1 .\" Copyright (c) 1996 Tom Bjorkholm <tomb@mydata.se>
3 .\" %%%LICENSE_START(GPLv2+_DOC_FULL)
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24 .\" 1996-04-11 Tom Bjorkholm <tomb@mydata.se>
25 .\" First version written (1.3.86)
26 .\" 1996-04-12 Tom Bjorkholm <tomb@mydata.se>
27 .\" Update for Linux 1.3.87 and later
28 .\" 2005-10-11 mtk: Added NOTES for MREMAP_FIXED; revised EINVAL text.
30 .TH MREMAP 2 2010-06-10 "Linux" "Linux Programmer's Manual"
32 mremap \- remap a virtual memory address
35 .BR "#define _GNU_SOURCE" " /* See feature_test_macros(7) */"
37 .B #include <sys/mman.h>
39 .BI "void *mremap(void *" old_address ", size_t " old_size ,
40 .BI " size_t " new_size ", int " flags ", ... /* void *" new_address " */);"
44 expands (or shrinks) an existing memory mapping, potentially
45 moving it at the same time (controlled by the \fIflags\fP argument and
46 the available virtual address space).
48 \fIold_address\fP is the old address of the virtual memory block that you
49 want to expand (or shrink).
50 Note that \fIold_address\fP has to be page
52 \fIold_size\fP is the old size of the
54 \fInew_size\fP is the requested size of the
55 virtual memory block after the resize.
56 An optional fifth argument,
58 may be provided; see the description of
62 In Linux the memory is divided into pages.
63 A user process has (one or)
64 several linear virtual memory segments.
65 Each virtual memory segment has one
66 or more mappings to real memory pages (in the page table).
67 Each virtual memory segment has its own
68 protection (access rights), which may cause
69 a segmentation violation if the memory is accessed incorrectly (e.g.,
70 writing to a read-only segment).
71 Accessing virtual memory outside of the
72 segments will also cause a segmentation violation.
75 uses the Linux page table scheme.
78 mapping between virtual addresses and memory pages.
79 This can be used to implement a very efficient
82 The \fIflags\fP bit-mask argument may be 0, or include the following flag:
85 By default, if there is not sufficient space to expand a mapping
86 at its current location, then
89 If this flag is specified, then the kernel is permitted to
90 relocate the mapping to a new virtual address, if necessary.
91 If the mapping is relocated,
92 then absolute pointers into the old mapping location
93 become invalid (offsets relative to the starting address of
94 the mapping should be employed).
96 .BR MREMAP_FIXED " (since Linux 2.3.31)"
97 This flag serves a similar purpose to the
101 If this flag is specified, then
103 accepts a fifth argument,
104 .IR "void\ *new_address" ,
105 which specifies a page-aligned address to which the mapping must
107 Any previous mapping at the address range specified by
116 must also be specified.
118 If the memory segment specified by
124 or similar), then this lock is maintained when the segment is
125 resized and/or relocated.
126 As a consequence, the amount of memory locked by the process may change.
130 returns a pointer to the new virtual memory area.
133 (that is, \fI(void\ *)\ \-1\fP) is returned,
134 and \fIerrno\fP is set appropriately.
138 The caller tried to expand a memory segment that is locked,
139 but this was not possible without exceeding the
144 "Segmentation fault." Some address in the range
145 \fIold_address\fP to \fIold_address\fP+\fIold_size\fP is an invalid
146 virtual memory address for this process.
149 even if there exist mappings that cover the
150 whole address space requested, but those mappings are of different types.
153 An invalid argument was given.
154 Possible causes are: \fIold_address\fP was not
155 page aligned; a value other than
167 or the new address range specified by
171 overlapped the old address range specified by
177 was specified without also specifying
181 The memory area cannot be expanded at the current virtual address, and the
183 flag is not set in \fIflags\fP.
184 Or, there is not enough (virtual) memory available.
186 This call is Linux-specific, and should not be used in programs
187 intended to be portable.
188 .\" 4.2BSD had a (never actually implemented)
190 .\" call with completely different semantics.
192 Prior to version 2.4, glibc did not expose the definition of
194 and the prototype for
196 did not allow for the
209 Your favorite text book on operating systems
210 for more information on paged memory
211 (e.g., \fIModern Operating Systems\fP by Andrew S. Tanenbaum,
212 \fIInside Linux\fP by Randolf Bentson,
213 \fIThe Design of the UNIX Operating System\fP by Maurice J. Bach)
215 This page is part of release 3.68 of the Linux
218 A description of the project,
219 information about reporting bugs,
220 and the latest version of this page,
222 \%http://www.kernel.org/doc/man\-pages/.