linux-kernel - [PATCH v2 06/27] mm: Add get

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Date:   Mon, 18 Jan 2021 17:01:27 +0000
From:   "Matthew Wilcox (Oracle)" <willy@...radead.org>
To:     linux-fsdevel@...r.kernel.org, linux-mm@...ck.org
Cc:     "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2 06/27] mm: Add get_folio

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@...radead.org>
---
 include/linux/mm.h | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 4d135b62a2b6..380328930d6c 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1192,18 +1192,19 @@ 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) page_ref_count(&folio->page) + 127u <= 127u)
+
+static inline void get_folio(struct folio *folio)
+{
+	/* Getting a page requires an already elevated page->_refcount. */
+	VM_BUG_ON_FOLIO(folio_ref_zero_or_close_to_overflow(folio), folio);
+	page_ref_inc(&folio->page);
+}
 
 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);
-- 
2.29.2