.\" Copyright 2003,2004 Andi Kleen, SuSE Labs. .\" and Copyright 2007 Lee Schermerhorn, Hewlett Packard .\" .\" %%%LICENSE_START(VERBATIM_PROF) .\" Permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" Permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" Since the Linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. The author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. .\" .\" Formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%LICENSE_END .\" .\" 2006-02-03, mtk, substantial wording changes and other improvements .\" 2007-08-27, Lee Schermerhorn .\" more precise specification of behavior. .\" .\" FIXME .\" Linux 3.8 added MPOL_MF_LAZY, which needs to be documented. .\" Does it also apply for move_pages()? .\" .\" commit b24f53a0bea38b266d219ee651b22dba727c44ae .\" Author: Lee Schermerhorn .\" Date: Thu Oct 25 14:16:32 2012 +0200 .\" .TH MBIND 2 2020-06-09 Linux "Linux Programmer's Manual" .SH NAME mbind \- set memory policy for a memory range .SH SYNOPSIS .nf .B "#include " .PP .BI "long mbind(void *" addr ", unsigned long " len ", int " mode , .BI " const unsigned long *" nodemask ", unsigned long " maxnode , .BI " unsigned " flags ); .PP Link with \fI\-lnuma\fP. .fi .SH DESCRIPTION .BR mbind () sets the NUMA memory policy, which consists of a policy mode and zero or more nodes, for the memory range starting with .I addr and continuing for .I len bytes. The memory policy defines from which node memory is allocated. .PP If the memory range specified by the .IR addr " and " len arguments includes an "anonymous" region of memory\(emthat is a region of memory created using the .BR mmap (2) system call with the .BR MAP_ANONYMOUS \(emor a memory-mapped file, mapped using the .BR mmap (2) system call with the .B MAP_PRIVATE flag, pages will be allocated only according to the specified policy when the application writes (stores) to the page. For anonymous regions, an initial read access will use a shared page in the kernel containing all zeros. For a file mapped with .BR MAP_PRIVATE , an initial read access will allocate pages according to the memory policy of the thread that causes the page to be allocated. This may not be the thread that called .BR mbind (). .PP The specified policy will be ignored for any .B MAP_SHARED mappings in the specified memory range. Rather the pages will be allocated according to the memory policy of the thread that caused the page to be allocated. Again, this may not be the thread that called .BR mbind (). .PP If the specified memory range includes a shared memory region created using the .BR shmget (2) system call and attached using the .BR shmat (2) system call, pages allocated for the anonymous or shared memory region will be allocated according to the policy specified, regardless of which process attached to the shared memory segment causes the allocation. If, however, the shared memory region was created with the .B SHM_HUGETLB flag, the huge pages will be allocated according to the policy specified only if the page allocation is caused by the process that calls .BR mbind () for that region. .PP By default, .BR mbind () has an effect only for new allocations; if the pages inside the range have been already touched before setting the policy, then the policy has no effect. This default behavior may be overridden by the .B MPOL_MF_MOVE and .B MPOL_MF_MOVE_ALL flags described below. .PP The .I mode argument must specify one of .BR MPOL_DEFAULT , .BR MPOL_BIND , .BR MPOL_INTERLEAVE , .BR MPOL_PREFERRED , or .BR MPOL_LOCAL (which are described in detail below). All policy modes except .B MPOL_DEFAULT require the caller to specify the node or nodes to which the mode applies, via the .I nodemask argument. .PP The .I mode argument may also include an optional .IR "mode flag" . The supported .I "mode flags" are: .TP .BR MPOL_F_STATIC_NODES " (since Linux-2.6.26)" A nonempty .I nodemask specifies physical node IDs. Linux does not remap the .I nodemask when the thread moves to a different cpuset context, nor when the set of nodes allowed by the thread's current cpuset context changes. .TP .BR MPOL_F_RELATIVE_NODES " (since Linux-2.6.26)" A nonempty .I nodemask specifies node IDs that are relative to the set of node IDs allowed by the thread's current cpuset. .PP .I nodemask points to