"opt.tcache" (bool) r- [--enable-tcache]
        Thread-specific caching (tcache) enabled/disabled. When there are multiple threads, each thread uses a tcache for objects up to a certain size. Thread-specific caching allows many allocations to be satisfied without performing any
        thread synchronization, at the cost of increased memory use. See the "opt.lg_tcache_max" option for related tuning information. This option is enabled by default unless running inside Valgrind[2], in which case it is forcefully
        disabled.

"opt.lg_tcache_max" (size_t) r- [--enable-tcache]
    Maximum size class (log base 2) to cache in the thread-specific cache (tcache). At a minimum, all small size classes are cached, and at a maximum all large size classes are cached. The default maximum is 32 KiB (2^15).
struct tcache_s {
	ql_elm(tcache_t) link;		/* Used for aggregating stats. */
	uint64_t	prof_accumbytes;/* Cleared after arena_prof_accum(). */
	unsigned	ev_cnt;		/* Event count since incremental GC. */
	szind_t		next_gc_bin;	/* Next bin to GC. */
	tcache_bin_t	tbins[1];	/* Dynamically sized. */
	/*
	 * The pointer stacks associated with tbins follow as a contiguous
	 * array.  During tcache initialization, the avail pointer in each
	 * element of tbins is initialized to point to the proper offset within
	 * this array.
	 */
};

struct tcache_bin_s {
	tcache_bin_stats_t tstats;
	int		low_water;	/* Min # cached since last GC. */
	unsigned	lg_fill_div;	/* Fill (ncached_max >> lg_fill_div). */
	unsigned	ncached;	/* # of cached objects. */
	void		**avail;	/* Stack of available objects. */
};