Where is the heap?

Question

I understand that in Linux the mm_struct describes the memory layout of a process. I also understand that the start_brk and brk mark the s

Answer 1

I notice the following in the manpage for malloc(3):

Normally, malloc() allocates memory from the heap, and adjusts the size of the heap as required, using sbrk(2). When allocating blocks of memory larger than MMAP_THRESHOLD bytes, the glibc malloc() implementation allocates the memory as a private anonymous mapping using mmap(2). MMAP_THRESHOLD is 128 kB by default, but is adjustable using mallopt(3). Allocations performed using mmap(2) are unaffected by the RLIMIT_DATA resource limit (see getrlimit(2)).

So it sounds like mmap is used instead of the heap.