Manpage of MOVE_PAGES
MOVE_PAGESSection: Linux Programmer's Manual (2)
NAMEmove_pages - move individual pages of a process to another node
#include <numaif.h>long move_pages(int pid, unsigned long count, void **pages, const int *nodes, int *status, int flags);
DESCRIPTIONmove_pages() moves the specified pagesof the process pidto the memory nodes specified by nodes. The result of the move is reflected in status. The flagsindicate constraints on the pages to be moved.
pidis the ID of the process in which pages are to be moved. If pidis 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_REALCREDScheck with respect to the target process; see ptrace(2).
countis the number of pages to move. It defines the size of the three arrays pages, nodes, and status.
pagesis 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.
nodesis an array of integers that specify the desired location for each page. Each element in the array is a node number. nodescan 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 statusarray. Obtaining the status of each page may be necessary to determine pages that need to be moved.
statusis 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.
flagsspecify what types of pages to move. MPOL_MF_MOVEmeans that only pages that are in exclusive use by the process are to be moved. MPOL_MF_MOVE_ALLmeans 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 arrayThe following values can be returned in each element of the statusarray.
- Identifies the node on which the page resides.
- The page is mapped by multiple processes and can be moved only if MPOL_MF_MOVE_ALLis specified.
- 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.
- This is a zero page or the memory area is not mapped by the process.
- 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.
- A dirty page cannot be moved. The filesystem does not provide a migration function and has no ability to write back pages.
- The page is not present.
- Unable to allocate memory on target node.
RETURN VALUEOn success move_pages() returns zero. On error, it returns -1, and sets errnoto indicate the error.
- Too many pages to move.
- One of the target nodes is not allowed by the current cpuset.
- Parameter array could not be accessed.
- Flags other than MPOL_MF_MOVEand MPOL_MF_MOVE_ALLwas specified or an attempt was made to migrate pages of a kernel thread.
- One of the target nodes is not online.
- 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.
- The caller specified MPOL_MF_MOVE_ALLwithout 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).
- Process does not exist.
VERSIONSmove_pages() first appeared on Linux in version 2.6.18.
CONFORMING TOThis system call is Linux-specific.
NOTESFor information on library support, see numa(7).
Use get_mempolicy(2) with the MPOL_F_MEMS_ALLOWEDflag 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-develor a similar package.
SEE ALSOget_mempolicy(2), mbind(2), set_mempolicy(2), numa(3), numa_maps(5), cpuset(7), numa(7), migratepages(8), numastat(8)
- RETURN VALUE
- CONFORMING TO
- SEE ALSO
This document was created by man2html, using the manual pages.
Time: 19:53:40 GMT, October 26, 2017 Click Here!