lru	|
+		1 << PG_private |
+		1 << PG_locked	|
+		1 << PG_active	|
+		1 << PG_writeback ))) {
+		BUG_ON(PageLRU(page));
+		BUG_ON(PagePrivate(page));
+		BUG_ON(PageLocked(page));
+		BUG_ON(PageActive(page));
+		BUG_ON(PageWriteback(page));
+	}
 	BUG_ON(page->pte.direct != 0);
 	if (PageDirty(page))
 		ClearPageDirty(page);
@@ -204,12 +211,20 @@
 static struct page *prep_new_page(struct page *page)
 {
 	BUG_ON(page->mapping);
-	BUG_ON(PagePrivate(page));
-	BUG_ON(PageLocked(page));
-	BUG_ON(PageLRU(page));
-	BUG_ON(PageActive(page));
-	BUG_ON(PageDirty(page));
-	BUG_ON(PageWriteback(page));
+	if (unlikely(page->flags & (
+		1 << PG_private	|
+		1 << PG_locked	|
+		1 << PG_lru	|
+		1 << PG_active	|
+		1 << PG_dirty	|
+		1 << PG_writeback ))) {
+		BUG_ON(PagePrivate(page));
+		BUG_ON(PageLocked(page));
+		BUG_ON(PageLRU(page));
+		BUG_ON(PageActive(page));
+		BUG_ON(PageDirty(page));
+		BUG_ON(PageWriteback(page));
+	}
 	BUG_ON(page->pte.direct != 0);
 	page->flags &= ~(1 << PG_uptodate | 1 << PG_error |
 			1 << PG_referenced | 1 << PG_arch_1 |