Section: Linux Programmer's Manual (2)
mremap - remap a virtual memory address
#define _GNU_SOURCE /* See feature_test_macros(7) */
void *mremap(void *old_address, size_t old_size,
size_t new_size, int flags, ... /* void *new_address */);
expands (or shrinks) an existing memory mapping, potentially
moving it at the same time (controlled by the flags
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
old_size is the old size of the
virtual memory block.
new_size is the requested size of the
virtual memory block after the resize.
An optional fifth argument,
may be provided; see the description of
If the value of old_size is zero, and old_address refers to
a shareable mapping (see
will create a new mapping of the same pages.
will be the size of the new mapping and the location of the new mapping
may be specified with new_address; see the description of
If a new mapping is requested via this method, then the
flag must also be specified.
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 incorrectly (e.g.,
writing to a read-only segment).
Accessing virtual memory outside of the
segments will also cause a segmentation violation.
uses the Linux page table scheme.
mapping between virtual addresses and memory pages.
This can be used to implement a very efficient
The flags bit-mask argument may be 0, or include the following flag:
By default, if there is not sufficient space to expand a mapping
at its current location, then
If this flag is specified, then the kernel is permitted to
relocate the mapping to a new virtual address, if necessary.
If the mapping is relocated,
then absolute pointers into the old mapping location
become invalid (offsets relative to the starting address of
the mapping should be employed).
- MREMAP_FIXED (since Linux 2.3.31)
This flag serves a similar purpose to the
If this flag is specified, then
accepts a fifth argument,
which specifies a page-aligned address to which the mapping must
Any previous mapping at the address range specified by
is specified, then
must also be specified.
If the memory segment specified by
is locked (using
or similar), then this lock is maintained when the segment is
resized and/or relocated.
As a consequence, the amount of memory locked by the process may change.
returns a pointer to the new virtual memory area.
On error, the value
(that is, (void *) -1
) is returned,
is set appropriately.
The caller tried to expand a memory segment that is locked,
but this was not possible without exceeding the
"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
even if there exist mappings that cover the
whole address space requested, but those mappings are of different types.
An invalid argument was given.
Possible causes are:
old_address was not
a value other than
was specified in
the new address range specified by
overlapped the old address range specified by
was specified without also specifying
old_size was zero and old_address does not refer to a
shareable mapping (but see BUGS);
old_size was zero and the
flag was not specified.
The memory area cannot be expanded at the current virtual address, and the
flag is not set in flags.
Or, there is not enough (virtual) memory available.
This call is Linux-specific, and should not be used in programs
intended to be portable.
Prior to version 2.4, glibc did not expose the definition of
and the prototype for
did not allow for the
is used to move or expand an area locked with
or equivalent, the
call will make a best effort to populate the new area but will not fail
if the area cannot be populated.
Before Linux 4.14,
was zero and the mapping referred to by
was a private mapping
created a new private mapping unrelated to the original mapping.
This behavior was unintended
and probably unexpected in user-space applications
(since the intention of
is to create a new mapping based on the original mapping).
Since Linux 4.14,
fails with the error
in this scenario.
Your favorite text book on operating systems
for more information on paged memory
(e.g., Modern Operating Systems by Andrew S. Tanenbaum,
Inside Linux by Randolf Bentson,
The Design of the UNIX Operating System by Maurice J. Bach)
This page is part of release 5.04 of the Linux
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at