MOVE_PAGES(2)                                       Linux Programmer's Manual                                      MOVE_PAGES(2)



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);

       Link with -lnuma.

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.  To move pages in another process, the caller must be privi-
       leged  (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.  If pid is 0, then move_pages() moves pages of the calling process.

       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 num-
       ber.  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 only contains valid values 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.

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 only be moved 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
              file system does not provide a migration function that would allow the move of dirty pages.

       -EINVAL
              A  dirty  page cannot be moved.  The file system 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.

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 ker-
              nel 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
       move_pages() first appeared on Linux in version 2.6.18.

CONFORMING TO
       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.

SEE ALSO
       get_mempolicy(2), mbind(2), set_mempolicy(2), numa(3), numa_maps(5), cpuset(7), numa(7), migratepages(8), numa_stat(8)

COLOPHON
       This page is part of release 3.25 of the Linux man-pages project.  A description of the project,  and  information  about
       reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                                                      2010-06-11                                              MOVE_PAGES(2)