.\" SPDX-License-Identifier: Linux-man-pages-copyleft-2-para
.\"
.\" Copyright 2009 Intel Corporation
.\"                Author: Andi Kleen
.\" Based on the move_pages manpage which was
.\" This manpage is Copyright (C) 2006 Silicon Graphics, Inc.
.\"                               Christoph Lameter
.\"
.TH migrate_pages 2 2024-05-02 "Linux man-pages 6.8"
.SH NAME
migrate_pages \- move all pages in a process to another set of nodes
.SH LIBRARY
NUMA (Non-Uniform Memory Access) policy library
.RI ( libnuma ", " \-lnuma )
.SH SYNOPSIS
.nf
.B #include <numaif.h>
.P
.BI "long migrate_pages(int " pid ", unsigned long " maxnode,
.BI "                   const unsigned long *" old_nodes,
.BI "                   const unsigned long *" new_nodes );
.fi
.SH DESCRIPTION
.BR migrate_pages ()
attempts to move all pages of the process
.I pid
that are in memory nodes
.I old_nodes
to the memory nodes in
.IR new_nodes .
Pages not located in any node in
.I old_nodes
will not be migrated.
As far as possible,
the kernel maintains the relative topology relationship inside
.I old_nodes
during the migration to
.IR new_nodes .
.P
The
.I old_nodes
and
.I new_nodes
arguments are pointers to bit masks of node numbers, with up to
.I maxnode
bits in each mask.
These masks are maintained as arrays of unsigned
.I long
integers (in the last
.I long
integer, the bits beyond those specified by
.I maxnode
are ignored).
The
.I maxnode
argument is the maximum node number in the bit mask plus one (this is the same
as in
.BR mbind (2),
but different from
.BR select (2)).
.P
The
.I pid
argument is the ID of the process whose pages are to be moved.
To move pages in another process,
the caller must be privileged
.RB ( CAP_SYS_NICE )
or the real or effective user ID of the calling process must match the
real or saved-set user ID of the target process.
If
.I pid
is 0, then
.BR migrate_pages ()
moves pages of the calling process.
.P
Pages shared with another process will be moved only if the initiating
process has the
.B CAP_SYS_NICE
privilege.
.SH RETURN VALUE
On success
.BR migrate_pages ()
returns the number of pages that could not be moved
(i.e., a return of zero means that all pages were successfully moved).
On error, it returns \-1, and sets
.I errno
to indicate the error.
.SH ERRORS
.TP
.B EFAULT
Part or all of the memory range specified by
.IR old_nodes / new_nodes
and
.I maxnode
points outside your accessible address space.
.TP
.B EINVAL
The value specified by
.I maxnode
exceeds a kernel-imposed limit.
.\" As at 3.5, this limit is "a page worth of bits", e.g.,
.\" 8 * 4096 bits, assuming a 4kB page size.
Or,
.I old_nodes
or
.I new_nodes
specifies one or more node IDs that are
greater than the maximum supported node ID.
Or, none of the node IDs specified by
.I new_nodes
are on-line and allowed by the process's current cpuset context,
or none of the specified nodes contain memory.
.TP
.B EPERM
Insufficient privilege
.RB ( CAP_SYS_NICE )
to move pages of the process specified by
.IR pid ,
or insufficient privilege
.RB ( CAP_SYS_NICE )
to access the specified target nodes.
.TP
.B ESRCH
No process matching
.I pid
could be found.
.\" FIXME Document the other errors that can occur for migrate_pages()
.SH STANDARDS
Linux.
.SH HISTORY
Linux 2.6.16.
.SH NOTES
For information on library support, see
.BR numa (7).
.P
Use
.BR get_mempolicy (2)
with the
.B MPOL_F_MEMS_ALLOWED
flag to obtain the set of nodes that are allowed by
the calling process's cpuset.
Note that this information is subject to change at any
time by manual or automatic reconfiguration of the cpuset.
.P
Use of
.BR migrate_pages ()
may result in pages whose location
(node) violates the memory policy established for the
specified addresses (see
.BR mbind (2))
and/or the specified process (see
.BR set_mempolicy (2)).
That is, memory policy does not constrain the destination
nodes used by
.BR migrate_pages ().
.P
The
.I <numaif.h>
header is not included with glibc, but requires installing
.I libnuma\-devel
or a similar package.
.SH SEE ALSO
.BR get_mempolicy (2),
.BR mbind (2),
.BR set_mempolicy (2),
.BR numa (3),
.BR numa_maps (5),
.BR cpuset (7),
.BR numa (7),
.BR migratepages (8),
.BR numastat (8)
.P
.I Documentation/vm/page_migration.rst
in the Linux kernel source tree