MREMAP(2) Linux Programmer's Manual MREMAP(2)
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
virtual memory block. new_size is the requested size of the virtual memory block after
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 segment has its own protection
(access rights), which may cause a segmentation violation if the memory is accessed incor-
rectly (e.g., writing to a read-only segment). Accessing virtual memory outside of the
segments will also cause a segmentation violation.
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 appropriately.
EINVAL An invalid argument was given. Most likely old_address was not page aligned.
EFAULT "Segmentation fault." Some address in the range old_address to old_address+old_size
is an invalid virtual 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.
EAGAIN The memory segment is locked and cannot be re-mapped.
ENOMEM The memory area cannot be expanded at the current virtual address, and the
MREMAP_MAYMOVE flag is not set in flags. Or, there is not enough (virtual) memory
With current glibc includes, in order to get the definition of MREMAP_MAYMOVE, you need to
define _GNU_SOURCE before including <sys/mman.h>.
This call is Linux-specific, and should not be used in programs 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), mmap(2)
Your favorite OS text book for more information on paged memory. (Modern Operating Sys-
tems by Andrew S. Tannenbaum, Inside Linux by Randolf Bentson, The Design of the UNIX
Operating System by Maurice J. Bach.)
Linux 1.3.87 1996-04-12 MREMAP(2)