hwlocality_membinding(3) Library Functions Manual hwlocality_membinding(3)
NAME
hwlocality_membinding - Memory binding
SYNOPSIS
Enumerations
enum hwloc_membind_policy_t { HWLOC_MEMBIND_DEFAULT,
HWLOC_MEMBIND_FIRSTTOUCH, HWLOC_MEMBIND_BIND,
HWLOC_MEMBIND_INTERLEAVE, HWLOC_MEMBIND_WEIGHTED_INTERLEAVE,
HWLOC_MEMBIND_NEXTTOUCH, HWLOC_MEMBIND_MIXED }
enum hwloc_membind_flags_t { HWLOC_MEMBIND_PROCESS,
HWLOC_MEMBIND_THREAD, HWLOC_MEMBIND_STRICT, HWLOC_MEMBIND_MIGRATE,
HWLOC_MEMBIND_NOCPUBIND, HWLOC_MEMBIND_BYNODESET }
Functions
int hwloc_set_membind (hwloc_topology_t topology, hwloc_const_bitmap_t
set, hwloc_membind_policy_t policy, int flags)
int hwloc_get_membind (hwloc_topology_t topology, hwloc_bitmap_t set,
hwloc_membind_policy_t *policy, int flags)
int hwloc_set_proc_membind (hwloc_topology_t topology, hwloc_pid_t pid,
hwloc_const_bitmap_t set, hwloc_membind_policy_t policy, int flags)
int hwloc_get_proc_membind (hwloc_topology_t topology, hwloc_pid_t pid,
hwloc_bitmap_t set, hwloc_membind_policy_t *policy, int flags)
int hwloc_set_area_membind (hwloc_topology_t topology, const void
*addr, size_t len, hwloc_const_bitmap_t set, hwloc_membind_policy_t
policy, int flags)
int hwloc_get_area_membind (hwloc_topology_t topology, const void
*addr, size_t len, hwloc_bitmap_t set, hwloc_membind_policy_t
*policy, int flags)
int hwloc_get_area_memlocation (hwloc_topology_t topology, const void
*addr, size_t len, hwloc_bitmap_t set, int flags)
void * hwloc_alloc (hwloc_topology_t topology, size_t len)
void * hwloc_alloc_membind (hwloc_topology_t topology, size_t len,
hwloc_const_bitmap_t set, hwloc_membind_policy_t policy, int flags)
void * hwloc_alloc_membind_policy (hwloc_topology_t topology, size_t
len, hwloc_const_bitmap_t set, hwloc_membind_policy_t policy, int
flags)
int hwloc_free (hwloc_topology_t topology, void *addr, size_t len)
Detailed Description
Memory binding can be done three ways:
o explicit memory allocation thanks to hwloc_alloc_membind() and
friends: the binding will have effect on the memory allocated by
these functions.
o implicit memory binding through binding policy: hwloc_set_membind()
and friends only define the current policy of the process, which will
be applied to the subsequent calls to malloc() and friends.
o migration of existing memory ranges, thanks to
hwloc_set_area_membind() and friends, which move already-allocated
data.
Not all operating systems support all three ways.
hwloc_topology_get_support() may be used to query about the actual
memory binding support in the currently used operating system.
When the requested binding operation is not available and the
HWLOC_MEMBIND_STRICT flag was passed, the function returns -1. errno
will be set to ENOSYS when the system does support the specified action
or policy (e.g., some systems only allow binding memory on a per-thread
basis, whereas other systems only allow binding memory for all threads
in a process). errno will be set to EXDEV when the requested set can
not be enforced (e.g., some systems only allow binding memory to a
single NUMA node).
If HWLOC_MEMBIND_STRICT was not passed, the function may fail as well,
or the operating system may use a slightly different operation (with
side-effects, smaller binding set, etc.) when the requested operation
is not exactly supported.
The most portable form that should be preferred over the others
whenever possible is as follows. It allocates some memory hopefully
bound to the specified set. To do so, hwloc will possibly have to
change the current memory binding policy in order to actually get the
memory bound, if the OS does not provide any other way to simply
allocate bound memory without changing the policy for all allocations.
