bcachefs: add counters for failed shrinker reclaim

This adds distinct counters for every reason the btree node shrinker can
fail to free an object - if our shrinker isn't making progress, this
will tell us why.

Signed-off-by: Daniel Hill <daniel@gluo.nz>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
4 files changed