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     domainset(9) — domainset functions and operation


     #include <sys/_domainset.h>
     #include <sys/domainset.h>

           struct domainset {
                   domainset_t     ds_mask;
                   uint16_t        ds_policy;
                   domainid_t      ds_prefer;

     struct domainset *

     struct domainset *

     struct domainset *

     struct domainset *
     domainset_create(const struct domainset *key);



     The domainset(9) API provides memory domain allocation policy for NUMA machines.  Each
     domainset contains a bitmask of allowed domains, an integer policy, and an optional
     preferred domain.  Together, these specify a search order for memory allocations as well as
     the ability to restrict 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 consulted first and the system falls back to the thread policy
     if none exists.

     The allocation policy has the following possible values:

          Memory is allocated from each domain in the mask in a round-robin fashion.  This
          distributes bandwidth evenly among available domains.  This policy can specify a single
          domain for a fixed allocation.

          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.

          Memory is allocated from the node in the prefer member.  The preferred 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.

          Memory is allocated in a striped fashion with multiple pages allocated 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_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_RR() provides round-robin selection among all domains in the system.  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 function.  domainset is an immutable type
     that is shared among all matching keys and must not be modified after return.

     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).


     cpuset(1), cpuset(2), cpuset_setdomain(2), bitset(9)


     <sys/domainset.h> first appeared in FreeBSD 12.0.