# move_pages

## 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.
    


## 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.
    


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