ext4: reduce unnecessary memory allocation in alloc_flex_gd()

ext4: reduce unnecessary memory allocation in alloc_flex_gd()

When a large flex_bg file system is resized, the number of groups to be
added may be small, and a large amount of memory that will not be used will
be allocated. Therefore, resize_bg can be set to the size after the number
of new_group_data to be used is aligned upwards to the power of 2. This
does not affect the disk layout after online resize and saves some memory.

Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20231023013057.2117948-5-libaokun1@huawei.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>