bionic (2) move_pages.2.gz

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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

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