1 .\" Hey Emacs! This file is -*- nroff -*- source.
3 .\" Copyright (c) 1996 Tom Bjorkholm <tomb@mydata.se>
5 .\" This is free documentation; you can redistribute it and/or
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22 .\" Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111,
25 .\" 1996-04-11 Tom Bjorkholm <tomb@mydata.se>
26 .\" First version written (1.3.86)
27 .\" 1996-04-12 Tom Bjorkholm <tomb@mydata.se>
28 .\" Update for Linux 1.3.87 and later
29 .\" 2005-10-11 mtk: Added NOTES for MREMAP_FIXED; revised EINVAL text.
31 .TH MREMAP 2 2010-06-10 "Linux" "Linux Programmer's Manual"
33 mremap \- remap a virtual memory address
36 .BR "#define _GNU_SOURCE" " /* See feature_test_macros(7) */"
38 .B #include <sys/mman.h>
40 .BI "void *mremap(void *" old_address ", size_t " old_size ,
41 .BI " size_t " new_size ", int " flags ", ... /* void *" new_address " */);"
45 expands (or shrinks) an existing memory mapping, potentially
46 moving it at the same time (controlled by the \fIflags\fP argument and
47 the available virtual address space).
49 \fIold_address\fP is the old address of the virtual memory block that you
50 want to expand (or shrink).
51 Note that \fIold_address\fP has to be page
53 \fIold_size\fP is the old size of the
55 \fInew_size\fP is the requested size of the
56 virtual memory block after the resize.
57 An optional fifth argument,
59 may be provided; see the description of
63 In Linux the memory is divided into pages.
64 A user process has (one or)
65 several linear virtual memory segments.
66 Each virtual memory segment has one
67 or more mappings to real memory pages (in the page table).
68 Each virtual memory segment has its own
69 protection (access rights), which may cause
70 a segmentation violation if the memory is accessed incorrectly (e.g.,
71 writing to a read-only segment).
72 Accessing virtual memory outside of the
73 segments will also cause a segmentation violation.
76 uses the Linux page table scheme.
79 mapping between virtual addresses and memory pages.
80 This can be used to implement a very efficient
83 The \fIflags\fP bit-mask argument may be 0, or include the following flag:
86 By default, if there is not sufficient space to expand a mapping
87 at its current location, then
90 If this flag is specified, then the kernel is permitted to
91 relocate the mapping to a new virtual address, if necessary.
92 If the mapping is relocated,
93 then absolute pointers into the old mapping location
94 become invalid (offsets relative to the starting address of
95 the mapping should be employed).
97 .BR MREMAP_FIXED " (since Linux 2.3.31)"
98 This flag serves a similar purpose to the
102 If this flag is specified, then
104 accepts a fifth argument,
105 .IR "void *new_address" ,
106 which specifies a page-aligned address to which the mapping must
108 Any previous mapping at the address range specified by
117 must also be specified.
119 If the memory segment specified by
125 or similar), then this lock is maintained when the segment is
126 resized and/or relocated.
127 As a consequence, the amount of memory locked by the process may change.
131 returns a pointer to the new virtual memory area.
134 (that is, \fI(void\ *)\ \-1\fP) is returned,
135 and \fIerrno\fP is set appropriately.
139 The caller tried to expand a memory segment that is locked,
140 but this was not possible without exceeding the
145 "Segmentation fault." Some address in the range
146 \fIold_address\fP to \fIold_address\fP+\fIold_size\fP is an invalid
147 virtual memory address for this process.
150 even if there exist mappings that cover the
151 whole address space requested, but those mappings are of different types.
154 An invalid argument was given.
155 Possible causes are: \fIold_address\fP was not
156 page aligned; a value other than
168 or the new address range specified by
172 overlapped the old address range specified by
178 was specified without also specifying
182 The memory area cannot be expanded at the current virtual address, and the
184 flag is not set in \fIflags\fP.
185 Or, there is not enough (virtual) memory available.
187 This call is Linux-specific, and should not be used in programs
188 intended to be portable.
189 .\" 4.2BSD had a (never actually implemented)
191 .\" call with completely different semantics.
193 Prior to version 2.4, glibc did not expose the definition of
195 and the prototype for
197 did not allow for the
210 Your favorite OS text book for more information on paged memory.
211 (\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.)