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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);

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  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.  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 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 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 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
       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 cur-
       rent cpuset.  Note that this information is subject to change at any time by manual or  automatic  reconfigura-
       tion 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().

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 3.22 of the Linux man-pages project.  A description of the project,  and  informa-
       tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                             2008-10-06                     MOVE_PAGES(2)