noble (2) move_pages.2.gz

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NAME

       move_pages - move individual pages of a process to another node

LIBRARY

       NUMA (Non-Uniform Memory Access) policy library (libnuma, -lnuma)

SYNOPSIS

       #include <numaif.h>

       long move_pages(int pid, unsigned long count, void *pages[.count],
                       const int nodes[.count], int status[.count], 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.  If pid is 0, then move_pages() moves  pages
       of the calling process.

       To move pages in another process requires the following privileges:

       •  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.   Preinitialization  of  the array to a value which cannot
       represent a real numa node or valid error of status array could help to identify  pages  that  have  been
       migrated.

       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.  If
       positive value is returned, it is the number of nonmigrated pages.

ERRORS

       Positive value
              The number of nonmigrated pages if they were the result of nonfatal reasons (since Linux 4.17).

       E2BIG  Too many pages to move.  Since Linux 2.6.29, the kernel no longer generates this error.

       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.

       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.

STANDARDS

       Linux.

HISTORY

       Linux 2.6.18.

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)