It's unclear what you're estimating the size of. PAGEVEC_SIZE of 62
mapping->tree_lock is affected as well as zone->lru_lock. The workload
obviously has to touch the relevant locks for pagevecs to be relevant;
however, the primary factor in the effectiveness of pagevecs is the
lock transfer time, which is not likely to vary significantly on boxen
such as the OSDL STP machines. You should use a workload stressing
mapping->tree_lock via codepaths using radix_tree_gang_lookup() and
getting runtime on OSDL's NUMA-Q or otherwise asking SGI to test its
effects, otherwise you're dorking around with boxen with identical
characteristics as far as batched locking is concerned.