Given that they are partitioning into cache-line sized blocks, I assume they are partitioning as a time-space tradeoff?
[edit]
Rereading that section more carefully, they are concerned about concurrent write performance to the bloom filter; since two CPUs can not write to the same cache-line in parallel, it's definitely done for performance reasons.
[edit]
Rereading that section more carefully, they are concerned about concurrent write performance to the bloom filter; since two CPUs can not write to the same cache-line in parallel, it's definitely done for performance reasons.