There is the idea floating around to do this for the main thread (especially for audit mode, where the automatic static TLS size discovery does not work due to the way the audit interfaces are defined, it's not merely an implementation limitation). This would allow for adjustment of initial-exec TLS expectations if the critical dlopen calls happen before the process goes multi-threaded. For threads created with pthread_create, the TCB is still at the top of the stack, which is quite efficient for access. Moving that would probably consume a TLB slot. Spacing things far apart due to aggressive address space reservations will impact TLB miss performance.