FreeBSD manual
download PDF document: domainset.9.pdf
DOMAINSET(9) FreeBSD 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
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
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:
DOMAINSET_POLICY_ROUNDROBIN
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.
DOMAINSET_POLICY_FIRSTTOUCH
Memory is allocated from the node that it is first accessed on.
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.
DOMAINSET_POLICY_INTERLEAVE
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_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 allocate
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 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).
SEE ALSO
cpuset(1), cpuset(2), cpuset_setdomain(2), bitset(9)
HISTORY
<sys/domainset.h> first appeared in FreeBSD 12.0.
FreeBSD 14.0-RELEASE-p6 April 14, 2021 FreeBSD 14.0-RELEASE-p6