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Date:   Wed, 16 Dec 2020 18:23:33 +0000
From:   "Matthew Wilcox (Oracle)" <>
Cc:     "Matthew Wilcox (Oracle)" <>,
Subject: [PATCH 23/25] mm: Add flush_dcache_folio

This is a default implementation which calls flush_dcache_page() on
each page in the folio.  If architectures can do better, they should
implement their own version of it.

Signed-off-by: Matthew Wilcox (Oracle) <>
 Documentation/core-api/cachetlb.rst |  6 ++++++
 include/asm-generic/cacheflush.h    | 13 +++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/Documentation/core-api/cachetlb.rst b/Documentation/core-api/cachetlb.rst
index a1582cc79f0f..484cf31fcded 100644
--- a/Documentation/core-api/cachetlb.rst
+++ b/Documentation/core-api/cachetlb.rst
@@ -325,6 +325,12 @@ maps this page at its virtual address.
 			dirty.  Again, see sparc64 for examples of how
 			to deal with this.
+  ``void flush_dcache_folio(struct folio *folio)``
+	This function is called under the same circumstances as
+	flush_dcache_page().  It allows the architecture to
+	optimise for flushing the entire folio of pages instead
+	of flushing one page at a time.
   ``void copy_to_user_page(struct vm_area_struct *vma, struct page *page,
   unsigned long user_vaddr, void *dst, void *src, int len)``
   ``void copy_from_user_page(struct vm_area_struct *vma, struct page *page,
diff --git a/include/asm-generic/cacheflush.h b/include/asm-generic/cacheflush.h
index 4a674db4e1fa..5537ea24333d 100644
--- a/include/asm-generic/cacheflush.h
+++ b/include/asm-generic/cacheflush.h
@@ -49,9 +49,22 @@ static inline void flush_cache_page(struct vm_area_struct *vma,
 static inline void flush_dcache_page(struct page *page)
+static inline void flush_dcache_folio(struct folio *folio) { }
+static inline void flush_dcache_folio(struct folio *folio)
+	unsigned int n = folio_nr_pages(folio);
+	do {
+		flush_dcache_page(&folio->page[--n]);
+	} while (n);
 #ifndef flush_dcache_mmap_lock
 static inline void flush_dcache_mmap_lock(struct address_space *mapping)

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