mremap - re-map a virtual memory address
void * mremap(void * old_address, size_t old_size , size_t
new_size, unsigned long flags));
mremap expands (or shrinks) an existing memory mapping,
potentially moving it at the same time (controlled by the
flags argument and the available virtual address space).
old_address is the old address of the virtual memory block
that you want to expand (or shrink). Note that old_address
has to be page aligned. old_size is the old size of the vir-
tual memory block. new_size is the requested size of the
virtual memory block after the resize.
The flags argument is a bitmap of flags.
In Linux the memory is divided into pages. A user process
has (one or) several linear virtual memory segments. Each
virtual memory segment has one or more mappings to real
memory pages (in the page table). Each virtual memory seg-
ment has its own protection (access rights), which may cause
a segmentation violation if the memory is accessed
incorrectly (e.g., writing to a read-only segment). Access-
ing virtual memory outside of the segments will also cause a
mremap uses the Linux page table scheme. mremap changes the
mapping between virtual addresses and memory pages. This
can be used to implement a very efficient realloc.
indicates if the operation should fail, or change the
virtual address if the resize cannot be done at the
current virtual address.
On success mremap returns a pointer to the new virtual
memory area. On error, -1 is returned, and errno is set
An invalid argument was given. Most likely old_address
was not page aligned.
"Segmentation fault." Some address in the range
old_address to old_address+old_size is an invalid vir-
tual memory address for this process. You can also get
EFAULT even if there exist mappings that cover the
whole address space requested, but those mappings are
of different types.
The memory segment is locked and cannot be re-mapped.
The memory area cannot be expanded at the current vir-
tual address, and the MREMAP_MAYMOVE flag is not set in
flags. Or, there is not enough (virtual) memory avail-
This call is Linux-specific, and should not be used in pro-
grams intended to be portable. 4.2BSD had a (never actually
implemented) mremap(2) call with completely different seman-
getpagesize(2), realloc(3), malloc(3), brk(2), sbrk(2),
Your favorite OS text book for more information on paged
memory. (Modern Operating Systems by Andrew S. Tannenbaum,
Inside Linux by Randolf Bentson, The Design of the UNIX
Operating System by Maurice J. Bach.)