That is the difference with hwloc_alloc_membind(), which will never
change the current memory binding policy.
hwloc_alloc_membind_policy(topology, size, set,
HWLOC_MEMBIND_BIND, 0);
Each hwloc memory binding function takes a bitmap argument that is a
CPU set by default, or a NUMA memory node set if the flag
HWLOC_MEMBIND_BYNODESET is specified. See Object Sets (hwloc_cpuset_t
and hwloc_nodeset_t) and The bitmap API for a discussion of CPU sets
and NUMA memory node sets. It is also possible to convert between CPU
set and node set using hwloc_cpuset_to_nodeset() or
hwloc_cpuset_from_nodeset().
Memory binding by CPU set cannot work for CPU-less NUMA memory nodes.
Binding by nodeset should therefore be preferred whenever possible.
See also
Some example codes are available under doc/examples/ in the source
tree.
Note
On some operating systems, memory binding affects the CPU binding;
see HWLOC_MEMBIND_NOCPUBIND
Enumeration Type Documentation
enum hwloc_membind_flags_t
Memory binding flags. These flags can be used to refine the binding
policy. All flags can be logically OR'ed together with the exception of
HWLOC_MEMBIND_PROCESS and HWLOC_MEMBIND_THREAD; these two flags are
mutually exclusive.
Not all systems support all kinds of binding.
hwloc_topology_get_support() may be used to query about the actual
memory binding support in the currently used operating system. See the
'Detailed Description' section of Memory binding for a description of
errors that can occur.
Enumerator
HWLOC_MEMBIND_PROCESS
Set policy for all threads of the specified (possibly
multithreaded) process. This flag is mutually exclusive with
HWLOC_MEMBIND_THREAD.
HWLOC_MEMBIND_THREAD
Set policy for a specific thread of the current process. This
flag is mutually exclusive with HWLOC_MEMBIND_PROCESS.
HWLOC_MEMBIND_STRICT
Request strict binding from the OS. The function will fail if
the binding can not be guaranteed / completely enforced.
This flag has slightly different meanings depending on which function
it is used with.
HWLOC_MEMBIND_MIGRATE
Migrate existing allocated memory. If the memory cannot be
migrated and the HWLOC_MEMBIND_STRICT flag is passed, an error
will be returned.
HWLOC_MEMBIND_NOCPUBIND
Avoid any effect on CPU binding. On some operating systems, some
underlying memory binding functions also bind the application to
the corresponding CPU(s). Using this flag will cause hwloc to
avoid using OS functions that could potentially affect CPU
bindings. Note, however, that using NOCPUBIND may reduce hwloc's
overall memory binding support. Specifically: some of hwloc's
memory binding functions may fail with errno set to ENOSYS when
used with NOCPUBIND.
HWLOC_MEMBIND_BYNODESET
Consider the bitmap argument as a nodeset. The bitmap argument
is considered a nodeset if this flag is given, or a cpuset
otherwise by default.
Memory binding by CPU set cannot work for CPU-less NUMA memory nodes.
Binding by nodeset should therefore be preferred whenever possible.
enum hwloc_membind_policy_t
Memory binding policy. These constants can be used to choose the
binding policy. Only one policy can be used at a time (i.e., the values
cannot be OR'ed together).
Not all systems support all kinds of binding.
hwloc_topology_get_support() may be used to query about the actual
memory binding policy support in the currently used operating system.
See the 'Detailed Description' section of Memory binding for a
description of errors that can occur.
Enumerator
HWLOC_MEMBIND_DEFAULT
Reset the memory allocation policy to the system default.
Depending on the operating system, this may correspond to
HWLOC_MEMBIND_FIRSTTOUCH (Linux, FreeBSD), or HWLOC_MEMBIND_BIND
(AIX, HP-UX, Solaris, Windows). This policy is never returned by
get membind functions. The nodeset argument is ignored.
