.\" SPDX-License-Identifier: Linux-man-pages-copyleft-2-para .\" .\" This manpage is Copyright (C) 2006 Silicon Graphics, Inc. .\" Christoph Lameter .\" .\" FIXME Should programs normally be using move_pages() directly, or should .\" they rather be using interfaces in the numactl package? .\" (e.g., compare with recommendation in mbind(2)). .\" Does this page need to give advice on this topic? .\" .TH move_pages 2 2023-07-15 "Linux man-pages 6.05.01" .SH NAME move_pages \- move individual pages of a process to another node .SH LIBRARY NUMA (Non-Uniform Memory Access) policy library .RI ( libnuma ", " \-lnuma ) .SH SYNOPSIS .nf .B #include .PP .BI "long move_pages(int " pid ", unsigned long " count ", \ void *" pages [. count ], .BI " const int " nodes [. count "], int " status [. count "], \ int " flags ); .fi .SH DESCRIPTION .BR move_pages () moves the specified .I pages of the process .I pid to the memory nodes specified by .IR nodes . The result of the move is reflected in .IR status . The .I flags indicate constraints on the pages to be moved. .PP .I pid is the ID of the process in which pages are to be moved. If .I pid is 0, then .BR move_pages () moves pages of the calling process. .PP To move pages in another process requires the following privileges: .IP \[bu] 3 Up to and including Linux 4.12: the caller must be privileged .RB ( 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. .IP \[bu] 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, .\" commit 197e7e521384a23b9e585178f3f11c9fa08274b9 permission is governed by a ptrace access mode .B PTRACE_MODE_READ_REALCREDS check with respect to the target process; see .BR ptrace (2). .PP .I count is the number of pages to move. It defines the size of the three arrays .IR pages , .IR nodes , and .IR status . .PP .I pages is an array of pointers to the pages that should be moved. These are pointers that should be aligned to page boundaries. .\" FIXME Describe the result if pointers in the 'pages' array are .\" not aligned to page boundaries Addresses are specified as seen by the process specified by .IR pid . .PP .I nodes is an array of integers that specify the desired location for each page. Each element in the array is a node number. .I nodes can also be NULL, in which case .BR move_pages () does not move any pages but instead will return the node where each page currently resides, in the .I status array. Obtaining the status of each page may be necessary to determine pages that need to be moved. .PP .I status is an array of integers that return the status of each page. The array contains valid values only if .BR 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. .PP .I flags specify what types of pages to move. .B MPOL_MF_MOVE means that only pages that are in exclusive use by the process are to be moved. .B MPOL_MF_MOVE_ALL means that pages shared between multiple processes can also be moved. The process must be privileged .RB ( CAP_SYS_NICE ) to use .BR MPOL_MF_MOVE_ALL . .SS Page states in the status array The following values can be returned in each element of the .I status array. .TP .B 0..MAX_NUMNODES Identifies the node on which the page resides. .TP .B \-EACCES The page is mapped by multiple processes and can be moved only if .B MPOL_MF_MOVE_ALL is specified. .TP .B \-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. .TP .B \-EFAULT This is a zero page or the memory area is not mapped by the process. .TP .B \-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. .TP .B \-EINVAL A dirty page cannot be moved. The filesystem does not provide a migration function and has no ability to write back pages. .TP .B \-ENOENT The page is not present. .TP .B \-ENOMEM Unable to allocate memory on target node. .SH RETURN VALUE On success .BR move_pages () returns zero. .\" FIXME . Is the following quite true: does the wrapper in numactl .\" do the right thing? On error, it returns \-1, and sets .I errno to indicate the error. If positive value is returned, it is the number of nonmigrated pages. .SH ERRORS .TP .B Positive value The number of nonmigrated pages if they were the result of nonfatal reasons (since .\" commit a49bd4d7163707de377aee062f17befef6da891b Linux 4.17). .TP .B E2BIG Too many pages to move. Since Linux 2.6.29, .\" commit 3140a2273009c01c27d316f35ab76a37e105fdd8 the kernel no longer generates this error. .TP .B EACCES .\" FIXME Clarify "current cpuset" in the description of the EACCES error. .\" Is that the cpuset of the caller or the target? One of the target nodes is not allowed by the current cpuset. .TP .B EFAULT Parameter array could not be accessed. .TP .B EINVAL Flags other than .B MPOL_MF_MOVE and .B MPOL_MF_MOVE_ALL was specified or an attempt was made to migrate pages of a kernel thread. .TP .B ENODEV One of the target nodes is not online. .TP .B EPERM The caller specified .B MPOL_MF_MOVE_ALL without sufficient privileges .RB ( 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 .RB ( CAP_SYS_NICE ). .TP .B ESRCH Process does not exist. .SH STANDARDS Linux. .SH HISTORY Linux 2.6.18. .SH NOTES For information on library support, see .BR numa (7). .PP Use .BR get_mempolicy (2) with the .B MPOL_F_MEMS_ALLOWED flag to obtain the set of nodes that are allowed by .\" FIXME Clarify "current cpuset". Is that the cpuset of the caller .\" or the target? the current cpuset. Note that this information is subject to change at any time by manual or automatic reconfiguration of the cpuset. .PP Use of this function may result in pages whose location (node) violates the memory policy established for the specified addresses (See .BR mbind (2)) and/or the specified process (See .BR set_mempolicy (2)). That is, memory policy does not constrain the destination nodes used by .BR move_pages (). .PP The .I header is not included with glibc, but requires installing .I libnuma\-devel or a similar package. .SH SEE ALSO .BR get_mempolicy (2), .BR mbind (2), .BR set_mempolicy (2), .BR numa (3), .BR numa_maps (5), .BR cpuset (7), .BR numa (7), .BR migratepages (8), .BR numastat (8)