On Fri, Jun 4, 2021 at 9:08 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
>
> 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.
>
If you prefer, ok for me.
Why not "(void *)BIT(1)"? Just to remark that it's a single bit and
not a magic like value?
--
per aspera ad upstream
