ext4: limit the maximum folio order

In environments with a page size of 64KB, the maximum size of a folio
can reach up to 128MB. Consequently, during the write-back of folios,
the 'rsv_blocks' will be overestimated to 1,577, which can make
pressure on the journal space where the journal is small. This can
easily exceed the limit of a single transaction. Besides, an excessively
large folio is meaningless and will instead increase the overhead of
traversing the bhs within the folio. Therefore, limit the maximum order
of a folio to 2048 filesystem blocks.

Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Reported-by: Joseph Qi <jiangqi903@gmail.com>
Closes: https://lore.kernel.org/linux-ext4/CA+G9fYsyYQ3ZL4xaSg1-Tt5Evto7Zd+hgNWZEa9cQLbahA1+xg@mail.gmail.com/


Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Tested-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/20250707140814.542883-12-yi.zhang@huaweicloud.com


Signed-off-by: Theodore Ts'o <tytso@mit.edu>