continous healing based on crawler (#10103)

Design: https://gist.github.com/klauspost/792fe25c315caf1dd15c8e79df124914

cmd/data-usage-cache.go

@@ -85,7 +85,12 @@ func (e *dataUsageEntry) merge(other dataUsageEntry) {
 }
 
 // mod returns true if the hash mod cycles == cycle.
+// If cycles is 0 false is always returned.
+// If cycles is 1 true is always returned (as expected).
 func (h dataUsageHash) mod(cycle uint32, cycles uint32) bool {
+	if cycles <= 1 {
+		return cycles == 1
+	}
 	return uint32(xxhash.Sum64String(string(h)))%cycles == cycle%cycles
 }
 
@@ -117,6 +122,16 @@ func (d *dataUsageCache) find(path string) *dataUsageEntry {
 	return &due
 }
 
+// findChildrenCopy returns a copy of the children of the supplied hash.
+func (d *dataUsageCache) findChildrenCopy(h dataUsageHash) dataUsageHashMap {
+	ch := d.Cache[h.String()].Children
+	res := make(dataUsageHashMap, len(ch))
+	for k := range ch {
+		res[k] = struct{}{}
+	}
+	return res
+}
+
 // Returns nil if not found.
 func (d *dataUsageCache) subCache(path string) dataUsageCache {
 	dst := dataUsageCache{Info: dataUsageCacheInfo{