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DOMAINSET(9) Kernel Developer's Manual DOMAINSET(9) NAME domainset(9) -- domainset functions and operation SYNOPSIS #include <sys/_domainset.h> #include <sys/domainset.h> struct domainset { domainset_t ds_mask; uint16_t ds_policy; domainid_t ds_prefer; ... }; struct domainset * DOMAINSET_FIXED(domain); struct domainset * DOMAINSET_FT(); struct domainset * DOMAINSET_IL(); struct domainset * DOMAINSET_RR(); struct domainset * DOMAINSET_PREF(domain); struct domainset * domainset_create(const struct domainset *key); int domainset_populate(struct domainset *domain, domainset_t *mask, int policy, size_t mask_size); int sysctl_handle_domainset(SYSCTL_HANDLER_ARGS); DESCRIPTION The domainset(9) API provides memory domain allocation policy for NUMA machines. Each domainset contains a bitmask of allowed domains, an in- teger policy, and an optional preferred domain. Together, these spec- ify a search order for memory allocations as well as the ability to re- strict threads and objects to a subset of available memory domains for system partitioning and resource management. Every thread in the system and optionally every vm_object_t, which is used to represent files and other memory sources, has a reference to a struct domainset. The domainset associated with the object is con- sulted first and the system falls back to the thread policy if none ex- ists. The allocation policy has the following possible values: DOMAINSET_POLICY_ROUNDROBIN Memory is allocated from each domain in the mask in a round-robin fashion. This distributes bandwidth evenly among available do- mains. This policy can specify a single domain for a fixed allo- cation. DOMAINSET_POLICY_FIRSTTOUCH Memory is allocated from the node that it is first accessed on. Allocation falls back to round-robin if the current domain is not in the allowed set or is out of memory. This policy optimizes for locality but may give pessimal results if the memory is accessed from many CPUs that are not in the local domain. DOMAINSET_POLICY_PREFER Memory is allocated from the node in the prefer member. The pre- ferred node must be set in the allowed mask. If the preferred node is out of memory the allocation falls back to round-robin among allowed sets. DOMAINSET_POLICY_INTERLEAVE Memory is allocated in a striped fashion with multiple pages allo- cated to each domain in the set according to the offset within the object. The strip width is object dependent and may be as large as a super-page (2MB on amd64). This gives good distribution among memory domains while keeping system efficiency higher and is preferential to round-robin for general use. The DOMAINSET_FIXED(), DOMAINSET_FT(), DOMAINSET_IL(), DOMAINSET_RR() and DOMAINSET_PREF() macros provide pointers to global pre-defined policies for use when the desired policy is known at compile time. DOMAINSET_FIXED() is a policy which only permits allocations from the specified domain. DOMAINSET_FT() is a policy which attempts to allo- cate memory local to the current CPU, falling back to a round-robin policy if the initial allocation fails. DOMAINSET_IL() and DOMAINSET_RR() provide round-robin selection among all domains in the system, corresponding to the DOMAINSET_POLICY_INTERLEAVE and DOMAINSET_POLICY_ROUNDROBIN policies, respectively. The DOMAINSET_PREF() policies attempt allocation from the specified domain, but unlike DOMAINSET_FIXED() will fall back to other domains to satisfy the request. These policies should be used in preference to DOMAINSET_FIXED() to avoid blocking indefinitely on a M_WAITOK request. The domainset_create() function takes a partially filled in domainset as a key and returns a valid domainset or NULL. It is critical that consumers not use domainsets that have not been returned by this func- tion. domainset is an immutable type that is shared among all matching keys and must not be modified after return. The domainset_populate() function fills a domainset struct using a do- main mask and policy. It is used for validating and translating a do- main mask and policy into a domainset struct when creating a custom do- mainset using domainset_create. The sysctl_handle_domainset() function is provided as a convenience for modifying or viewing domainsets that are not accessible via cpuset(2). It is intended for use with sysctl(9). SEE ALSO cpuset(1), cpuset(2), cpuset_setdomain(2), bitset(9) HISTORY <sys/domainset.h> first appeared in FreeBSD 12.0. FreeBSD 15.0 June 24, 2025 DOMAINSET(9)
NAME | SYNOPSIS | DESCRIPTION | SEE ALSO | HISTORY
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