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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.  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.

   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.

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 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), numastat(8)

COLOPHON

       This page is part of release 4.16 of the Linux man-pages project.  A  description  of  the
       project,  information  about  reporting  bugs, and the latest version of this page, can be
       found at https://www.kernel.org/doc/man-pages/.