Make, etc. a dent in something
Definition 1 of 2
Pro Tip 1/3Unwanted Reduction
Used to describe small progress in reducing something negative or excessive. 
We need more than a few volunteers to actually make a dent in the city's pollution.
Pro Tip 2/3Minimal Impact
Implies that while there is some impact, it might not be very significant. 
The discount barely made a dent in the overall price.
Pro Tip 3/3Figurative Use
It's usually metaphorical, not about physical dents. 
Despite our efforts, we hardly made a dent in public opinion.