Things not done because probably disruptive:
* kmod filesystem string
* sysctl/debugfs/trace
* metrics names
* xmon instance names
Some of these might be renamed too, but starting with a relatively
safe set.
Also, split the timeouts for dentries and for stats. We generally
don't care if stats are out of dates, but dentries should be up
to date.
The code leaves various aspects to be desired:
* No attempt is made to only send stats when needed -- it is always
done. It might be a good idea to instead wait for the first two
stats to come back.
* Theres quite a bit of code duplication.
* It's pretty wasteful to have so many different packets for the
stats. It'd be much better to pack multiple requests and multiple
responses in single packets.
This could be done simply by allowing many requests to come
in the same packet (just one after the other would be fine),
and same for the responses. We can still use the protocol and
request id to keep track of things anyway.
I'm disabling prefetching since it doesn't make much of a difference
rightn now and it also seems to not do the right thing sometimes. I
don't want to fully investigate at this moment.
And hopefully reduce the likelihood of bugs. On the write end, given
that we do things less asynchronously, things might be a bit slower,
but I think the simplification is worth it for now.
Also, fix/improve a bunch of other stuff.
Initial version really by Pawel, but many changes in between.
Big outstanding issues:
* span cache reclamation (unbounded memory otherwise...)
* bad block service detection and workarounds
* corrupted blocks detection and workaround
Co-authored-by: Paweł Dziepak <pawel.dziepak@xtxmarkets.com>
