move_pages - move individual pages of a process to another node
NUMA (Non-Uniform Memory Access) policy library (
libnuma,
-lnuma)
#include <numaif.h>
long move_pages(int pid, unsigned long count, void *pages[.count],
const int nodes[.count], int status[.count], int flags);
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:
- •
- 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_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
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.
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_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 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.
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.
- 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_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 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.
move_pages() first appeared in Linux 2.6.18.
This system call is Linux-specific.
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.
get_mempolicy(2),
mbind(2),
set_mempolicy(2),
numa(3),
numa_maps(5),
cpuset(7),
numa(7),
migratepages(8),
numastat(8)