mm: make page pfmemalloc check more robust

index 982fdcdc795b..b5b2925103ec 100644
@@ -216,7 +216,7 @@ static void fm10k_reuse_rx_page(struct fm10k_ring *rx_ring,
 
 static inline bool fm10k_page_is_reserved(struct page *page)
 {
-	return (page_to_nid(page) != numa_mem_id()) || page->pfmemalloc;
+	return (page_to_nid(page) != numa_mem_id()) || page_is_pfmemalloc(page);
 }
 
 static bool fm10k_can_reuse_rx_page(struct fm10k_rx_buffer *rx_buffer,

index 2f70a9b152bd..830466c49987 100644
@@ -6566,7 +6566,7 @@ static void igb_reuse_rx_page(struct igb_ring *rx_ring,
 
 static inline bool igb_page_is_reserved(struct page *page)
 {
-	return (page_to_nid(page) != numa_mem_id()) || page->pfmemalloc;
+	return (page_to_nid(page) != numa_mem_id()) || page_is_pfmemalloc(page);
 }
 
 static bool igb_can_reuse_rx_page(struct igb_rx_buffer *rx_buffer,

index 9aa6104e34ea..ae21e0b06c3a 100644
@@ -1832,7 +1832,7 @@ static void ixgbe_reuse_rx_page(struct ixgbe_ring *rx_ring,
 
 static inline bool ixgbe_page_is_reserved(struct page *page)
 {
-	return (page_to_nid(page) != numa_mem_id()) || page->pfmemalloc;
+	return (page_to_nid(page) != numa_mem_id()) || page_is_pfmemalloc(page);
 }
 
 /**

index e71cdde9cb01..1d7b00b038a2 100644
@@ -765,7 +765,7 @@ static void ixgbevf_reuse_rx_page(struct ixgbevf_ring *rx_ring,
 
 static inline bool ixgbevf_page_is_reserved(struct page *page)
 {
-	return (page_to_nid(page) != numa_mem_id()) || page->pfmemalloc;
+	return (page_to_nid(page) != numa_mem_id()) || page_is_pfmemalloc(page);
 }
 
 /**

index 2e872f92dbac..bf6f117fcf4d 100644
@@ -1003,6 +1003,34 @@ static inline int page_mapped(struct page *page)
 }
 
 /*
+ * Return true only if the page has been allocated with
+ * ALLOC_NO_WATERMARKS and the low watermark was not
+ * met implying that the system is under some pressure.
+ */
+static inline bool page_is_pfmemalloc(struct page *page)
+{
+	/*
+	 * Page index cannot be this large so this must be
+	 * a pfmemalloc page.
+	 */
+	return page->index == -1UL;
+}
+
+/*
+ * Only to be called by the page allocator on a freshly allocated
+ * page.
+ */
+static inline void set_page_pfmemalloc(struct page *page)
+{
+	page->index = -1UL;
+}
+
+static inline void clear_page_pfmemalloc(struct page *page)
+{
+	page->index = 0;
+}
+
+/*
  * Different kinds of faults, as returned by handle_mm_fault().
  * Used to decide whether a process gets delivered SIGBUS or
  * just gets major/minor fault counters bumped up.

index 0038ac7466fd..15549578d559 100644
@@ -63,15 +63,6 @@ struct page {
 		union {
 			pgoff_t index;		/* Our offset within mapping. */
 			void *freelist;		/* sl[aou]b first free object */
-			bool pfmemalloc;	/* If set by the page allocator,
-						 * ALLOC_NO_WATERMARKS was set
-						 * and the low watermark was not
-						 * met implying that the system
-						 * is under some pressure. The
-						 * caller should try ensure
-						 * this page is only used to
-						 * free other pages.
-						 */
 		};
 
 		union {

index d6cdd6e87d53..6dcee34a476f 100644
@@ -1602,20 +1602,16 @@ static inline void __skb_fill_page_desc(struct sk_buff *skb, int i,
 	skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
 
