mirror of https://github.com/mkerrisk/man-pages
+ changed the "policy" parameter to "mode" through out the
descriptions in an attempt to promote the concept that the memory
policy is a tuple consisting of a mode and optional set of nodes.
+ rewrite portions of description for clarification.
++ clarify interaction of policy with mmap()'d files and shared
memory regions, including SHM_HUGE regions.
++ defined how "empty set of nodes" specified and what this
means for MPOL_PREFERRED.
++ mention what happens if local/target node contains no
free memory.
++ clarify semantics of multiple nodes to BIND policy.
Note: subject to change. We'll fix the man pages when/if
this happens.
+ added all errors currently returned by sys call.
+ added mmap(2), shmget(2), shmat(2) to See Also list.
This commit is contained in:
Michael Kerrisk
parent
03d2434e5c
commit
9f5682a8ed
344
man2/mbind.2
344
man2/mbind.2
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@ -18,15 +18,17 @@
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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.\" 2006-02-03, mtk, substantial wording changes and other improvements
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.\" 2007-08-27, Lee Schermerhorn <Lee.Schermerhorn@hp.com>
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.\" more precise specification of behavior.
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.\"
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.TH MBIND 2 2006-02-07 "Linux" "Linux Programmer's Manual"
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.TH MBIND 2 "2007-06-01" "SuSE Labs" "Linux Programmer's Manual"
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.SH NAME
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mbind \- Set memory policy for a memory range
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.SH SYNOPSIS
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.nf
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.B "#include <numaif.h>"
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.sp
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.BI "int mbind(void *" start ", unsigned long " len ", int " policy ,
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.BI "int mbind(void *" start ", unsigned long " len ", int " mode ,
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.BI " unsigned long *" nodemask ", unsigned long " maxnode ,
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.BI " unsigned " flags );
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.sp
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@ -34,76 +36,178 @@ mbind \- Set memory policy for a memory range
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.fi
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.SH DESCRIPTION
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.BR mbind ()
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sets the NUMA memory
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.I policy
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sets the NUMA memory policy,
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which consists of a policy mode and zero or more nodes,
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for the memory range starting with
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.I start
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and continuing for
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.IR len
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bytes.
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The memory of a NUMA machine is divided into multiple nodes.
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The memory policy defines in which node memory is allocated.
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The memory policy defines from which node memory is allocated.
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If the memory range specified by the
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.IR start " and " len
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arguments includes an "anonymous" region of memory\(emthat is
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a region of memory created using the
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.BR mmap (2)
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system call with the
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.BR MAP_ANONYMOUS \(emor
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a memory mapped file, mapped using the
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.BR mmap (2)
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system call with the
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.B MAP_PRIVATE
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flag, pages will only be allocated according to the specified
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policy when the application writes [stores] to the page.
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For anonymous regions, an initial read access will use a shared
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page in the kernel containing all zeros.
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For a file mapped with
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.BR MAP_PRIVATE ,
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an initial read access will allocate pages according to the
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process policy of the process that causes the page to be allocated.
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This may not be the process that called
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.BR mbind ().
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The specified policy will be ignored for any
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.B MAP_SHARED
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mappings in the specified memory range.
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Rather the pages will be allocated according to the process policy
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of the process that caused the page to be allocated.
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Again, this may not be the process that called
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.BR mbind ().
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If the specified memory range includes a shared memory region
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created using the
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.BR shmget (2)
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system call and attached using the
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.BR shmat (2)
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system call,
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pages allocated for the anonymous or shared memory region will
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be allocated according to the policy specified, regardless which
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process attached to the shared memory segment causes the allocation.
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If, however, the shared memory region was created with the
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.B SHM_HUGETLB
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flag,
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the huge pages will be allocated according to the policy specified
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only if the page allocation is caused by the task that calls
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.BR mbind ()
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for that region.
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By default,
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.BR mbind ()
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only has an effect for new allocations; if the pages inside
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the range have been already touched before setting the policy,
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then the policy has no effect.
