You can see the memory map for a process through the proc filesystem. As an example, here is the map for the init process, PID 1:

# cat /proc/1/maps
00008000-0000e000 r-xp 00000000 00:0b 23281745   /sbin/init
00016000-00017000 rwxp 00006000 00:0b 23281745   /sbin/init
00017000-00038000 rwxp 00000000 00:00 0          [heap]
b6ded000-b6f1d000 r-xp 00000000 00:0b 23281695   /lib/libc-2.19.so
b6f1d000-b6f24000 ---p 00130000 00:0b 23281695   /lib/libc-2.19.so
b6f24000-b6f26000 r-xp 0012f000 00:0b 23281695   /lib/libc-2.19.so
b6f26000-b6f27000 rwxp 00131000 00:0b 23281695   /lib/libc-2.19.so
b6f27000-b6f2a000 rwxp 00000000 00:00 0
b6f2a000-b6f49000 r-xp 00000000 00:0b 23281359   /lib/ld-2.19.so
b6f4c000-b6f4e000 rwxp 00000000 00:00 0
b6f4f000-b6f50000 r-xp 00000000 00:00 0          [sigpage]
b6f50000-b6f51000 r-xp 0001e000 00:0b 23281359   /lib/ld-2.19.so
b6f51000-b6f52000 rwxp 0001f000 00:0b 23281359   /lib/ld-2.19.so
beea1000-beec2000 rw-p 00000000 00:00 0          [stack]
ffff0000-ffff1000 r-xp 00000000 00:00 0          [vectors]

The first three columns show the start and end virtual addresses and the permissions for each mapping. The permissions are shown here:

If the mapping is associated with a file, the filename appears in the final column, and columns four, five, and six contain the offset from the start of the file, the block device number and the inode of the file. Most of the mappings are to the program itself and the libraries it is linked with. There are two areas where the program can allocate memory, marked [heap] and [stack]. Memory allocated using malloc(3) comes from the former (except for very large allocations, which we will come to later) ; allocations on the stack come from the latter. The maximum size of both areas is controlled by the process's ulimit:

Allocations that exceed the limit are rejected by SIGSEGV.

When running out of memory, the kernel may decide to discard pages that are mapped to a file and are read-only. If that page is accessed again, it will cause a major page fault and be read back in from the file.