Name
move_pages — move individual pages of a process to another node
Synopsis
#include <numaif.h>
long
move_pages( |
int pid, |
| unsigned long count, | |
| void **pages, | |
| const int *nodes, | |
| int *status, | |
int flags); |
![[Note]](../stylesheet/note.png) |
Note |
|---|---|
| There is no glibc wrapper for this system call; see NOTES. |
|
|
Note |
|---|---|
|
Link with |
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 status. 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:
-
In kernels 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 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, permission is governed by a ptrace access mode
PTRACE_MODE_READ_REALCREDScheck 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 error.
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
array.
- 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_ALLis 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 subsystem 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 nonfatal 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_MOVEandMPOL_MF_MOVE_ALLwas 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_ALLwithout sufficient privileges (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.
NOTES
Glibc does not provide a wrapper for this system call. 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 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 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 installing
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)
COLOPHON
This page is part of release 5.11 of the Linux 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/.
|
This manpage is Copyright (C) 2006 Silicon Graphics, Inc. Christoph Lameter %%%LICENSE_START(VERBATIM_TWO_PARA) 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. %%%LICENSE_END 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? |