start moving malloc and friends in

README.adoc

@@ -12523,8 +12523,6 @@ Programs under link:userland/c/[] are examples of https://en.wikipedia.org/wiki/
 ** `stdlib.h`
 *** exit
 **** link:userland/c/abort.c[]
-*** malloc
-**** link:userland/c/out_of_memory.c[]
 ** `stdio.h`
 *** link:userland/c/stderr.c[]
 *** link:userland/c/getchar.c[]
@@ -12533,6 +12531,15 @@ Programs under link:userland/c/[] are examples of https://en.wikipedia.org/wiki/
 * Fun
 ** link:userland/c/infinite_loop.c[]
 
+==== malloc
+
+Allocate memory! Vs using the stack: https://stackoverflow.com/questions/4584089/what-is-the-function-of-the-push-pop-instructions-used-on-registers-in-x86-ass/33583134#33583134
+
+* link:userland/c/malloc.c[]: `malloc` hello world: allocate two ints and use them.
+* link:userland/c/out_of_memory.c[]: test how much memory Linux lets us allocate
+
+LInux 5.1 / glibc 2.29 implements it with the <<mmap,`mmap` system call>>.
+
 ==== GCC C extensions
 
 ===== C empty struct
@@ -12629,6 +12636,26 @@ getconf -a
 
 `getconf` is also specified by POSIX at: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/getconf.html but not the `-a` option which shows all configurations.
 
+==== mmap
+
+The mmap system call allows advanced memory operations:
+
+* link:userland/posix/mmap_file.c[]: memory mapped file example
+
+mmap is notably used to implement the <<malloc,malloc ANSI C>> function, replacing the previously used break system call.
+
+Linux adds has several POSIX extension flags to it.
+
+===== brk
+
+Previously <<posix>>, but was deprecated in favor of <<malloc>>
+
+Example: link:userland/glibc/brk.c[]
+
+The example allocates two ints and uses them, and then deallocates back.
+
+Bibliography: https://stackoverflow.com/questions/6988487/what-does-the-brk-system-call-do/31082353#31082353
+
 === Userland multithreading
 
 The following sections are related to multithreading in userland: