mm: factor out common parts of write fault handling

Currently we duplicate handling of shared write faults in
wp_page_reuse() and do_shared_fault().  Factor them out into a common
function.

Link: http://lkml.kernel.org/r/1479460644-25076-12-git-send-email-jack@suse.cz
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memory.c

@@ -2062,6 +2062,41 @@ static int do_page_mkwrite(struct vm_area_struct *vma, struct page *page,
 	return ret;
 }
 
+/*
+ * Handle dirtying of a page in shared file mapping on a write fault.
+ *
+ * The function expects the page to be locked and unlocks it.
+ */
+static void fault_dirty_shared_page(struct vm_area_struct *vma,
+				    struct page *page)
+{
+	struct address_space *mapping;
+	bool dirtied;
+	bool page_mkwrite = vma->vm_ops && vma->vm_ops->page_mkwrite;
+
+	dirtied = set_page_dirty(page);
+	VM_BUG_ON_PAGE(PageAnon(page), page);
+	/*
+	 * Take a local copy of the address_space - page.mapping may be zeroed
+	 * by truncate after unlock_page().   The address_space itself remains
+	 * pinned by vma->vm_file's reference.  We rely on unlock_page()'s
+	 * release semantics to prevent the compiler from undoing this copying.
+	 */
+	mapping = page_rmapping(page);
+	unlock_page(page);
+
+	if ((dirtied || page_mkwrite) && mapping) {
+		/*
+		 * Some device drivers do not set page.mapping
+		 * but still dirty their pages
+		 */
+		balance_dirty_pages_ratelimited(mapping);
+	}
+
+	if (!page_mkwrite)
+		file_update_time(vma->vm_file);
+}
+
 /*
  * Handle write page faults for pages that can be reused in the current vma
  *
@@ -2092,28 +2127,11 @@ static inline int wp_page_reuse(struct vm_fault *vmf, struct page *page,
 	pte_unmap_unlock(vmf->pte, vmf->ptl);
 
 	if (dirty_shared) {
-		struct address_space *mapping;
-		int dirtied;
-
 		if (!page_mkwrite)
 			lock_page(page);
 
-		dirtied = set_page_dirty(page);
-		VM_BUG_ON_PAGE(PageAnon(page), page);
-		mapping = page->mapping;
-		unlock_page(page);
+		fault_dirty_shared_page(vma, page);
 		put_page(page);
-
-		if ((dirtied || page_mkwrite) && mapping) {
-			/*
-			 * Some device drivers do not set page.mapping
-			 * but still dirty their pages
-			 */
-			balance_dirty_pages_ratelimited(mapping);
-		}
-
-		if (!page_mkwrite)
-			file_update_time(vma->vm_file);
 	}
 
 	return VM_FAULT_WRITE;
@@ -3294,8 +3312,6 @@ uncharge_out:
 static int do_shared_fault(struct vm_fault *vmf)
 {
 	struct vm_area_struct *vma = vmf->vma;
-	struct address_space *mapping;
-	int dirtied = 0;
 	int ret, tmp;
 
 	ret = __do_fault(vmf);
@@ -3324,27 +3340,7 @@ static int do_shared_fault(struct vm_fault *vmf)
 		return ret;
 	}
 
-	if (set_page_dirty(vmf->page))
-		dirtied = 1;
-	/*
-	 * Take a local copy of the address_space - page.mapping may be zeroed
-	 * by truncate after unlock_page().   The address_space itself remains
-	 * pinned by vma->vm_file's reference.  We rely on unlock_page()'s
-	 * release semantics to prevent the compiler from undoing this copying.
-	 */
-	mapping = page_rmapping(vmf->page);
-	unlock_page(vmf->page);
-	if ((dirtied || vma->vm_ops->page_mkwrite) && mapping) {
-		/*
-		 * Some device drivers do not set page.mapping but still
-		 * dirty their pages
-		 */
-		balance_dirty_pages_ratelimited(mapping);
-	}
-
-	if (!vma->vm_ops->page_mkwrite)
-		file_update_time(vma->vm_file);
-
+	fault_dirty_shared_page(vma, vmf->page);
 	return ret;
 }