Re: [PATCH net-next v7 1/5] mm: add a signature in struct page

[Matthew Wilcox]

On Fri, Jun 04, 2021 at 08:33:45PM +0200, Matteo Croce wrote:
> @@ -130,7 +137,10 @@ struct page {
>  			};
>  		};
>  		struct {	/* Tail pages of compound page */
> -			unsigned long compound_head;	/* Bit zero is set */
> +			/* Bit zero is set
> +			 * Bit one if pfmemalloc page
> +			 */
> +			unsigned long compound_head;

I would drop this hunk.  Bit 1 is not used for this purpose in tail
pages; it's used for that purpose in head and base pages.

I suppose we could do something like ...

 static inline void set_page_pfmemalloc(struct page *page)
 {
-	page->index = -1UL;
+	page->lru.next = (void *)2;
 }

if it's causing confusion.