Hello Joey,
So I have another idea to speed up git annex sync --content --all. As far as I understand, the first pass with --all (walking the worktree) is just to make preferred content expressions which include paths (and lackingcopies=) happy. Now, if the preferred content expression of the local repo and of none of the remotes contain paths, that first pass can be skipped. 

I did some benchmarking by replacing the following in seekSyncContent:

    Just WantAllKeys -> Just <$> genBloomFilter (seekworktree mvar (WorkTreeItems []))

with:

    Just WantAllKeys -> pure Nothing

and it led to a 2x speedup (with warm cache):

    before:
    real    0m41.186s

    after:
    real    0m22.182s


This repo has 25641 keys and all of them are in the worktree too.

> [[done]]! --[[Joey]]