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This default behavior may be overridden by the
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.BR MPOL_MF_MOVE
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and
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.B MPOL_MF_MOVE_ALL
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flags described below.
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Available policies are
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The
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.I mode
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argument must specify one of
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.BR MPOL_DEFAULT ,
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.BR MPOL_BIND ,
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.BR MPOL_INTERLEAVE ,
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and
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.B MPOL_INTERLEAVE
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or
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.BR MPOL_PREFERRED .
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All policies except
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All policy modes except
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.B MPOL_DEFAULT
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require the caller to specify the nodes to which the policy applies in the
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require the caller to specify via the
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.I nodemask
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parameter.
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parameter,
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the node or nodes to which the mode applies.
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.I nodemask
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is a bit mask of nodes containing up to
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points to a bitmask of nodes containing up to
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.I maxnode
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bits.
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The actual number of bytes transferred via this argument
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is rounded up to the next multiple of
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The bit mask size is rounded to the next multiple of
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.IR "sizeof(unsigned long)" ,
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but the kernel will only use bits up to
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.IR maxnode .
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A NULL argument means an empty set of nodes.
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A NULL value of
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.I nodemask
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or a
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.I maxnode
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value of zero specifies the empty set of nodes.
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If the value of
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.I maxnode
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is zero,
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the
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.I nodemask
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argument is ignored.
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The
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.B MPOL_DEFAULT
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policy is the default and means to use the underlying process policy
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(which can be modified with
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.BR set_mempolicy (2)).
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Unless the process policy has been changed this means to allocate
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memory on the node of the CPU that triggered the allocation.
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mode specifies that the default policy be used.
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When applied to a range of memory via
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.IR mbind (),
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this means to use the process policy,
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which may have been set with
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.BR set_mempolicy (2).
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If the mode of the process policy is also
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.BR MPOL_DEFAULT ,
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the system-wide default policy will be used.
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The system-wide default policy will allocate
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pages on the node of the CPU that triggers the allocation.
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For
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.BR MPOL_DEFAULT ,
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the
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.I nodemask
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should be specified as NULL.
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and
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.I maxnode
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arguments must be specify the empty set of nodes.
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The
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.B MPOL_BIND
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policy is a strict policy that restricts memory allocation to the
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nodes specified in
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mode specifies a strict policy that restricts memory allocation to
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the nodes specified in
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.IR nodemask .
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If
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.I nodemask
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specifies more than one node, page allocations will come from
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the node with the lowest numeric node id first, until that node
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contains no free memory.
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Allocations will then come from the node with the next highest
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node id specified in
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.I nodemask
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and so forth, until none of the specified nodes contain free memory.
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Pages will not be allocated from any node not specified in the
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.IR nodemask .
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There won't be allocations on other nodes.
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The
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.B MPOL_INTERLEAVE
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interleaves allocations to the nodes specified in
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mode specifies that page allocations be interleaved across the
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set of nodes specified in
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.IR nodemask .
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This optimizes for bandwidth instead of latency.
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This optimizes for bandwidth instead of latency
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by spreading out pages and memory accesses to those pages across
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multiple nodes.
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To be effective the memory area should be fairly large,
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at least 1MB or bigger.
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at least 1MB or bigger with a fairly uniform access pattern.
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Accesses to a single page of the area will still be limited to
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the memory bandwidth of a single node.
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.B MPOL_PREFERRED
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sets the preferred node for allocation.
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The kernel will try to allocate in this
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The kernel will try to allocate pages from this
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node first and fall back to other nodes if the
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preferred nodes is low on free memory.
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Only the first node in the
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If
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.I nodemask
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is used.
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If no node is set in the mask, then the memory is allocated on
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the node of the CPU that triggered the allocation allocation).
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specifies more than one node id, the first node in the
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mask will be selected as the preferred node.
