On Tue, Jan 04, 2022 at 12:01:45AM -0800, Christoph Hellwig wrote:
> On Sun, Jan 02, 2022 at 09:57:14PM +0000, Matthew Wilcox (Oracle) wrote:
> > -static inline bool hpage_pincount_available(struct page *page)
> > +static inline bool folio_pincount_available(struct folio *folio)
> > {
> > /*
> > - * Can the page->hpage_pinned_refcount field be used? That field is in
> > + * Can the folio->hpage_pinned_refcount field be used? That field is in
> > * the 3rd page of the compound page, so the smallest (2-page) compound
> > * pages cannot support it.
> > */
> > + return folio_order(folio) > 1;
> > +}
>
> Maybe convert the comment into a kerneldoc one?
I'm actually thinking about getting rid of it by moving the
hpage_pinned_refcount into page[1]:
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 4e763a590c9c..07fa8af564ed 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -950,7 +950,9 @@ static inline int head_compound_pincount(struct page *head)
static inline void set_compound_order(struct page *page, unsigned int order)
{
page[1].compound_order = order;
+#ifdef CONFIG_64BIT
page[1].compound_nr = 1U << order;
+#endif
}
/* Returns the number of pages in this potentially compound page. */
@@ -958,7 +960,11 @@ static inline unsigned long compound_nr(struct page *page)
{
if (!PageHead(page))
return 1;
+#ifdef CONFIG_64BIT
return page[1].compound_nr;
+#else
+ return 1UL << compound_order(page);
+#endif
}
/* Returns the number of bytes in this potentially compound page. */
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 09d9e2c4a2c5..e19af4a90a6c 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -150,11 +150,14 @@ struct page {
unsigned char compound_dtor;
unsigned char compound_order;
atomic_t compound_mapcount;
+ atomic_t hpage_pinned_refcount;
+#ifdef CONFIG_64BIT
unsigned int compound_nr; /* 1 << compound_order */
+#endif
};
struct { /* Second tail page of compound page */
unsigned long _compound_pad_1; /* compound_head */
- atomic_t hpage_pinned_refcount;
+ unsigned long _compound_pad_2;
/* For both global and memcg */
struct list_head deferred_list;
};
Now it's always available for every compound page.