HWLOC_MEMBIND_FIRSTTOUCH
Allocate each memory page individually on the local NUMA node of
the thread that touches it. The given nodeset should usually be
hwloc_topology_get_topology_nodeset() so that the touching
thread may run and allocate on any node in the system.
On AIX, if the nodeset is smaller, pages are allocated locally (if the
local node is in the nodeset) or from a random non-local node
(otherwise).
HWLOC_MEMBIND_BIND
Allocate memory on the specified nodes. The actual behavior may
slightly vary between operating systems, especially when (some
of) the requested nodes are full. On Linux, by default, the
MPOL_PREFERRED_MANY (or MPOL_PREFERRED) policy is used. However,
if the hwloc strict flag is also given, the Linux MPOL_BIND
policy is rather used.
HWLOC_MEMBIND_INTERLEAVE
Allocate memory on the given nodes in an interleaved / round-
robin manner. The precise layout of the memory across multiple
NUMA nodes is OS/system specific. Interleaving can be useful
when threads distributed across the specified NUMA nodes will
all be accessing the whole memory range concurrently, since the
interleave will then balance the memory references.
HWLOC_MEMBIND_WEIGHTED_INTERLEAVE
Allocate memory on the given nodes in an interleaved / weighted
manner. The precise layout of the memory across multiple NUMA
nodes is OS/system specific. Weighted interleaving can be useful
when threads distributed across the specified NUMA nodes with
different bandwidth capabilities will all be accessing the whole
memory range concurrently, since the interleave will then
balance the memory references.
HWLOC_MEMBIND_NEXTTOUCH
For each page bound with this policy, by next time it is touched
(and next time only), it is moved from its current location to
the local NUMA node of the thread where the memory reference
occurred (if it needs to be moved at all).
HWLOC_MEMBIND_MIXED
Returned by get_membind() functions when multiple threads or
parts of a memory area have differing memory binding policies.
Also returned when binding is unknown because binding hooks are
empty when the topology is loaded from XML without
HWLOC_THISSYSTEM=1, etc.
Function Documentation
void * hwloc_alloc (hwloc_topology_t topology, size_t len)
Allocate some memory. This is equivalent to malloc(), except that it
tries to allocate page-aligned memory from the OS.
Returns
a pointer to the allocated area, or NULL on error.
Note
The allocated memory should be freed with hwloc_free().
void * hwloc_alloc_membind (hwloc_topology_t topology, size_t len,
hwloc_const_bitmap_t set, hwloc_membind_policy_t policy, int flags)
Allocate some memory on NUMA memory nodes specified by set.
Returns
a pointer to the allocated area.
NULL with errno set to ENOSYS if the action is not supported and
HWLOC_MEMBIND_STRICT is given.
NULL with errno set to EXDEV if the binding cannot be enforced and
HWLOC_MEMBIND_STRICT is given.
NULL with errno set to ENOMEM if the memory allocation failed even
before trying to bind.
If HWLOC_MEMBIND_BYNODESET is specified, set is considered a nodeset.
Otherwise it's a cpuset.
Note
The allocated memory should be freed with hwloc_free().
void * hwloc_alloc_membind_policy (hwloc_topology_t topology, size_t len,
hwloc_const_bitmap_t set, hwloc_membind_policy_t policy, int flags)
[inline]
Allocate some memory on NUMA memory nodes specified by set. First, try
to allocate properly with hwloc_alloc_membind(). On failure, the
current process or thread memory binding policy is changed with
hwloc_set_membind() before allocating memory. Thus this function works
in more cases, at the expense of changing the current state (possibly
affecting future allocations that would not specify any policy).
If HWLOC_MEMBIND_BYNODESET is specified, set is considered a nodeset.
Otherwise it's a cpuset.
Returns
a pointer to the allocated area, or NULL on error.
int hwloc_free (hwloc_topology_t topology, void * addr, size_t len)
Free memory that was previously allocated by hwloc_alloc() or
hwloc_alloc_membind().
