Ubuntu Manpage: move_pages - move individual pages of a process to another node

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 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.

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_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.

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_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.

VERSIONS

       move_pages() first appeared in Linux 2.6.18.

STANDARDS

       This system call is Linux-specific.

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 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.