When I start a batch operation on many files, like thumbnailing a quite large collection (41GB), Digikam starts to increase both its virtual memory and resident memory usage, up to the point in which I have to kill it, since the system starts thrashing (I have 8GB of RAM).

Reproducible: Always

Steps to Reproduce:
1. add a large collection of pictures as a source
2. request tools->maintenance->thumbnail creation
3. look at RAM using top
Actual Results:  
VM and RSS RAM usage starts increasing.

Expected Results:  
Use smaller batches to avoid filling up all RAM