The actual memory footprint of static_map is larger than my estimation

[Gibyeng]

Hi, I find the memory footprint of cuco::static_map is significantly larger than its theoretical size (capacity* (sizeof(KEY) + sizeof(VALUE))). For instance, I set up a static_map and its theoretical memory footprint is 4.65G. However, it actually consumes 6.20G GPU memory. Why is that?

[Gibyeng]

After a few tests, I find the real reason is memory alignment issue.

[PointKernel]

The alignment of your key and payload types can be one factor, while another is that cuco hash tables ensure the requested capacity serves as a lower bound. They select the smallest prime number greater than the requested capacity as the actual capacity. see

cuCollections/include/cuco/extent.cuh

Lines 95 to 99 in 93d6172

	* @note The actual capacity of a container (map/set) should be exclusively determined by the return
	* value of this utility since the output depends on the requested low-bound size, the probing
	* scheme, and the storage. This utility is used internally during container constructions while for
	* container ref constructions, it would be users' responsibility to use this function to determine
	* the input size of the ref.