move_pages(2) System Calls Manual move_pages(2)
NAME
move_pages - move individual pages of a process to another node
LIBRARY
NUMA (Non-Uniform Memory Access) policy library (libnuma, -lnuma)
SYNOPSIS
#include <numaif.h>
long move_pages(int pid, unsigned long count, void *pages[.count],
const int nodes[.count], int status[.count], int flags);
DESCRIPTION
move_pages() moves the specified pages of the process pid to the memory
nodes specified by nodes. The result of the move is reflected in sta-
tus. The flags indicate constraints on the pages to be moved.
pid is the ID of the process in which pages are to be moved. If pid is
0, then move_pages() moves pages of the calling process.
To move pages in another process requires the following privileges:
• Up to and including Linux 4.12: the caller must be privileged
(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.
• The older rules allowed the caller to discover various virtual ad-
dress choices made by the kernel that could lead to the defeat of ad-
dress-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, permission is governed by a ptrace access mode
PTRACE_MODE_READ_REALCREDS check with respect to the target process;
see ptrace(2).
count is the number of pages to move. It defines the size of the three
arrays pages, nodes, and status.
pages is an array of pointers to the pages that should be moved. These
are pointers that should be aligned to page boundaries. Addresses are
specified as seen by the process specified by pid.
nodes is an array of integers that specify the desired location for each
page. Each element in the array is a node number. nodes can also be
NULL, in which case move_pages() does not move any pages but instead
will return the node where each page currently resides, in the status
array. Obtaining the status of each page may be necessary to determine
pages that need to be moved.
status is an array of integers that return the status of each page. The
array contains valid values only if move_pages() did not return an er-
ror. Preinitialization of the array to a value which cannot represent a
real numa node or valid error of status array could help to identify
pages that have been migrated.
flags specify what types of pages to move. MPOL_MF_MOVE means that only
pages that are in exclusive use by the process are to be moved.
MPOL_MF_MOVE_ALL means that pages shared between multiple processes can
also be moved. The process must be privileged (CAP_SYS_NICE) to use
MPOL_MF_MOVE_ALL.
Page states in the status array
The following values can be returned in each element of the status ar-
ray.
0..MAX_NUMNODES
Identifies the node on which the page resides.
-EACCES
The page is mapped by multiple processes and can be moved only if
MPOL_MF_MOVE_ALL is specified.
-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 subsys-
tem is holding a reference to the page.
-EFAULT
This is a zero page or the memory area is not mapped by the
process.
-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.
-EINVAL
A dirty page cannot be moved. The filesystem does not provide a
migration function and has no ability to write back pages.
-ENOENT
The page is not present.
-ENOMEM
Unable to allocate memory on target node.
RETURN VALUE
On success move_pages() returns zero. On error, it returns -1, and sets
errno to indicate the error. If positive value is returned, it is the
number of nonmigrated pages.
ERRORS
Positive value
The number of nonmigrated pages if they were the result of nonfa-
tal reasons (since Linux 4.17).
E2BIG Too many pages to move. Since Linux 2.6.29, the kernel no longer
generates this error.
EACCES One of the target nodes is not allowed by the current cpuset.
EFAULT Parameter array could not be accessed.
EINVAL Flags other than MPOL_MF_MOVE and MPOL_MF_MOVE_ALL was specified
or an attempt was made to migrate pages of a kernel thread.
ENODEV One of the target nodes is not online.
EPERM The caller specified MPOL_MF_MOVE_ALL without sufficient privi-
leges (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 (CAP_SYS_NICE).
ESRCH Process does not exist.
STANDARDS
Linux.
HISTORY
Linux 2.6.18.
NOTES
For information on library support, see numa(7).
Use get_mempolicy(2) with the MPOL_F_MEMS_ALLOWED flag to obtain the set
of nodes that are allowed by the current cpuset. Note that this infor-
mation is subject to change at any time by manual or automatic reconfig-
uration of the cpuset.
Use of this function may result in pages whose location (node) violates
the memory policy established for the specified addresses (See mbind(2))
and/or the specified process (See set_mempolicy(2)). That is, memory
policy does not constrain the destination nodes used by move_pages().
The <numaif.h> header is not included with glibc, but requires in-
stalling libnuma-devel or a similar package.
SEE ALSO
get_mempolicy(2), mbind(2), set_mempolicy(2), numa(3), numa_maps(5),
cpuset(7), numa(7), migratepages(8), numastat(8)
Linux man-pages 6.9.1 2024-05-02 move_pages(2)
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