On Sun, Jul 05, 2020 at 12:45:41PM +0800, Coly Li wrote:

While I am thinking about this, I do appreciate your help about the
input on which configuration item should be stored in the on-disk
superblock.

Hi,

my use case is rather limited, all my bcache devices run in writeback
mode, and the only parameters I keep playing with are writeback_percent
and sequential_cutoff.

My short list of favourites:

   - cache_mode
   - writeback_percent
   - sequential_cutoff

But I vaguely remember that I used rebooting as last resort after too
much fiddling with tunables; persisting them in the superblock means
losing this reset-to-defaults method. Would be nice to have some other
way of resetting.

An alternative to modifying the superblock might be something
more out-of-band like iptables does with iptables-save and
iptables-restore: convert current settings to text, e.g. on shutdown or
at regular intervals, and restore settings on boot from this text file.

Regards
Matthias