f2fs: no need to take page lock in readdir

VFS will take inode_lock for readdir, therefore no need to
take page lock in readdir at all just as the majority of
other generic filesystems.

This patch improves concurrency since .iterate_shared
was introduced to VFS years ago.
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/dir.c

@@ -896,7 +896,7 @@ static int f2fs_readdir(struct file *file, struct dir_context *ctx)
 			page_cache_sync_readahead(inode->i_mapping, ra, file, n,
 				min(npages - n, (pgoff_t)MAX_DIR_RA_PAGES));
 
-		dentry_page = f2fs_get_lock_data_page(inode, n, false);
+		dentry_page = f2fs_find_data_page(inode, n);
 		if (IS_ERR(dentry_page)) {
 			err = PTR_ERR(dentry_page);
 			if (err == -ENOENT) {
@@ -914,11 +914,11 @@ static int f2fs_readdir(struct file *file, struct dir_context *ctx)
 		err = f2fs_fill_dentries(ctx, &d,
 				n * NR_DENTRY_IN_BLOCK, &fstr);
 		if (err) {
-			f2fs_put_page(dentry_page, 1);
+			f2fs_put_page(dentry_page, 0);
 			break;
 		}
 
-		f2fs_put_page(dentry_page, 1);
+		f2fs_put_page(dentry_page, 0);
 	}
 out_free:
 	fscrypt_fname_free_buffer(&fstr);