mm: move page_mapping_file to pagemap.h

page_mapping_file() is only used by some architectures, and then it
is usually only used in one place.  Make it a static inline function
so other architectures don't have to carry this dead code.

Link: https://lkml.kernel.org/r/20210317123011.350118-1-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Acked-by: Mike Rapoport <rppt@linux.ibm.com>
Cc: Huang Ying <ying.huang@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/arm/mm/copypage-v4mc.c

@@ -13,6 +13,7 @@
 #include <linux/init.h>
 #include <linux/mm.h>
 #include <linux/highmem.h>
+#include <linux/pagemap.h>
 
 #include <asm/tlbflush.h>
 #include <asm/cacheflush.h>

arch/arm/mm/copypage-v6.c

@@ -8,6 +8,7 @@
 #include <linux/spinlock.h>
 #include <linux/mm.h>
 #include <linux/highmem.h>
+#include <linux/pagemap.h>
 
 #include <asm/shmparam.h>
 #include <asm/tlbflush.h>

arch/arm/mm/copypage-xscale.c

@@ -13,6 +13,7 @@
 #include <linux/init.h>
 #include <linux/mm.h>
 #include <linux/highmem.h>
+#include <linux/pagemap.h>
 
 #include <asm/tlbflush.h>
 #include <asm/cacheflush.h>

arch/csky/abiv1/cacheflush.c

@@ -4,6 +4,7 @@
 #include <linux/kernel.h>
 #include <linux/mm.h>
 #include <linux/fs.h>
+#include <linux/pagemap.h>
 #include <linux/syscalls.h>
 #include <linux/spinlock.h>
 #include <asm/page.h>

arch/mips/mm/cache.c

@@ -15,6 +15,7 @@
 #include <linux/syscalls.h>
 #include <linux/mm.h>
 #include <linux/highmem.h>
+#include <linux/pagemap.h>
 
 #include <asm/cacheflush.h>
 #include <asm/processor.h>

arch/nios2/mm/cacheflush.c

@@ -11,6 +11,7 @@
 #include <linux/sched.h>
 #include <linux/mm.h>
 #include <linux/fs.h>
+#include <linux/pagemap.h>
 
 #include <asm/cacheflush.h>
 #include <asm/cpuinfo.h>

arch/sh/mm/cache-sh4.c

@@ -16,6 +16,7 @@
 #include <linux/mutex.h>
 #include <linux/fs.h>
 #include <linux/highmem.h>
+#include <linux/pagemap.h>
 #include <asm/mmu_context.h>
 #include <asm/cache_insns.h>
 #include <asm/cacheflush.h>

arch/sh/mm/cache-sh7705.c

@@ -13,6 +13,7 @@
 #include <linux/mman.h>
 #include <linux/mm.h>
 #include <linux/fs.h>
+#include <linux/pagemap.h>
 #include <linux/threads.h>
 #include <asm/addrspace.h>
 #include <asm/page.h>

arch/sparc/mm/tlb.c

@@ -9,6 +9,7 @@
 #include <linux/mm.h>
 #include <linux/swap.h>
 #include <linux/preempt.h>
+#include <linux/pagemap.h>
 
 #include <asm/tlbflush.h>
 #include <asm/cacheflush.h>

include/linux/mm.h

@@ -1629,7 +1629,6 @@ static inline pgoff_t page_index(struct page *page)
 
 bool page_mapped(struct page *page);
 struct address_space *page_mapping(struct page *page);
-struct address_space *page_mapping_file(struct page *page);
 
 /*
  * Return true only if the page has been allocated with

include/linux/pagemap.h

@@ -157,6 +157,16 @@ static inline void filemap_nr_thps_dec(struct address_space *mapping)
 
 void release_pages(struct page **pages, int nr);
 
+/*
+ * For file cache pages, return the address_space, otherwise return NULL
+ */
+static inline struct address_space *page_mapping_file(struct page *page)
+{
+	if (unlikely(PageSwapCache(page)))
+		return NULL;
+	return page_mapping(page);
+}
+
 /*
  * speculatively take a reference to a page.
  * If the page is free (_refcount == 0), then _refcount is untouched, and 0

mm/util.c

@@ -711,16 +711,6 @@ struct address_space *page_mapping(struct page *page)
 }
 EXPORT_SYMBOL(page_mapping);
 
-/*
- * For file cache pages, return the address_space, otherwise return NULL
- */
-struct address_space *page_mapping_file(struct page *page)
-{
-	if (unlikely(PageSwapCache(page)))
-		return NULL;
-	return page_mapping(page);
-}
-
 /* Slow path of page_mapcount() for compound pages */
 int __page_mapcount(struct page *page)
 {