investigate influence of tcmalloc TCMALLOC_TRANSFER_NUM_OBJ setting on memory fragmentation and performance

In MB-11961 we found that -DTCMALLOC_SMALL_BUT_SLOW is actually causing visible degradation in performance.

But in order to try to limit aggressiveness of tcmalloc's trade of memory fragmentation for performance we can still try playing with TCMALLOC_TRANSFER_NUM_OBJ. Specifically because in 2.1 default number of items to transfer was bumped significantly for small memory chunks. Which may negatively affect memory fragmentation.

So we should try to do at least one run wth TCMALLOC_TRANSFER_NUM_OBJ so to 40. We can also play with larger values. I.e. 512 and 4096.