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

On Mon, Jun 7, 2021 at 3:53 PM Matthew Wilcox [off-list ref] wrote:

On Sun, Jun 06, 2021 at 03:50:54AM +0200, Matteo Croce wrote:

quoted

And change all the *_pfmemalloc functions to use page->lru.next like this?

@@ -1668,10 +1668,12 @@ struct address_space *page_mapping(struct page *page);

static inline bool page_is_pfmemalloc(const struct page *page)
{
       /*
-        * Page index cannot be this large so this must be
-        * a pfmemalloc page.
+        * This is not a tail page; compound_head of a head page is unused
+        * at return from the page allocator, and will be overwritten
+        * by callers who do not care whether the page came from the
+        * reserves.
        */

The comment doesn't make a lot of sense if we're switching to use
lru.next.  How about:

        /*
         * lru.next has bit 1 set if the page is allocated from the
         * pfmemalloc reserves.  Callers may simply overwrite it if
         * they do not need to preserve that information.
         */

Sounds good!

-- 
per aspera ad upstream