Hello,
while reading the release notes of git 2.11 I noticed a cool new feature has been merged:
If the filter command (a string value) is defined via
filter.<driver>.processthen Git can process all blobs with a single filter invocation for the entire life of a single Git command.
see the git documentation.
This has been developed in the context of git-lfs (see PR 1382).
If I understand correctly how it works this could speed up v6 repos. Looking at the history/website of git-annex there doesn't seem to be yet any work on this so I though it was worth calling the attention on the feature.
Thanks a lot for all the work on git-annex, it's a really amazing project! The more I study it the more cool features I discover 
Yes, this will make smudge faster when eg checking out a lot of working tree changes. I will need to add support for it.
The "filterdriver" branch implements support for these.
However, it's actually slower than the old interface, because the new interface requires git-annex read the whole file content from git when adding a file, and the old interface let it not read any content.
Since the new interface does have capabilities, a new capability could prevent schepping the content over the pipe, and let the filter driver refer to the worktree file instead, and respond with the path of a file. This would be similar to my old patch set for the old interface.