mm/page_alloc: add a missing mm_page_alloc_zone_locked() tracepoint

The trace point *trace_mm_page_alloc_zone_locked()* in __rmqueue() does
not currently cover all branches.  Add the missing tracepoint and check
the page before do that.

[akpm@linux-foundation.org: use IS_ENABLED() to suppress warning]

Link: https://lkml.kernel.org/r/20201228132901.41523-1-carver4lio@163.com
Signed-off-by: Hailong liu <liu.hailong6@zte.com.cn>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/page_alloc.c

@@ -2862,20 +2862,20 @@ __rmqueue(struct zone *zone, unsigned int order, int migratetype,
 {
 	struct page *page;
 
-#ifdef CONFIG_CMA
-	/*
-	 * Balance movable allocations between regular and CMA areas by
-	 * allocating from CMA when over half of the zone's free memory
-	 * is in the CMA area.
-	 */
-	if (alloc_flags & ALLOC_CMA &&
-	    zone_page_state(zone, NR_FREE_CMA_PAGES) >
-	    zone_page_state(zone, NR_FREE_PAGES) / 2) {
-		page = __rmqueue_cma_fallback(zone, order);
-		if (page)
-			return page;
+	if (IS_ENABLED(CONFIG_CMA)) {
+		/*
+		 * Balance movable allocations between regular and CMA areas by
+		 * allocating from CMA when over half of the zone's free memory
+		 * is in the CMA area.
+		 */
+		if (alloc_flags & ALLOC_CMA &&
+		    zone_page_state(zone, NR_FREE_CMA_PAGES) >
+		    zone_page_state(zone, NR_FREE_PAGES) / 2) {
+			page = __rmqueue_cma_fallback(zone, order);
+			if (page)
+				goto out;
+		}
 	}
-#endif
 retry:
 	page = __rmqueue_smallest(zone, order, migratetype);
 	if (unlikely(!page)) {
@@ -2886,8 +2886,9 @@ retry:
 								alloc_flags))
 			goto retry;
 	}
-
-	trace_mm_page_alloc_zone_locked(page, order, migratetype);
+out:
+	if (page)
+		trace_mm_page_alloc_zone_locked(page, order, migratetype);
 	return page;
 }