Section (2) move_pages
move_pages — move individual pages of a process to another node
|unsigned long count,|
|const int *nodes,|
move_pages() moves the
the memory nodes specified by
nodes. The result of the move
is reflected in
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
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).
count is the
number of pages to move. It defines the size of the three
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
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
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
Page states in the status array
The following values can be returned in each element of
Identifies the node on which the page resides.
The page is mapped by multiple processes and can be moved only if
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.
returns zero. On error, it returns −1, and sets
errno to indicate the error.
Too many pages to move. Since Linux 2.6.29, the kernel no longer generates this error.
One of the target nodes is not allowed by the current cpuset.
Parameter array could not be accessed.
Flags other than
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 (
Process does not exist.
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
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
header is not included with glibc, but requires installing
libnuma-devel or a
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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?