khugepaged: rename collapse_shmem() and khugepaged_scan_shmem()

Next patch will add khugepaged support of non-shmem files.  This patch
renames these two functions to reflect the new functionality:

    collapse_shmem()        =>  collapse_file()
    khugepaged_scan_shmem() =>  khugepaged_scan_file()

Link: http://lkml.kernel.org/r/20190801184244.3169074-6-songliubraving@fb.comSigned-off-by: Song Liu <songliubraving@fb.com>
Acked-by: Rik van Riel <riel@surriel.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Hillf Danton <hdanton@sina.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: William Kucharski <william.kucharski@oracle.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/khugepaged.c

@@ -1287,7 +1287,7 @@ static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
 }
 
 /**
- * collapse_shmem - collapse small tmpfs/shmem pages into huge one.
+ * collapse_file - collapse small tmpfs/shmem pages into huge one.
  *
  * Basic scheme is simple, details are more complex:
  *  - allocate and lock a new huge page;
@@ -1304,10 +1304,11 @@ static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
  *    + restore gaps in the page cache;
  *    + unlock and free huge page;
  */
-static void collapse_shmem(struct mm_struct *mm,
-		struct address_space *mapping, pgoff_t start,
+static void collapse_file(struct mm_struct *mm,
+		struct file *file, pgoff_t start,
 		struct page **hpage, int node)
 {
+	struct address_space *mapping = file->f_mapping;
 	gfp_t gfp;
 	struct page *new_page;
 	struct mem_cgroup *memcg;
@@ -1563,11 +1564,11 @@ static void collapse_shmem(struct mm_struct *mm,
 	/* TODO: tracepoints */
 }
 
-static void khugepaged_scan_shmem(struct mm_struct *mm,
-		struct address_space *mapping,
-		pgoff_t start, struct page **hpage)
+static void khugepaged_scan_file(struct mm_struct *mm,
+		struct file *file, pgoff_t start, struct page **hpage)
 {
 	struct page *page = NULL;
+	struct address_space *mapping = file->f_mapping;
 	XA_STATE(xas, &mapping->i_pages, start);
 	int present, swap;
 	int node = NUMA_NO_NODE;
@@ -1631,16 +1632,15 @@ static void khugepaged_scan_shmem(struct mm_struct *mm,
 			result = SCAN_EXCEED_NONE_PTE;
 		} else {
 			node = khugepaged_find_target_node();
-			collapse_shmem(mm, mapping, start, hpage, node);
+			collapse_file(mm, file, start, hpage, node);
 		}
 	}
 
 	/* TODO: tracepoints */
 }
 #else
-static void khugepaged_scan_shmem(struct mm_struct *mm,
-		struct address_space *mapping,
-		pgoff_t start, struct page **hpage)
+static void khugepaged_scan_file(struct mm_struct *mm,
+		struct file *file, pgoff_t start, struct page **hpage)
 {
 	BUILD_BUG();
 }
@@ -1722,8 +1722,7 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
 				file = get_file(vma->vm_file);
 				up_read(&mm->mmap_sem);
 				ret = 1;
-				khugepaged_scan_shmem(mm, file->f_mapping,
-						pgoff, hpage);
+				khugepaged_scan_file(mm, file, pgoff, hpage);
 				fput(file);
 			} else {
 				ret = khugepaged_scan_pmd(mm, vma,