Question: I have successfully created a big repo made of a few subrepos with git-subtree, let's say Master contains Slave1 and Slave2.

Master/
 Slave1/
 Slave2/

Now I want to tag on Master and push each tag to the slave repos, how can I do it?

If I "git push Slave2 --tags" the entire tag is transferred, but I only want the files related to Slave2 to be transferred.

You can achieve it with git-subsplit, but it's honestly a bit unpractical and slow.

Any suggestion?

Answer: 
I have a solution using git subtree split

All is done on the Master Repository, you can use any branch of the Master.

First create the tag on Master repository
-----------------------------------------

```
git tag -a 1.0.0 -m "the tag 1.0.0"

```

Create the tag for the Slave1
-----------------------------

checkout the tag

```
git checkout 1.0.0

```

Create a branch containing only slave1 for this tag

```
git subtree split --prefix=Slave1 -b slave1_br_1.0.0

```

Create the tag on this branch

```
git checkout slave1_br_1.0.0
git tag -a slave1_tag_1.0.0 -m "the tag 1.0.0"

```

Push the tag on the Slave1 repository

```
git push slave1 slave1_tag_1.0.0:1.0.0

```

Clean the Master repository
---------------------------

Clean the branch

```
git checkout master
git branch -D slave1_br_1.0.0
git tag -d slave1_tag_1.0.0
git gc --prune=now

```

Finally you will have on the Slave1 repository a tag at the same commit than the Master repository with the same name, here 1.0.0

The thing that IMHO is better is that there is no other branch appart from the temporary branch created for this (only the tag is pushed)
I found this in a hard way. 

**When using subtree, the commit in the subtree repo will have a different SHA.** 

So you only need to push the commits to subtree, then locate **the specific commit in subtree repo** that you want to tagged, tag it and push to the subtree repo.

My setup is using sourcetree and github.com, but I think it should be same with other cases.

1. I have a main repo that sync to bitbucket, and a subfolder setup as subtree, sync to github repo.
2. I use this custom action in sourcetree to push the subtree

script to run: `git`

Parameters: `shiny/app` is my subfolder, webapp is my github repo remote name

```
subtree push -P shiny/app webapp master --squash

```

3. Find the specific commit in the subtree branch, tag it and push the tag to the subtree repo.

This is much easier and cleaner than all the answers above. Of course the tag is limited to the subtree instead of full repo, but I think this is what I want.