SLUB vs SLAB allocator

Hi, I found that in many worst case scenarios like fragmention of allocator , slub performs well than slab. I also noticed that Centos /Ubuntu etc switched to SLUB but SLES still uses SLAB in the default image. Any particular reason where SLAB is the choice ? I ask this since i find SLUB to be the default choice since 2.6.23 as per https://en.wikipedia.org/wiki/SLUB_(software) Regards, Navin