Reproduce

1. Prepare test work env.

To generate test files, use TestPrefetrch in smoke/api_test.go.

2. Create a nydusd process.

sudo nydusd --apisock api.sock --config nydusd-config.fusedev.json --mountpoint mnt
Observe the number of threads of the nydusd process:

3. Use the mount api to mount the sub-mount point.

curl --unix-socket api.sock \
     -X POST "http://localhost/api/v1/mount?mountpoint=/sub" \
     -H "Content-Type: application/json" \
     -d '{
        "source":"bootstrap-test",
        "fs_type":"rafs",
        "config":"{\"device\":{\"backend\":{\"type\":\"localfs\",\"config\":{\"dir\":\"blobs\"}},\"cache\":{\"type\":\"blobcache\",\"config\":{\"work_dir\":\"cache\"}}},\"mode\":\"direct\",\"digest_validate\":false}"
	}'

Observe the number of threads of the nydusd process after mount:

4. Umount sub mount point.

curl --unix-socket api.sock \
     -X DELETE "http://localhost/api/v1/mount?mountpoint=/sub"

Observe the number of threads of the nydusd process after umount:

Result:

After mount, the nydusd process creates two cache-flusher threads but only recycles one with umount.

from nydus.