Returns
0 on success, -1 on error.
int hwloc_get_area_membind (hwloc_topology_t topology, const void * addr,
size_t len, hwloc_bitmap_t set, hwloc_membind_policy_t * policy, int
flags)
Query the CPUs near the physical NUMA node(s) and binding policy of the
memory identified by (addr, len ). The bitmap set (previously allocated
by the caller) is filled with the memory area binding.
This function has two output parameters: set and policy. The values
returned in these parameters depend on both the flags passed in and the
memory binding policies and nodesets of the pages in the address range.
If HWLOC_MEMBIND_STRICT is specified, the target pages are first
checked to see if they all have the same memory binding policy and
nodeset. If they do not, -1 is returned and errno is set to EXDEV. If
they are identical across all pages, the set and policy are returned in
set and policy, respectively.
If HWLOC_MEMBIND_STRICT is not specified, the union of all NUMA node(s)
containing pages in the address range is calculated. If all pages in
the target have the same policy, it is returned in policy. Otherwise,
policy is set to HWLOC_MEMBIND_MIXED.
If HWLOC_MEMBIND_BYNODESET is specified, set is considered a nodeset.
Otherwise it's a cpuset.
If any other flags are specified, -1 is returned and errno is set to
EINVAL.
Returns
0 on success.
-1 with errno set to EINVAL if len is 0.
int hwloc_get_area_memlocation (hwloc_topology_t topology, const void *
addr, size_t len, hwloc_bitmap_t set, int flags)
Get the NUMA nodes where memory identified by (addr, len ) is
physically allocated. The bitmap set (previously allocated by the
caller) is filled according to the NUMA nodes where the memory area
pages are physically allocated. If no page is actually allocated yet,
set may be empty.
If pages spread to multiple nodes, it is not specified whether they
spread equitably, or whether most of them are on a single node, etc.
The operating system may move memory pages from one processor to
another at any time according to their binding, so this function may
return something that is already outdated.
If HWLOC_MEMBIND_BYNODESET is specified in flags, set is considered a
nodeset. Otherwise it's a cpuset.
If len is 0, set is emptied.
Returns
0 on success, -1 on error.
int hwloc_get_membind (hwloc_topology_t topology, hwloc_bitmap_t set,
hwloc_membind_policy_t * policy, int flags)
Query the default memory binding policy and physical locality of the
current process or thread. The bitmap set (previously allocated by the
caller) is filled with the process or thread memory binding.
This function has two output parameters: set and policy. The values
returned in these parameters depend on both the flags passed in and the
current memory binding policies and nodesets in the queried target.
Passing the HWLOC_MEMBIND_PROCESS flag specifies that the query target
is the current policies and nodesets for all the threads in the current
process. Passing HWLOC_MEMBIND_THREAD specifies that the query target
is the current policy and nodeset for only the thread invoking this
function.
If neither of these flags are passed (which is the most portable
method), the process is assumed to be single threaded. This allows
hwloc to use either process-based OS functions or thread-based OS
functions, depending on which are available.
HWLOC_MEMBIND_STRICT is only meaningful when HWLOC_MEMBIND_PROCESS is
also specified. In this case, hwloc will check the default memory
policies and nodesets for all threads in the process. If they are not
identical, -1 is returned and errno is set to EXDEV. If they are
identical, the values are returned in set and policy.
Otherwise, if HWLOC_MEMBIND_PROCESS is specified (and
HWLOC_MEMBIND_STRICT is not specified), the default set from each
thread is logically OR'ed together. If all threads' default policies
are the same, policy is set to that policy. If they are different,
policy is set to HWLOC_MEMBIND_MIXED.
In the HWLOC_MEMBIND_THREAD case (or when neither HWLOC_MEMBIND_PROCESS
or HWLOC_MEMBIND_THREAD is specified), there is only one set and
policy; they are returned in set and policy, respectively.
If HWLOC_MEMBIND_BYNODESET is specified, set is considered a nodeset.
Otherwise it's a cpuset.
If any other flags are specified, -1 is returned and errno is set to
EINVAL.
