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_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)
       static 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:

       • explicit memory allocation thanks to hwloc_alloc_membind() and friends: the binding will
         have effect on the memory allocated by these functions.

       • 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.

       • 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_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().

   static 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],  [static]
       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

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