Different writeback timing since v5.14

[Richard Weinberger]

Hi!

Rafał and I discovered that page writeback on UBIFS behaves different since v5.14.
When a simple write, such as "echo foo > /mnt/ubibfs/bar.txt", happens it takes
a few seconds until writeback calls ubifs_writepage().

Before commit ab19939a6a50 ("mm/page-writeback: Fix performance when BDI's share of ratio is 0.")
it was 30 seconds (vm.dirty_expire_centisecs), after this change it happens after 5 seconds
(vm.dirty_writeback_centisecs).

Is this expected?
Just want to make sure that the said commit didn't uncover an UBIFS issue.

Thanks,
//richard