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32 .Nd domainset functions and operation
37 .Bd -literal -offset indent
47 .Fn DOMAINSET_PREF domain
48 .Ft struct domainset *
49 .Fn domainset_create "const struct domainset *key"
51 .Fn sysctl_handle_domainset "SYSCTL_HANDLER_ARGS"
55 API provides memory domain allocation policy for NUMA machines.
58 contains a bitmask of allowed domains, an integer policy, and an optional
60 Together, these specify a search order for memory allocations as well as
61 the ability to restrict threads and objects to a subset of available
62 memory domains for system partitioning and resource management.
64 Every thread in the system and optionally every
66 which is used to represent files and other memory sources, has
68 .Vt struct domainset .
69 The domainset associated with the object is consulted first and the system
70 falls back to the thread policy if none exists.
72 The allocation policy has the following possible values:
74 .It Dv DOMAINSET_POLICY_ROUNDROBIN
75 Memory is allocated from each domain in the mask in a round-robin fashion.
76 This distributes bandwidth evenly among available domains.
77 This policy can specify a single domain for a fixed allocation.
78 .It Dv DOMAINSET_POLICY_FIRSTTOUCH
79 Memory is allocated from the node that it is first accessed on.
80 Allocation falls back to round-robin if the current domain is not in the
81 allowed set or is out of memory.
82 This policy optimizes for locality but may give pessimal results if the
83 memory is accessed from many CPUs that are not in the local domain.
84 .It Dv DOMAINSET_POLICY_PREFER
85 Memory is allocated from the node in the
87 member. The preferred node must be set in the allowed mask.
88 If the preferred node is out of memory the allocation falls back to
89 round-robin among allowed sets.
90 .It Dv DOMAINSET_POLICY_INTERLEAVE
91 Memory is allocated in a striped fashion with multiple pages
92 allocated to each domain in the set according to the offset within
94 The strip width is object dependent and may be as large as a
95 super-page (2MB on amd64).
96 This gives good distribution among memory domains while keeping system
97 efficiency higher and is preferential to round-robin for general use.
104 provide pointers to global pre-defined policies for use when the
105 desired policy is known at compile time.
108 function takes a partially filled in domainset as a key and returns a
109 valid domainset or NULL.
110 It is critical that consumers not use domainsets that have not been
111 returned by this function.
114 is an immutable type that is shared among all matching keys and must
115 not be modified after return.
118 .Fn sysctl_handle_domainset
119 function is provided as a convenience for modifying or viewing domainsets
120 that are not accessible via
122 It is intended for use with
128 .Xr cpuset_setdomain 2 ,