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If the
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.I nodemask
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and
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.I maxnode
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arguments specify the empty set, then the memory is allocated on
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the node of the CPU that triggered the allocation.
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This is the only way to specify "local allocation" for a
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range of memory via
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.IR mbind (2).
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If
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.B MPOL_MF_STRICT
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@ -115,17 +219,18 @@ is not
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.BR MPOL_DEFAULT ,
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then the call will fail with the error
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.B EIO
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if the existing pages in the mapping don't follow the policy.
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In 2.6.16 or later the kernel will also try to move pages
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to the requested node with this flag.
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if the existing pages in the memory range don't follow the policy.
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.\" According to the kernel code, the following is not true --lts
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.\" In 2.6.16 or later the kernel will also try to move pages
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.\" to the requested node with this flag.
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If
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.B MPOL_MF_MOVE
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is passed in
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is specified in
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.IR flags ,
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then an attempt will be made to
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move all the pages in the mapping so that they follow the policy.
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Pages that are shared with other processes are not moved.
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then the kernel will attempt to move all the existing pages
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in the memory range so that they follow the policy.
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Pages that are shared with other processes will not be moved.
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If
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.B MPOL_MF_STRICT
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is also specified, then the call will fail with the error
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@ -136,8 +241,8 @@ If
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.B MPOL_MF_MOVE_ALL
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is passed in
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.IR flags ,
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then all pages in the mapping will be moved regardless of whether
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other processes use the pages.
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then the kernel will attempt to move all existing pages in the memory range
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regardless of whether other processes use the pages.
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The calling process must be privileged
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.RB ( CAP_SYS_NICE )
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to use this flag.
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@ -146,6 +251,7 @@ If
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is also specified, then the call will fail with the error
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.B EIO
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if some pages could not be moved.
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.\" ---------------------------------------------------------------
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.SH RETURN VALUE
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On success,
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.BR mbind ()
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@ -153,11 +259,9 @@ returns 0;
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on error, \-1 is returned and
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.I errno
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is set to indicate the error.
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.\" ---------------------------------------------------------------
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.SH ERRORS
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.TP
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.B EFAULT
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There was a unmapped hole in the specified memory range
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or a passed pointer was not valid.
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.\" I think I got all of the error returns. --lts
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.TP
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.B EINVAL
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An invalid value was specified for
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@ -169,55 +273,102 @@ or
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was less than
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.IR start ;
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or
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.I policy
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was
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.B MPOL_DEFAULT
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.I start
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is not a multiple of the system page size.
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Or,
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.I mode
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is
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.I MPOL_DEFAULT
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and
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.I nodemask
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pointed to a non-empty set;
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specified a non-empty set;
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or
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.I policy
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was
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.B MPOL_BIND
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.I mode
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is
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.I MPOL_BIND
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or
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.B MPOL_INTERLEAVE
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.I MPOL_INTERLEAVE
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and
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.I nodemask
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pointed to an empty set,
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is empty.
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Or,
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.I maxnode
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specifies more than a page worth of bits.
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Or,
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.I nodemask
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specifies one or more node ids that are
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greater than the maximum supported node id,
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or are not allowed in the calling task's context.
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.\" "calling task's context" refers to cpusets. No man page avail to ref. --lts
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Or, none of the node ids specified by
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.I nodemask
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are on-line, or none of the specified nodes contain memory.
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.TP
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.B EFAULT
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Part of all of the memory range specified by
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.I nodemask
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and
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.I maxnode
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points outside your accessible address space.
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Or, there was a unmapped hole in the specified memory range.
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.TP
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.B EIO
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.B MPOL_MF_STRICT
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was specified and an existing page was already on a node
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that does not follow the policy.
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that does not follow the policy;
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or
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.B MPOL_MF_MOVE
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or
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.B MPOL_MF_MOVE_ALL
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was specified and the kernel was unable to move all existing
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pages in the range.
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.TP
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.B ENOMEM
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System out of memory.
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.SH CONFORMING TO
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This system call is Linux specific.
