NAME¶

SYNOPSIS¶

#include <numaif.h>

long move_pages(int pid, unsigned long count, void **pages,
                const int *nodes, int *status, int flags);

Link with -lnuma.

DESCRIPTION¶

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_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.

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.

RETURN VALUE¶

ERRORS¶

E2BIG

Too many pages to move.

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.

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.

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.

VERSIONS¶

CONFORMING TO¶

NOTES¶

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¶

COLOPHON¶