a bit mask of nodes containing up to .I maxnode bits. The bit mask size is rounded to the next multiple of .IR "sizeof(unsigned long)" , but the kernel will use bits only up to .IR maxnode . A NULL value of .I nodemask or a .I maxnode value of zero specifies the empty set of nodes. If the value of .I maxnode is zero, the .I nodemask argument is ignored. Where a .I nodemask is required, it must contain at least one node that is on-line, allowed by the thread's current cpuset context (unless the .B MPOL_F_STATIC_NODES mode flag is specified), and contains memory. .PP The .I mode argument must include one of the following values: .TP .B MPOL_DEFAULT This mode requests that any nondefault policy be removed, restoring default behavior. When applied to a range of memory via .BR mbind (), this means to use the thread memory policy, which may have been set with .BR set_mempolicy (2). If the mode of the thread memory policy is also .BR MPOL_DEFAULT , the system-wide default policy will be used. The system-wide default policy allocates pages on the node of the CPU that triggers the allocation. For .BR MPOL_DEFAULT , the .I nodemask and .I maxnode arguments must be specify the empty set of nodes. .TP .B MPOL_BIND This mode specifies a strict policy that restricts memory allocation to the nodes specified in .IR nodemask . If .I nodemask specifies more than one node, page allocations will come from the node with sufficient free memory that is closest to the node where the allocation takes place. Pages will not be allocated from any node not specified in the IR nodemask . (Before Linux 2.6.26, .\" commit 19770b32609b6bf97a3dece2529089494cbfc549 page allocations came from the node with the lowest numeric node ID first, until that node contained no free memory. Allocations then came from the node with the next highest node ID specified in .I nodemask and so forth, until none of the specified nodes contained free memory.) .TP .B MPOL_INTERLEAVE This mode specifies that page allocations be interleaved across the set of nodes specified in .IR nodemask . This optimizes for bandwidth instead of latency by spreading out pages and memory accesses to those pages across multiple nodes. To be effective the memory area should be fairly large, at least 1\ MB or bigger with a fairly uniform access pattern. Accesses to a single page of the area will still be limited to the memory bandwidth of a single node. .TP .B MPOL_PREFERRED This mode sets the preferred node for allocation. The kernel will try to allocate pages from this node first and fall back to other nodes if the preferred nodes is low on free memory. If .I nodemask specifies more than one node ID, the first node in the mask will be selected as the preferred node. If the .I nodemask and .I maxnode arguments specify the empty set, then the memory is allocated on the node of the CPU that triggered the allocation. .TP .BR MPOL_LOCAL " (since Linux 3.8)" .\" commit 479e2802d09f1e18a97262c4c6f8f17ae5884bd8 .\" commit f2a07f40dbc603c15f8b06e6ec7f768af67b424f This mode specifies "local allocation"; the memory is allocated on the node of the CPU that triggered the allocation (the "local node"). The .I nodemask and .I maxnode arguments must specify the empty set. If the "local node" is low on free memory, the kernel will try to allocate memory from other nodes. The kernel will allocate memory from the "local node" whenever memory for this node is available. If the "local node" is not allowed by the thread's current cpuset context, the kernel will try to allocate memory from other nodes. The kernel will allocate memory from the "local node" whenever it becomes allowed by the thread's current cpuset context. By contrast, .B MPOL_DEFAULT reverts to the memory policy of the thread (which may be set via .BR set_mempolicy (2)); that policy may be something other than "local allocation". .PP If .B MPOL_MF_STRICT is passed in .I flags and .I mode is not .BR MPOL_DEFAULT , then the call fails with the error .B EIO if the existing pages in the memory range don't follow the policy. .\" According to the kernel code, the following is not true .\" --Lee Schermerhorn .\" In 2.6.16 or later the kernel will also try to move pages .