Our Jenkins jobs archive quite a lot of artifacts, and we've been running our jobs for a couple of years. As a result, under our jobs directory there are tens of millions of files and directories.
When activating the SCM Sync Configuration Plugin on such a large directory, it will scan for files that matches the pattern **/jobs/*/config.xml under the root directory Hudson.getInstance().getRootDir(). The initial ** segment makes this scan recursive, and every directory has to be traversed.
In our Jenkins installation, the SCM Sync Configuration Plugin never completes the scan, the data to scan is simply too large. I gave up after a couple of hours of scanning and aborted it.
The jobs directory is hardcoded in Jenkins core to be located at Jenkins.getInstance().getRootDir() + "jobs". See jenkins.model.Jenkins.getRootDirFor(String name) for an example. So, as far as I can see, there is no use for the initial ** segment in the pattern.
I suggest that the pattern is narrowed to improve the performance of the initial scan. By changing the PATTERNS constant in hudson.plugins.scm_sync_configuration.strategies.impl.JobConfigScmSyncStrategy to jobs/*/config.xml, the scan is no longer recursive. I've tested this change on our Jenkins installation, and it allows the scan to finish within seconds as opposed to hours.