move_pages - move individual pages of a process to another node
long move_pages(int pid, unsigned long count, void **pages,
const int *nodes, int *status, int flags);
Link with -lnuma
() 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.
is the ID of the process in which pages are to be moved. If
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
- 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).
is the number of pages to move. It defines the size of the three
, and status
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
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.
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
specify what types of pages to move. MPOL_MF_MOVE
only pages that are in exclusive use by the process are to be moved.
means that pages shared between multiple processes can
also be moved. The process must be privileged (CAP_SYS_NICE
) to use
The following values can be returned in each element of the status
- Identifies the node on which the page resides.
- The page is mapped by multiple processes and can be moved only if
MPOL_MF_MOVE_ALL is specified.
- 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.
- This is a zero page or the memory area is not mapped by the process.
- 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.
- A dirty page cannot be moved. The filesystem does not provide a migration
function and has no ability to write back pages.
- The page is not present.
- Unable to allocate memory on target node.
On success move_pages
() returns zero. On error, it returns -1, and sets
to indicate the error.
- Too many pages to move. Since Linux 2.6.29, the kernel no longer generates
- One of the target nodes is not allowed by the current cpuset.
- Parameter array could not be accessed.
- 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.
- One of the target nodes is not online.
- 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
- Process does not exist.
() first appeared on Linux in version 2.6.18.
This system call is Linux-specific.
For information on library support, see numa
(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
and/or the specified process (See set_mempolicy
(2)). That is, memory
policy does not constrain the destination nodes used by move_pages
header is not included with glibc, but requires
or a similar package.