\" to the requested node with this flag. .PP If .B MPOL_MF_MOVE is specified in .IR flags , then the kernel will attempt to move all the existing pages in the memory range so that they follow the policy. Pages that are shared with other processes will not be moved. If .B MPOL_MF_STRICT is also specified, then the call fails with the error .B EIO if some pages could not be moved. .PP If .B MPOL_MF_MOVE_ALL is passed in .IR flags , then the kernel will attempt to move all existing pages in the memory range regardless of whether other processes use the pages. The calling thread must be privileged .RB ( CAP_SYS_NICE ) to use this flag. If .B MPOL_MF_STRICT is also specified, then the call fails with the error .B EIO if some pages could not be moved. .\" --------------------------------------------------------------- .SH RETURN VALUE On success, .BR mbind () returns 0; on error, \-1 is returned and .I errno is set to indicate the error. .\" --------------------------------------------------------------- .SH ERRORS .\" I think I got all of the error returns. --Lee Schermerhorn .TP .B EFAULT Part or all of the memory range specified by .I nodemask and .I maxnode points outside your accessible address space. Or, there was an unmapped hole in the specified memory range specified by .IR addr and .IR len . .TP .B EINVAL An invalid value was specified for .I flags or .IR mode ; or .I addr + len was less than .IR addr ; or .I addr is not a multiple of the system page size. Or, .I mode is .B MPOL_DEFAULT and .I nodemask specified a nonempty set; or .I mode is .B MPOL_BIND or .B MPOL_INTERLEAVE and .I nodemask is empty. Or, .I maxnode exceeds a kernel-imposed limit. .\" As at 2.6.23, this limit is "a page worth of bits", e.g., .\" 8 * 4096 bits, assuming a 4kB page size. Or, .I nodemask specifies one or more node IDs that are greater than the maximum supported node ID. Or, none of the node IDs specified by .I nodemask are on-line and allowed by the thread's current cpuset context, or none of the specified nodes contain memory. Or, the .I mode argument specified both .B MPOL_F_STATIC_NODES and .BR MPOL_F_RELATIVE_NODES . .TP .B EIO .B MPOL_MF_STRICT was specified and an existing page was already on a node that does not follow the policy; or .B MPOL_MF_MOVE or .B MPOL_MF_MOVE_ALL was specified and the kernel was unable to move all existing pages in the range. .TP .B ENOMEM Insufficient kernel memory was available. .TP .B EPERM The .I flags argument included the .B MPOL_MF_MOVE_ALL flag and the caller does not have the .B CAP_SYS_NICE privilege. .\" --------------------------------------------------------------- .SH VERSIONS The .BR mbind () system call was added to the Linux kernel in version 2.6.7. .SH CONFORMING TO This system call is Linux-specific. .SH NOTES For information on library support, see .BR numa (7). .PP NUMA policy is not supported on a memory-mapped file range that was mapped with the .B MAP_SHARED flag. .PP The .B MPOL_DEFAULT mode can have different effects for .BR mbind () and .BR set_mempolicy (2). When .B MPOL_DEFAULT is specified for .BR set_mempolicy (2), the thread's memory policy reverts to the system default policy or local allocation. When .B MPOL_DEFAULT is specified for a range of memory using .BR mbind (), any pages subsequently allocated for that range will use the thread's memory policy, as set by .BR set_mempolicy (2). This effectively removes the explicit policy from the specified range, "falling back" to a possibly nondefault policy. To select explicit "local allocation" for a memory range, specify a .I mode of .B MPOL_LOCAL or .B MPOL_PREFERRED with an empty set of nodes. This method will work for .BR set_mempolicy (2), as well. .PP Support for huge page policy was added with 2.6.16. For interleave policy to be effective on huge page mappings the policied memory needs to be tens of megabytes or larger. .PP Before Linux 5.7. .\" commit dcf1763546d76c372f3136c8d6b2b6e77f140cf0 .B MPOL_MF_STRICT was ignored on huge page mappings. .PP .B MPOL_MF_MOVE and .B MPOL_MF_MOVE_ALL are available only on Linux 2.6.16 and later. .SH SEE ALSO .BR get_mempolicy (2), .BR getcpu (2), .BR mmap (2), .BR set_mempolicy (2), .BR shmat (2), .BR shmget (2), .BR numa (3), .BR cpuset (7), .BR numa (7), .BR numactl (8) .SH COLOPHON This page is part of release 5.10 of the Linux .I man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/.