[PATCH v6 07/27] mm: Add get_folio

Matthew Wilcox (Oracle)
2021-03-31T18:50:51Z

If we know we have a folio, we can call get_folio() instead
of get_page() and save the overhead of calling compound_head().

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Zi Yan <ziy@nvidia.com>
---
include/linux/mm.h | 26 +++++++++++++++++---------
1 file changed, 17 insertions(+), 9 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 824acedc1253..818010a6b4c9 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1205,18 +1205,26 @@ static inline bool is_pci_p2pdma_page(const struct page *page)
}

/* 127: arbitrary random number, small enough to assemble well */
-#define page_ref_zero_or_close_to_overflow(page) \
- ((unsigned int) page_ref_count(page) + 127u <= 127u)
+#define folio_ref_zero_or_close_to_overflow(folio) \
+ ((unsigned int) folio_ref_count(folio) + 127u <= 127u)
+
+/**
+ * get_folio - Increment the reference count on a folio.
+ * @folio: The folio.
+ *
+ * Context: May be called in any context, as long as you know that
+ * you have a refcount on the folio. If you do not already have one,
+ * try_grab_page() may be the right interface for you to use.
+ */
+static inline void get_folio(struct folio *folio)
+{
+ VM_BUG_ON_FOLIO(folio_ref_zero_or_close_to_overflow(folio), folio);
+ folio_ref_inc(folio);
+}

static inline void get_page(struct page *page)
{
- page = compound_head(page);
- /*
- * Getting a normal page or the head of a compound page
- * requires to already have an elevated page->_refcount.
- */
- VM_BUG_ON_PAGE(page_ref_zero_or_close_to_overflow(page), page);
- page_ref_inc(page);
+ get_folio(page_folio(page));
}

bool __must_check try_grab_page(struct page *page, unsigned int flags);
--
2.30.2