This will stop being a problem when we actually have btrees, but for now
the fragmentation caused by byte-level syncs was easily enough to
overflow an mdir when cache size is big.
A smaller cache size is also nicer for debugging, since smaller cache
sizes results in data getting flushed to disk earlier, which is easier
to inspect than in-device buffers. And a 16-byte cache still provides
decent test coverage over cache interactions.
---
Also dropped inline_size to block_size/8. I realized while debugging
that opened shrubs take up additional space until we sync, so we need to
expect up to 2 temporary copies of shrubs when writing files.
Christopher Haster
1d92169e5b