ext4: support large block size in ext4_mb_get_buddy_page_lock()

ext4: support large block size in ext4_mb_get_buddy_page_lock()

Currently, ext4_mb_get_buddy_page_lock() uses blocks_per_page to calculate
folio index and offset. However, when blocksize is larger than PAGE_SIZE,
blocks_per_page becomes zero, leading to a potential division-by-zero bug.

To support BS > PS, use bytes to compute folio index and offset within
folio to get rid of blocks_per_page.

Also, since ext4_mb_get_buddy_page_lock() already fully supports folio,
rename it to ext4_mb_get_buddy_folio_lock().

Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Message-ID: <20251121090654.631996-13-libaokun@huaweicloud.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>