linux-kernel - [PATCH v7 08/28] mm: Add get

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Date:   Fri,  9 Apr 2021 19:50:45 +0100
From:   "Matthew Wilcox (Oracle)" <willy@...radead.org>
To:     linux-mm@...ck.org
Cc:     "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-cachefs@...hat.com, linux-afs@...ts.infradead.org,
        Zi Yan <ziy@...dia.com>, Christoph Hellwig <hch@....de>,
        Jeff Layton <jlayton@...nel.org>
Subject: [PATCH v7 08/28] 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>
Reviewed-by: Zi Yan <ziy@...dia.com>
Reviewed-by: Christoph Hellwig <hch@....de>
Acked-by: Jeff Layton <jlayton@...nel.org>
---
 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 747c6f47aef6..67d9104c1cc1 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1219,18 +1219,26 @@ 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