.\" Hey Emacs! This file is -*- nroff -*- source.
.\"
.\" This manpage is Copyright (C) 2006 Silicon Graphics, Inc.
.\"                               Christoph Lameter
.\"
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
.\"
.\" FIXME Should programs normally be using this API directly, or should
.\" they rather be using interfaces in the numactl package?
.\" (e.g., compare with recommendation in mbind(2)).
.TH MOVE_PAGES 2 2008-10-06 "Linux" "Linux Programmer's Manual"
.SH NAME
move_pages \- move individual pages of a process to another node
.SH SYNOPSIS
.nf
.B #include <numaif.h>
.sp
.BI "long move_pages(int " pid ", unsigned long count, void **" pages ,
.BI "                const int *" nodes ", int *" status ", int " flags );
.fi
.SH DESCRIPTION
.BR move_pages ()
moves the specified
.I pages
of the process
.I pid
to the memory nodes specified by
.IR nodes .
The result of the move is reflected in
.IR status .
The
.I flags
indicate constraints on the pages to be moved.

.I pid
is the ID of the process in which 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 move_pages ()
moves pages of the calling process.

.I count
is the number of pages to move.
It defines the size of the three arrays
.IR pages ,
.IR nodes ,
and
.IR status .

.I pages
is an array of pointers to the pages that should be moved.
These are pointers that should be aligned to page boundaries.
.\" FIXME what if they are not aligned?
Addresses are specified as seen by the process specified by
.IR pid .

.I nodes
is an array of integers that specify the desired location for each page.
Each element in the array is a node number.
.I nodes
can also be NULL, in which case
.BR move_pages ()
does not move any pages but instead will return the node
where each page currently resides, in the
.I status
array.
Obtaining the status of each page may be necessary to determine
pages that need to be moved.

.I status
is an array of integers that return the status of each page.
The array only contains valid values if
.BR move_pages ()
did not return an error.

.I flags
specify what types of pages to move.
.B MPOL_MF_MOVE
means that only pages that are in exclusive use by the process
are to be moved.
.B MPOL_MF_MOVE_ALL
means that pages shared between multiple processes can also be moved.
The process must be privileged
.RB ( CAP_SYS_NICE )
to use
.BR MPOL_MF_MOVE_ALL .
.SH Page states in the status array
The following values can be returned in each element of the
.I status
array.
.TP
.B 0..MAX_NUMNODES
Identifies the node on which the page resides.
.TP
.B -EACCES
The page is mapped by multiple processes and can only be moved if
.B MPOL_MF_MOVE_ALL
is specified.
.TP
.B -EBUSY
The page is currently busy and cannot be moved.
Try again later.
This occurs if a page is undergoing I/O or another kernel subsystem
is holding a reference to the page.
.TP
.B -EFAULT
This is a zero page or the memory area is not mapped by the process.
.TP
.B -EIO
Unable to write back a page.
The page has to be written back
in order to move it since the page is dirty and the file system
does not provide a migration function that would allow the move
of dirty pages.
.TP
.B -EINVAL
A dirty page cannot be moved.
The file system does not
provide a migration function and has no ability to write back pages.
.TP
.B -ENOENT
The page is not present.
.TP
.B -ENOMEM
Unable to allocate memory on target node.
.SH "RETURN VALUE"
On success
.BR move_pages ()
returns zero.
.\" FIXME Is the following quite true: does the wrapper in numactl
.\" do the right thing?
On error, it returns \-1, and sets
.I errno
to indicate the error.
.SH ERRORS
.TP
.B E2BIG
Too many pages to move.
.TP
.B EACCES
.\" FIXME Clarify "current cpuset".  Is that the cpuset of the caller
.\" or the target?
One of the target nodes is not allowed by the current cpuset.
.TP
.B EFAULT
Parameter array could not be accessed.
.TP
.B EINVAL
Flags other than
.B MPOL_MF_MOVE
and
.B MPOL_MF_MOVE_ALL
was specified or an attempt was made to migrate pages of a kernel thread.
.TP
.B ENODEV
One of the target nodes is not online.
.TP
.B ENOENT
No pages were found that require moving.
All pages are either already
on the target node, not present, had an invalid address or could not be
moved because they were mapped by multiple processes.
.TP
.B EPERM
The caller specified
.B MPOL_MF_MOVE_ALL
without sufficient privileges
.RB ( CAP_SYS_NICE ).
Or, the caller attempted to move pages of a process belonging
to another user but did not have privilege to do so
.RB ( CAP_SYS_NICE ).
.TP
.B ESRCH
Process does not exist.
.SH VERSIONS
.BR move_pages ()
first appeared on Linux in version 2.6.18.
.SH CONFORMING TO
This system call is Linux-specific.
.SH "NOTES"
For information on library support, see
.BR numa (7).

Use
.BR get_mempolicy (2)
with the
.B MPOL_F_MEMS_ALLOWED
flag to obtain the set of nodes that are allowed by
.\" FIXME Clarify "current cpuset".  Is that the cpuset of the caller
.\" or the target?
the current cpuset.
Note that this information is subject to change at any
time by manual or automatic reconfiguration of the cpuset.

Use of this function 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 move_pages ().
.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 numa_stat (8)
.SH COLOPHON
This page is part of release 3.22 of the Linux
.I man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.