 	/*
-	 * Propagate page->pfmemalloc to the skb if we can. The problem is
-	 * that not all callers have unique ownership of the page. If
-	 * pfmemalloc is set, we check the mapping as a mapping implies
-	 * page->index is set (index and pfmemalloc share space).
-	 * If it's a valid mapping, we cannot use page->pfmemalloc but we
-	 * do not lose pfmemalloc information as the pages would not be
-	 * allocated using __GFP_MEMALLOC.
+	 * Propagate page pfmemalloc to the skb if we can. The problem is
+	 * that not all callers have unique ownership of the page but rely
+	 * on page_is_pfmemalloc doing the right thing(tm).
 	 */
 	frag->page.p		  = page;
 	frag->page_offset	  = off;
 	skb_frag_size_set(frag, size);
 
 	page = compound_head(page);
-	if (page->pfmemalloc && !page->mapping)
+	if (page_is_pfmemalloc(page))
 		skb->pfmemalloc	= true;
 }
 

@@ -2263,7 +2259,7 @@ static inline struct page *dev_alloc_page(void)
 static inline void skb_propagate_pfmemalloc(struct page *page,
 					     struct sk_buff *skb)
 {
-	if (page && page->pfmemalloc)
+	if (page_is_pfmemalloc(page))
 		skb->pfmemalloc = true;
 }
 

index beda41710802..a0e65dc89784 100644
@@ -1343,12 +1343,15 @@ static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
 	set_page_owner(page, order, gfp_flags);
 
 	/*
-	 * page->pfmemalloc is set when ALLOC_NO_WATERMARKS was necessary to
+	 * page is set pfmemalloc when ALLOC_NO_WATERMARKS was necessary to
 	 * allocate the page. The expectation is that the caller is taking
 	 * steps that will free more memory. The caller should avoid the page
 	 * being used for !PFMEMALLOC purposes.
 	 */
-	page->pfmemalloc = !!(alloc_flags & ALLOC_NO_WATERMARKS);
+	if (alloc_flags & ALLOC_NO_WATERMARKS)
+		set_page_pfmemalloc(page);
+	else
+		clear_page_pfmemalloc(page);
 
 	return 0;
 }

@@ -3345,7 +3348,7 @@ void *__alloc_page_frag(struct page_frag_cache *nc,
 		atomic_add(size - 1, &page->_count);
 
 		/* reset page count bias and offset to start of new frag */
-		nc->pfmemalloc = page->pfmemalloc;
+		nc->pfmemalloc = page_is_pfmemalloc(page);
 		nc->pagecnt_bias = size;
 		nc->offset = size;
 	}

index 200e22412a16..bbd0b47dc6a9 100644
@@ -1603,7 +1603,7 @@ static struct page *kmem_getpages(struct kmem_cache *cachep, gfp_t flags,
 	}
 
 	/* Record if ALLOC_NO_WATERMARKS was set when allocating the slab */
-	if (unlikely(page->pfmemalloc))
+	if (page_is_pfmemalloc(page))
 		pfmemalloc_active = true;
 
 	nr_pages = (1 << cachep->gfporder);

@@ -1614,7 +1614,7 @@ static struct page *kmem_getpages(struct kmem_cache *cachep, gfp_t flags,
 		add_zone_page_state(page_zone(page),
 			NR_SLAB_UNRECLAIMABLE, nr_pages);
 	__SetPageSlab(page);
-	if (page->pfmemalloc)
+	if (page_is_pfmemalloc(page))
 		SetPageSlabPfmemalloc(page);
 
 	if (kmemcheck_enabled && !(cachep->flags & SLAB_NOTRACK)) {

index 816df0016555..0eacabff35ab 100644
@@ -1427,7 +1427,7 @@ static struct page *new_slab(struct kmem_cache *s, gfp_t flags, int node)
 	inc_slabs_node(s, page_to_nid(page), page->objects);
 	page->slab_cache = s;
 	__SetPageSlab(page);
-	if (page->pfmemalloc)
+	if (page_is_pfmemalloc)
 		SetPageSlabPfmemalloc(page);
 
 	start = page_address(page);

index b6a19ca0f99e..6bb3d82c9bbe 100644
@@ -340,7 +340,7 @@ struct sk_buff *build_skb(void *data, unsigned int frag_size)
 
 	if (skb && frag_size) {
 		skb->head_frag = 1;
-		if (virt_to_head_page(data)->pfmemalloc)
+		if (page_is_pfmemalloc(virt_to_head_page(data)))
 			skb->pfmemalloc = 1;
 	}
 	return skb;