After SERVER-23069, the size of the TCMalloc section in serverStatus has grown substantially with the addition of per-size class statistics (roughly 10-11 kB). This negatively affects FTDC data retention.

It would be nice to be able to tune the level of detail with which we get TCMalloc statistics; for example,

• tcmalloc: 1 returns the original level of detail prior to SERVER-23069 without size class information;
• tcmalloc: 2 includes additional size class information;
• tcmalloc: 3 includes the TCMalloc `DumpStats` text blob;

and so on. (This behavior would also be backwards-compatible for people already specifying tcmalloc: 1 to serverStatus.)