diff --git a/man2/set_mempolicy.2 b/man2/set_mempolicy.2 index 1022783c9..1a82c1f0b 100644 --- a/man2/set_mempolicy.2 +++ b/man2/set_mempolicy.2 @@ -1,4 +1,5 @@ .\" Copyright 2003,2004 Andi Kleen, SuSE Labs. +.\" and Copyright 2007 Lee Schermerhorn, Hewlett Packard .\" .\" Permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are @@ -18,88 +19,150 @@ .\" the source, must acknowledge the copyright and authors of this work. .\" .\" 2006-02-03, mtk, substantial wording changes and other improvements +.\" 2007-06-01, lts, more precise specification of behavior. .\" -.TH SET_MEMPOLICY 2 2006-02-07 "Linux" "Linux Programmer's Manual" +.TH SET_MEMPOLICY 2 2006-02-07 Linux "Linux Programmer's Manual" .SH NAME -set_mempolicy \- set default NUMA memory policy for a process and its children. +set_mempolicy \- set default NUMA memory policy for a process and its children .SH SYNOPSIS .nf .B "#include " .sp -.BI "int set_mempolicy(int " policy ", unsigned long *" nodemask , +.BI "int set_mempolicy(int " mode ", unsigned long *" nodemask , .BI " unsigned long " maxnode ); +.sp +.BI "cc ... \-lnuma" .fi .SH DESCRIPTION .BR set_mempolicy () -sets the NUMA memory policy of the calling process to -.IR policy . +sets the NUMA memory policy of the calling process, +which consists of a policy mode and zero or more nodes, +to the values specified by the +.IR mode , +.I nodemask +and +.IR maxnode +arguments. A NUMA machine has different memory controllers with different distances to specific CPUs. -The memory policy defines in which node memory is allocated for +The memory policy defines from which node memory is allocated for the process. -This system call defines the default policy for the process; -in addition a policy can be set for specific memory ranges using +This system call defines the default policy for the process. +The process policy governs allocation of pages in the process' +address space outside of memory ranges +controlled by a more specific policy set by .BR mbind (2). +The process default policy also controls allocation of any pages for +memory mapped files mapped using the +.BR mmap (2) +call with the +.B MAP_PRIVATE +flag and that are only read [loaded] from by the task +and of memory mapped files mapped using the +.BR mmap (2) +call with the +.B MAP_SHARED +flag, regardless of the access type. The policy is only applied when a new page is allocated for the process. For anonymous memory this is when the page is first touched by the application. -Available policies are +The +.I mode +argument must specify one of .BR MPOL_DEFAULT , .BR MPOL_BIND , -.BR MPOL_INTERLEAVE , +.B MPOL_INTERLEAVE +or .BR MPOL_PREFERRED . -All policies except +All modes except .B MPOL_DEFAULT -require the caller to specify the nodes to which the policy applies in the +require the caller to specify via the .I nodemask -parameter. +parameter +one or more nodes. + .I nodemask -is pointer to a bit field of nodes that contains up to +points to a bit mask of node ids that contains up to .I maxnode bits. -The bit field size is rounded to the next multiple of +The bit mask size is rounded to the next multiple of .IR "sizeof(unsigned long)" , but the kernel will only use bits 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. The .B MPOL_DEFAULT -policy is the default and means to allocate memory locally, +mode is the default and means to allocate memory locally, i.e., on the node of the CPU that triggered the allocation. .I nodemask -should be specified as NULL. +must be specified as NULL. +If the "local node" contains no free memory, the system will +attempt to allocate memory from a "near by" node. The .B MPOL_BIND -policy is a strict policy that restricts memory allocation to the +mode defines a strict policy that restricts memory allocation to the nodes specified in .IR nodemask . -There won't be allocations on other nodes. +If +.I nodemask +specifies more than one node, page allocations will come from +the node with the lowest numeric node id first, until that node +contains no free memory. +Allocations will then come from the node with the next highest +node id specified in +.I nodemask +and so forth, until none of the specified nodes contain free memory. +Pages will not be allocated from any node not specified in the +.IR nodemask . .B MPOL_INTERLEAVE -interleaves allocations to the nodes specified in -.IR nodemask . -This optimizes for bandwidth instead of latency. -To be effective the memory area should be fairly large, -at least 1MB or bigger. +interleaves page allocations across the nodes specified in +.I nodemask +in numeric node id order. +This optimizes for bandwidth instead of latency +by spreading out pages and memory accesses to those pages across +multiple nodes. +However, accesses to a single page will still be limited to +the memory bandwidth of a single node. +.\" NOTE: the following sentence doesn't make sense in the context +.\" of set_mempolicy() -- no memory area specified. +.\" To be effective the memory area should be fairly large, +.\" at least 1MB or bigger. .B MPOL_PREFERRED sets the preferred node for allocation. -The kernel will try to allocate in this -node first and fall back to other nodes if the preferred node is low on free +The kernel will try to allocate pages from this node first +and fall back to "near by" nodes if the preferred node is low on free memory. -Only the first node in the +If .I nodemask -is used. -If no node is set in the mask, then the memory is allocated on +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 (like .BR MPOL_DEFAULT ). -The memory policy is preserved across an +The process memory policy is preserved across an .BR execve (2), and is inherited by child processes created using .BR fork (2) @@ -112,21 +175,62 @@ returns 0; on error, \-1 is returned and .I errno is set to indicate the error. -.\" .SH ERRORS -.\" FIXME no errors are listed on this page -.\" . -.\" .TP -.\" .B EINVAL -.\" .I mode is invalid. +.SH ERRORS +.TP +.B EINVAL +.I mode is invalid. +Or, +.I mode +is +.I MPOL_DEFAULT +and +.I nodemask +is non-empty, +or +.I mode +is +.I MPOL_BIND +or +.I MPOL_INTERLEAVE +and +.I nodemask +is empty. +Or, +.I maxnode +specifies more than a page worth of bits. +Or, +.I nodemask +specifies one or more node ids that are +greater than the maximum supported node id, +or are not allowed in the calling task's context. +.\" "calling task's context" refers to cpusets. No man page avail to ref. --lts +Or, none of the node ids specified by +.I nodemask +are on-line, or none of the specified nodes contain memory. +.TP +.B EFAULT +Part of all of the memory range specified by +.I nodemask +and +.I maxnode +points outside your accessible address space. +.TP +.B ENOMEM +Insufficient kernel memory was available. + .SH CONFORMING TO This system call is Linux specific. .SH NOTES Process policy is not remembered if the page is swapped out. +When such a page is paged back in, it will use the policy of +the process or memory range that is in effect at the time the +page is allocated. .SS "Versions and Library Support" See .BR mbind (2). .SH SEE ALSO .BR mbind (2), +.BR mmap (2), .BR get_mempolicy (2), .BR numactl (8), .BR numa (3)