.\" This manpage is Copyright (C) 2006 Silicon Graphics, Inc.

.\"                               Christoph Lameter

.\"

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.\" manual provided the copyright notice and this permission notice are

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.\" FIXME Should programs normally be using move_pages() directly, or should

.\" they rather be using interfaces in the numactl package?

.\" (e.g., compare with recommendation in mbind(2)).

.\" Does this page need to give advice on this topic?

.\"

.TH MOVE_PAGES 2 2017-09-15 "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>

.PP

.BI "long move_pages(int " pid ", unsigned long count, void **" pages ,

.BI "                const int *" nodes ", int *" status ", int " flags );

.fi

.PP

Link with \fI\-lnuma\fP.

.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.

.PP

.I pid

is the ID of the process in which pages are to be moved.

If

.I pid

is 0, then

.BR move_pages ()

moves pages of the calling process.

.PP

To move pages in another process requires the following privileges:

.IP * 3

In kernels up to and including Linux 4.12:

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.

.IP *

The older rules allowed the caller to discover various

virtual address choices made by the kernel that could lead

to the defeat of address-space-layout randomization

for a process owned by the same UID as the caller,

the rules were changed starting with Linux 4.13.

Since Linux 4.13,

.\" commit 197e7e521384a23b9e585178f3f11c9fa08274b9

permission is governed by a ptrace access mode

.B PTRACE_MODE_READ_REALCREDS

check with respect to the target process; see

.BR ptrace (2).

.PP

.I count

is the number of pages to move.

It defines the size of the three arrays

.IR pages ,

.IR nodes ,

and

.IR status .

.PP

.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 Describe the result if pointers in the 'pages' array are

.\" not aligned to page boundaries

Addresses are specified as seen by the process specified by

.IR pid .

.PP

.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.

.PP

.I status

is an array of integers that return the status of each page.

The array contains valid values only if

.BR move_pages ()

did not return an error.

.PP

.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 .

.SS 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 be moved only 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 filesystem

does not provide a migration function that would allow the move

of dirty pages.

.TP

.B -EINVAL

A dirty page cannot be moved.

The filesystem 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" in the description of the EACCESS error.

.\" 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).

.PP

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.

.PP

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 ().

.PP

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)

.SH COLOPHON

This page is part of release 4.15 of the Linux

.I man-pages

project.

A description of the project,

information about reporting bugs,

and the latest version of this page,

can be found at

\%https://www.kernel.org/doc/man\-pages/.