Use zero_user_page() in ext4 where possible

Signed-off-by: NEric Sandeen <sandeen@redhat.com>
Signed-off-by: N"Theodore Ts'o" <tytso@mit.edu>

fs/ext4/inode.c

@@ -1766,7 +1766,6 @@ int ext4_block_truncate_page(handle_t *handle, struct page *page,
 	struct inode *inode = mapping->host;
 	struct buffer_head *bh;
 	int err = 0;
-	void *kaddr;
 
 	blocksize = inode->i_sb->s_blocksize;
 	length = blocksize - (offset & (blocksize - 1));
@@ -1778,10 +1777,7 @@ int ext4_block_truncate_page(handle_t *handle, struct page *page,
 	 */
 	if (!page_has_buffers(page) && test_opt(inode->i_sb, NOBH) &&
 	     ext4_should_writeback_data(inode) && PageUptodate(page)) {
-		kaddr = kmap_atomic(page, KM_USER0);
-		memset(kaddr + offset, 0, length);
-		flush_dcache_page(page);
-		kunmap_atomic(kaddr, KM_USER0);
+		zero_user_page(page, offset, length, KM_USER0);
 		set_page_dirty(page);
 		goto unlock;
 	}
@@ -1834,10 +1830,7 @@ int ext4_block_truncate_page(handle_t *handle, struct page *page,
 			goto unlock;
 	}
 
-	kaddr = kmap_atomic(page, KM_USER0);
-	memset(kaddr + offset, 0, length);
-	flush_dcache_page(page);
-	kunmap_atomic(kaddr, KM_USER0);
+	zero_user_page(page, offset, length, KM_USER0);
 
 	BUFFER_TRACE(bh, "zeroed end of block");