move_pages

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  sta-
       tus.  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 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.

       *  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  ker-
              nel 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  pro-
              cesses.

       EPERM  The  caller specified MPOL_MF_MOVE_ALL without sufficient privi-
              leges (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 4.15 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/.

Linux                             2017-09-15                     MOVE_PAGES(2)
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