Returns
0 on success, -1 on error.
int hwloc_get_proc_membind (hwloc_topology_t topology, hwloc_pid_t pid,
hwloc_bitmap_t set, hwloc_membind_policy_t * policy, int flags)
Query the default memory binding policy and physical locality of the
specified process. The bitmap set (previously allocated by the caller)
is filled with the process memory binding.
This function has two output parameters: set and policy. The values
returned in these parameters depend on both the flags passed in and the
current memory binding policies and nodesets in the queried target.
Passing the HWLOC_MEMBIND_PROCESS flag specifies that the query target
is the current policies and nodesets for all the threads in the
specified process. If HWLOC_MEMBIND_PROCESS is not specified (which is
the most portable method), the process is assumed to be single
threaded. This allows hwloc to use either process-based OS functions or
thread-based OS functions, depending on which are available.
Note that it does not make sense to pass HWLOC_MEMBIND_THREAD to this
function.
If HWLOC_MEMBIND_STRICT is specified, hwloc will check the default
memory policies and nodesets for all threads in the specified process.
If they are not identical, -1 is returned and errno is set to EXDEV. If
they are identical, the values are returned in set and policy.
Otherwise, set is set to the logical OR of all threads' default set. If
all threads' default policies are the same, policy is set to that
policy. If they are different, policy is set to HWLOC_MEMBIND_MIXED.
If HWLOC_MEMBIND_BYNODESET is specified, set is considered a nodeset.
Otherwise it's a cpuset.
If any other flags are specified, -1 is returned and errno is set to
EINVAL.
Returns
0 on success, -1 on error.
Note
hwloc_pid_t is pid_t on Unix platforms, and HANDLE on native
Windows platforms.
int hwloc_set_area_membind (hwloc_topology_t topology, const void * addr,
size_t len, hwloc_const_bitmap_t set, hwloc_membind_policy_t policy,
int flags)
Bind the already-allocated memory identified by (addr, len) to the NUMA
node(s) specified by set. If HWLOC_MEMBIND_BYNODESET is specified, set
is considered a nodeset. Otherwise it's a cpuset.
Returns
0 on success or if len is 0.
-1 with errno set to ENOSYS if the action is not supported.
-1 with errno set to EXDEV if the binding cannot be enforced.
int hwloc_set_membind (hwloc_topology_t topology, hwloc_const_bitmap_t set,
hwloc_membind_policy_t policy, int flags)
Set the default memory binding policy of the current process or thread
to prefer the NUMA node(s) specified by set. If neither
HWLOC_MEMBIND_PROCESS nor HWLOC_MEMBIND_THREAD is specified, the
current process is assumed to be single-threaded. This is the most
portable form as it permits hwloc to use either process-based OS
functions or thread-based OS functions, depending on which are
available.
If HWLOC_MEMBIND_BYNODESET is specified, set is considered a nodeset.
Otherwise it's a cpuset.
Returns
0 on success.
-1 with errno set to ENOSYS if the action is not supported.
-1 with errno set to EXDEV if the binding cannot be enforced.
int hwloc_set_proc_membind (hwloc_topology_t topology, hwloc_pid_t pid,
hwloc_const_bitmap_t set, hwloc_membind_policy_t policy, int flags)
Set the default memory binding policy of the specified process to
prefer the NUMA node(s) specified by set. If HWLOC_MEMBIND_BYNODESET is
specified, set is considered a nodeset. Otherwise it's a cpuset.
Returns
0 on success.
-1 with errno set to ENOSYS if the action is not supported.
-1 with errno set to EXDEV if the binding cannot be enforced.
Note
hwloc_pid_t is pid_t on Unix platforms, and HANDLE on native
Windows platforms.
Author
Generated automatically by Doxygen for Hardware Locality (hwloc) from
the source code.
Hardware Locality (hwloc) Version 2.12.0 hwlocality_membinding(3)
hwloc 2.12.0 - Generated Fri May 9 07:18:38 CDT 2025