mm, page_alloc: pull out side effects from free_pages_check

Check without side-effects should be easier to maintain.  It also
removes the duplicated cpupid and flags reset done in !DEBUG_VM variant
of both free_pcp_prepare() and then bulkfree_pcp_prepare().  Finally, it
enables the next patch.

It shouldn't result in new branches, thanks to inlining of the check.

!DEBUG_VM bloat-o-meter:

  add/remove: 0/0 grow/shrink: 0/2 up/down: 0/-27 (-27)
  function                                     old     new   delta
  __free_pages_ok                              748     739      -9
  free_pcppages_bulk                          1403    1385     -18

DEBUG_VM:

  add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-28 (-28)
  function                                     old     new   delta
  free_pages_prepare                           806     778     -28

This is also slightly faster because cpupid information is not set on
tail pages so we can avoid resets there.

Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/page_alloc.c

@@ -833,11 +833,8 @@ static void free_pages_check_bad(struct page *page)
 
 static inline int free_pages_check(struct page *page)
 {
-	if (likely(page_expected_state(page, PAGE_FLAGS_CHECK_AT_FREE))) {
-		page_cpupid_reset_last(page);
-		page->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
+	if (likely(page_expected_state(page, PAGE_FLAGS_CHECK_AT_FREE)))
 		return 0;
-	}
 
 	/* Something has gone sideways, find it */
 	free_pages_check_bad(page);
@@ -1078,7 +1075,11 @@ static bool free_pages_prepare(struct page *page, unsigned int order)
 		for (i = 1; i < (1 << order); i++) {
 			if (compound)
 				bad += free_tail_pages_check(page, page + i);
-			bad += free_pages_check(page + i);
+			if (unlikely(free_pages_check(page + i))) {
+				bad++;
+				continue;
+			}
+			(page + i)->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
 		}
 	}
 	if (PageAnonHead(page))
@@ -1087,6 +1088,8 @@ static bool free_pages_prepare(struct page *page, unsigned int order)
 	if (bad)
 		return false;
 
+	page_cpupid_reset_last(page);
+	page->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
 	reset_page_owner(page, order);
 
 	if (!PageHighMem(page)) {