f2fs: reorganize f2fs_vm_page_mkwrite

Few things can be changed in the default mkwrite function
1) Make file_update_time at the start before acquiring any lock
2) the condition page_offset(page) >= i_size_read(inode) should be
 changed to page_offset(page) > i_size_read
3) Move wait_on_page_writeback.

Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Amit Sahrawat <a.sahrawat@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

fs/f2fs/file.c

@@ -63,9 +63,10 @@ static int f2fs_vm_page_mkwrite(struct vm_area_struct *vma,
 	f2fs_put_dnode(&dn);
 	mutex_unlock_op(sbi, ilock);
 
+	file_update_time(vma->vm_file);
 	lock_page(page);
 	if (page->mapping != inode->i_mapping ||
-			page_offset(page) >= i_size_read(inode) ||
+			page_offset(page) > i_size_read(inode) ||
 			!PageUptodate(page)) {
 		unlock_page(page);
 		err = -EFAULT;
@@ -76,10 +77,7 @@ static int f2fs_vm_page_mkwrite(struct vm_area_struct *vma,
 	 * check to see if the page is mapped already (no holes)
 	 */
 	if (PageMappedToDisk(page))
-		goto out;
-
-	/* fill the page */
-	wait_on_page_writeback(page);
+		goto mapped;
 
 	/* page is wholly or partially inside EOF */
 	if (((page->index + 1) << PAGE_CACHE_SHIFT) > i_size_read(inode)) {
@@ -90,7 +88,9 @@ static int f2fs_vm_page_mkwrite(struct vm_area_struct *vma,
 	set_page_dirty(page);
 	SetPageUptodate(page);
 
-	file_update_time(vma->vm_file);
+mapped:
+	/* fill the page */
+	wait_on_page_writeback(page);
 out:
 	sb_end_pagefault(inode->i_sb);
 	return block_page_mkwrite_return(err);