if (s->flags & __CMPXCHG_DOUBLE) { ret = __update_freelist_fast(slab, freelist_old, counters_old, freelist_new, counters_new); } else { ret = __update_freelist_slow(slab, freelist_old, counters_old, freelist_new, counters_new); }
This policy is very similar to annotated code below. The description is reproduced here:
This policy determines if the system has support for compare and exchange. If so, it will use the "__update_freelist_fast()" function, which uses a compare and exchange internally. Otherwise, it will use "__update_freelist_slow()", which uses a lock (specifically a bit-based spinlock) internally.