diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 5543c1fb490124cabf70d5cbf8744aa136161350..4aad622ee305a6d3a2167eefa667c6521419ca18 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3198,6 +3198,29 @@ static inline bool should_fail_alloc_page(gfp_t gfp_mask, unsigned int order)
 
 #endif /* CONFIG_FAIL_PAGE_ALLOC */
 
+static inline long __zone_watermark_unusable_free(struct zone *z,
+				unsigned int order, unsigned int alloc_flags)
+{
+	const bool alloc_harder = (alloc_flags & (ALLOC_HARDER|ALLOC_OOM));
+	long unusable_free = (1 << order) - 1;
+
+	/*
+	 * If the caller does not have rights to ALLOC_HARDER then subtract
+	 * the high-atomic reserves. This will over-estimate the size of the
+	 * atomic reserve but it avoids a search.
+	 */
+	if (likely(!alloc_harder))
+		unusable_free += z->nr_reserved_highatomic;
+
+#ifdef CONFIG_CMA
+	/* If allocation can't use CMA areas don't use free CMA pages */
+	if (!(alloc_flags & ALLOC_CMA))
+		unusable_free += zone_page_state(z, NR_FREE_CMA_PAGES);
+#endif
+
+	return unusable_free;
+}
+
 /*
  * Return true if free base pages are above 'mark'. For high-order checks it
  * will return true of the order-0 watermark is reached and there is at least
@@ -3213,19 +3236,12 @@ bool __zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark,
 	const bool alloc_harder = (alloc_flags & (ALLOC_HARDER|ALLOC_OOM));
 
 	/* free_pages may go negative - that's OK */
-	free_pages -= (1 << order) - 1;
+	free_pages -= __zone_watermark_unusable_free(z, order, alloc_flags);
 
 	if (alloc_flags & ALLOC_HIGH)
 		min -= min / 2;
 
-	/*
-	 * If the caller does not have rights to ALLOC_HARDER then subtract
-	 * the high-atomic reserves. This will over-estimate the size of the
-	 * atomic reserve but it avoids a search.
-	 */
-	if (likely(!alloc_harder)) {
-		free_pages -= z->nr_reserved_highatomic;
-	} else {
+	if (unlikely(alloc_harder)) {
 		/*
 		 * OOM victims can try even harder than normal ALLOC_HARDER
 		 * users on the grounds that it's definitely going to be in
@@ -3238,13 +3254,6 @@ bool __zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark,
 			min -= min / 4;
 	}
 
-
-#ifdef CONFIG_CMA
-	/* If allocation can't use CMA areas don't use free CMA pages */
-	if (!(alloc_flags & ALLOC_CMA))
-		free_pages -= zone_page_state(z, NR_FREE_CMA_PAGES);
-#endif
-
 	/*
 	 * Check watermarks for an order-0 allocation request. If these
 	 * are not met, then a high-order request also cannot go ahead
@@ -3291,28 +3300,26 @@ bool zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark,
 }
 
 static inline bool zone_watermark_fast(struct zone *z, unsigned int order,
-		unsigned long mark, int classzone_idx, unsigned int alloc_flags)
+		unsigned long mark, int highest_zoneidx, unsigned int alloc_flags)
 {
-	long free_pages = zone_page_state(z, NR_FREE_PAGES);
-	long cma_pages = 0;
+	long free_pages;
 
-#ifdef CONFIG_CMA
-	/* If allocation can't use CMA areas don't use free CMA pages */
-	if (!(alloc_flags & ALLOC_CMA))
-		cma_pages = zone_page_state(z, NR_FREE_CMA_PAGES);
-#endif
+	free_pages = zone_page_state(z, NR_FREE_PAGES);
 
 	/*
 	 * Fast check for order-0 only. If this fails then the reserves
-	 * need to be calculated. There is a corner case where the check
-	 * passes but only the high-order atomic reserve are free. If
-	 * the caller is !atomic then it'll uselessly search the free
-	 * list. That corner case is then slower but it is harmless.
+	 * need to be calculated.
 	 */
-	if (!order && (free_pages - cma_pages) > mark + z->lowmem_reserve[classzone_idx])
-		return true;
+	if (!order) {
+		long fast_free;
 
-	return __zone_watermark_ok(z, order, mark, classzone_idx, alloc_flags,
+		fast_free = free_pages;
+		fast_free -= __zone_watermark_unusable_free(z, 0, alloc_flags);
+		if (fast_free > mark + z->lowmem_reserve[highest_zoneidx])
+			return true;
+	}
+
+	return __zone_watermark_ok(z, order, mark, highest_zoneidx, alloc_flags,
 					free_pages);
 }