MREMAP(2)						     Linux Programmer's Manual							 MREMAP(2)

NAME

       mremap - remap a virtual memory address

SYNOPSIS

       #define _GNU_SOURCE
       #include <sys/mman.h>

       void *mremap(void *old_address, size_t old_size,
		    size_t new_size, int flags, ... /* void *new_address */);

DESCRIPTION

       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
       resize.	An optional fifth argument, new_address, may be provided; see the description of MREMAP_FIXED below.

       In Linux the memory is divided into pages.  A user process has (one or) several linear virtual memory segments.	Each virtual  memory  seg-
       ment  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.

       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(3).

       The flags bit-mask argument may be 0, or include the following flag:

       MREMAP_MAYMOVE
	      By default, if there is not sufficient space to expand a mapping at its current location, then mremap()  fails.	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 relo-
	      cated, 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 MAP_FIXED flag of mmap(2).  If this flag is specified, then mremap() accepts a fifth argu-
	      ment, void *new_address, which specifies a page-aligned address to which the mapping must be moved.  Any	previous  mapping  at  the
	      address  range  specified  by  new_address and new_size is unmapped.  If MREMAP_FIXED is specified, then MREMAP_MAYMOVE must also be
	      specified.

       If the memory segment specified by old_address and old_size is locked (using mlock(2) 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.

RETURN VALUE

       On  success  mremap() returns a pointer to the new virtual memory area.	On error, the value MAP_FAILED (that is, (void *) -1) is returned,
       and errno is set appropriately.

ERRORS

       EAGAIN The caller tried to expand a memory segment that is locked, but this was not possible without exceeding the RLIMIT_MEMLOCK  resource
	      limit.

       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.

       EINVAL An  invalid  argument  was  given.   Possible  causes  are:  old_address	was not page aligned; a value other than MREMAP_MAYMOVE or
	      MREMAP_FIXED was specified in flags; new_size was zero; new_size or new_address was invalid; or the new address range  specified	by
	      new_address and new_size overlapped the old address range specified by old_address and old_size; or MREMAP_FIXED was specified with-
	      out also specifying MREMAP_MAYMOVE.

       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 available.

CONFORMING TO

       This call is Linux-specific, and should not be used in programs intended to be portable.

NOTES

       Prior to version 2.4, glibc did not expose the definition of MREMAP_FIXED, and the prototype for mremap() did not allow for the new_address
       argument.

SEE ALSO

       brk(2), getpagesize(2), getrlimit(2), mlock(2), mmap(2), sbrk(2), malloc(3), realloc(3), feature_test_macros(7)

       Your favorite OS text book for more information on paged memory.  (Modern Operating Systems by Andrew S. Tannenbaum, Inside Linux  by  Ran-
       dolf Bentson, The Design of the UNIX Operating System by Maurice J. Bach.)

COLOPHON

       This  page is part of release 3.27 of the Linux man-pages project.  A description of the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

Linux								    2010-06-10								 MREMAP(2)