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Insufficient kernel memory was available.
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.TP
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.B EPERM
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The
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.I flags
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argument included the
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.B MPOL_MF_MOVE_ALL
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flag and the caller does not have the
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.B CAP_SYS_NICE
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privilege.
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.\" ---------------------------------------------------------------
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.SH NOTES
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NUMA policy is not supported on file mappings.
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NUMA policy is not supported on a memory mapped file range
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that was mapped with the
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.I MAP_SHARED
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flag.
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.B MPOL_MF_STRICT
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is ignored on huge page mappings right now.
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is ignored on huge page mappings.
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It is unfortunate that the same flag,
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The
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.BR MPOL_DEFAULT ,
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has different effects for
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mode has different effects for
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.BR mbind (2)
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and
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.BR set_mempolicy (2).
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To select "allocation on the node of the CPU that
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triggered the allocation" (like
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.BR set_mempolicy (2)
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.BR MPOL_DEFAULT )
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when calling
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When
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.B MPOL_DEFAULT
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is specified for a range of memory using
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.BR mbind (),
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any pages subsequently allocated for that range will use
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the process' policy, as set by
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.BR set_mempolicy (2).
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||||
This effectively removes the explicit policy from the
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specified range.
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To select "local allocation" for a memory range,
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specify a
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.I policy
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.I mode
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of
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.B MPOL_PREFERRED
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with an empty
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.IR nodemask .
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with an empty set of nodes.
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This method will work for
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.BR set_mempolicy (2),
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as well.
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.\" ---------------------------------------------------------------
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.SS "Versions and Library Support"
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The
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.BR mbind (),
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@ -228,16 +379,18 @@ system calls were added to the Linux kernel with version 2.6.7.
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They are only available on kernels compiled with
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.BR CONFIG_NUMA .
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Support for huge page policy was added with 2.6.16.
|
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For interleave policy to be effective on huge page mappings the
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policied memory needs to be tens of megabytes or larger.
|
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You can link with
|
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.I -lnuma
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to get system call definitions.
|
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.I libnuma
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||||
and the required
|
||||
.I numaif.h
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||||
header.
|
||||
are available in the
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.I numactl
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package.
|
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.B MPOL_MF_MOVE
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and
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.B MPOL_MF_MOVE_ALL
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||||
are only available on Linux 2.6.16 and later.
|
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|
||||
These system calls should not be used directly.
|
||||
However, applications should not use these system calls directly.
|
||||
Instead, the higher level interface provided by the
|
||||
.BR numa (3)
|
||||
functions in the
|
||||
|
|
@ -247,20 +400,25 @@ The
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|||
.I numactl
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||||
package is available at
|
||||
.IR ftp://ftp.suse.com/pub/people/ak/numa/ .
|
||||
|
||||
You can link with
|
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.I \-lnuma
|
||||
to get system call definitions.
|
||||
.I libnuma
|
||||
is available in the
|
||||
.I numactl
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||||
The package is also included in some Linux distributions.
|
||||
Some distributions include the development library and header
|
||||
in the separate
|
||||
.I numactl-devel
|
||||
package.
|
||||
This package also has the
|
||||
.I numaif.h
|
||||
header.
|
||||
|
||||
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.
|
||||
|
||||
.B MPOL_MF_MOVE
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||||
and
|
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.B MPOL_MF_MOVE_ALL
|
||||
are only available on Linux 2.6.16 and later.
|
||||
.SH SEE ALSO
|
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.BR numa (3),
|
||||
.BR numactl (8),
|
||||
.BR set_mempolicy (2),
|
||||
.BR get_mempolicy (2),
|
||||
.BR mmap (2)
|
||||
.BR mmap (2),
|
||||
.BR set_mempolicy (2),
|
||||
.BR shmat (2),
|
||||
.BR shmget (2),
|
||||
.BR numa (3),
|
||||
.BR numactl (8)
|
||||
|
|
|
|||
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Reference in New Issue