Where is the "heap"?

Question

I just want to know where is (if present!) the Heap of my bash process (pid = 16457) in the result of cat /proc/16457/maps

0078a000-007a0000 r-xp 00000000 08:02 1319336    /lib/ld-2.3.4.so
007a0000-007a1000 r--p 00015000 08:02 1319336    /lib/ld-2.3.4.so
007a1000-007a2000 rw-p 00016000 08:02 1319336    /lib/ld-2.3.4.so
007a9000-008cf000 r-xp 00000000 08:02 1384495    /lib/tls/libc-2.3.4.so
008cf000-008d1000 r--p 00125000 08:02 1384495    /lib/tls/libc-2.3.4.so
008d1000-008d3000 rw-p 00127000 08:02 1384495    /lib/tls/libc-2.3.4.so
008d3000-008d5000 rw-p 008d3000 00:00 0
008fc000-008fe000 r-xp 00000000 08:02 1319337    /lib/libdl-2.3.4.so
008fe000-008ff000 r--p 00001000 08:02 1319337    /lib/libdl-2.3.4.so
008ff000-00900000 rw-p 00002000 08:02 1319337    /lib/libdl-2.3.4.so
00b27000-00b2a000 r-xp 00000000 08:02 278109     /lib/libtermcap.so.2.0.8
00b2a000-00b2b000 rw-p 00002000 08:02 278109     /lib/libtermcap.so.2.0.8
08047000-080d8000 r-xp 00000000 08:02 902412     /bin/bash
080d8000-080de000 rw-p 00090000 08:02 902412     /bin/bash
080de000-080e3000 rw-p 080de000 00:00 0
09ceb000-09d25000 rw-p 09ceb000 00:00 0
b7d99000-b7d9b000 rw-p b7d99000 00:00 0
b7d9b000-b7da1000 r--s 00000000 08:02 130808     /usr/lib/gconv/gconv-modules.cache
b7da1000-b7dd6000 r--s 00000000 08:02 869910     /var/db/nscd/passwd
b7dd6000-b7fd6000 r--p 00000000 08:02 101088     /usr/lib/locale/locale-archive
b7fd6000-b7fd8000 rw-p b7fd6000 00:00 0
bff07000-c0000000 rw-p bff07000 00:00 0
ffffe000-fffff000 r-xp 00000000 00:00 0

Answer 1

The heap usually appears to be marked with [heap] when a malloc call is called; however, you'll notice that if you keep growing the heap with multiple lines of malloc() code that range will not grow; however, new blank line entries will be created.

Answer 2

The heap is clearly marked as [heap] in current Linux versions. Your listing doesn't show it. Are you sure you didn't accidentally cut it out when copying it to your question?

On my shell:

~% grep '\[heap' /proc/$$/maps
00bca000-00d2e000 rw-p 00000000 00:00 0                                  [heap]

Answer 3

"The" heap most people refer to is this line:

080de000-080e3000 rw-p 080de000 00:00 0

i.e. it's the region of memory created and expandable by the brk syscall, immediately following the main program's .data and .bss segments.

One might also consider the following as part of the "heap":

09ceb000-09d25000 rw-p 09ceb000 00:00 0

It seems to be an anonymous mapping created by mmap to service a large malloc request. Most malloc implementations use mmap for large requests so they can munmap it on free and return the whole block of memory to the OS. It also makes calloc much faster since you're guaranteed to get per-zeroed pages this way.