Ubuntu Manpage: hbwmalloc - The high bandwidth memory interface

Provided by: libmemkind-dev_1.14.0-2_amd64

NAME

       hbwmalloc - The high bandwidth memory interface
       Note: hbwmalloc.h functionality is considered as stable API (STANDARD API).

SYNOPSIS

       #include <hbwmalloc.h>

       Link with -lmemkind

       int hbw_check_available(void);
       void* hbw_malloc(size_t size);
       void* hbw_calloc(size_t nmemb, size_t size);
       void* hbw_realloc (void *ptr, size_t size);
       void hbw_free(void *ptr);
       size_t hbw_malloc_usable_size(void *ptr);
       int hbw_posix_memalign(void **memptr, size_t alignment, size_t size);
       int hbw_posix_memalign_psize(void **memptr, size_t alignment, size_t size, hbw_pagesize_t pagesize);
       hbw_policy_t hbw_get_policy(void);
       int hbw_set_policy(hbw_policy_t mode);
       int hbw_verify_memory_region(void *addr, size_t size, int flags);

DESCRIPTION

hbw_check_available() returns zero if high bandwidth memory is available or an error code
described in the ERRORS section if not.

hbw_malloc() allocates size bytes of uninitialized high bandwidth memory. The allocated
space is suitably aligned (after possible pointer coercion) for storage of any type of
object. If size is zero then hbw_malloc() returns NULL.

hbw_calloc() allocates space for nmemb objects in high bandwidth memory, each size bytes
in length. The result is identical to calling hbw_malloc() with an argument of nmemb *
size, with the exception that the allocated memory is explicitly initialized to zero
bytes. If nmemb or size is 0, then hbw_calloc() returns NULL.

hbw_realloc() changes the size of the previously allocated high bandwidth memory
referenced by ptr to size bytes. The contents of the memory remain unchanged up to the
lesser of the new and old sizes. If the new size is larger, the contents of the newly
allocated portion of the memory are undefined. Upon success, the memory referenced by ptr
is freed and a pointer to the newly allocated high bandwidth memory is returned.

Note: hbw_realloc() may move the memory allocation, resulting in a different return value
than ptr.

If ptr is NULL, the hbw_realloc() function behaves identically to hbw_malloc() for the
specified size. If size is equal to zero, and ptr is not NULL, then the call is
equivalent to hbw_free(ptr) and NULL is returned. The address ptr, if not NULL, was
returned by a previous call to hbw_malloc(), hbw_calloc(), hbw_realloc() or
hbw_posix_memalign(). Otherwise, or if hbw_free(ptr) was called before, undefined
behavior occurs.

Note: hbw_realloc() cannot be used with a pointer returned by hbw_posix_memalign_psize().

hbw_free() causes the allocated memory referenced by ptr to be made available for future
allocations. If ptr is NULL, no action occurs. The address ptr, if not NULL, must have
been returned by a previous call to hbw_malloc(), hbw_calloc(), hbw_realloc(),
hbw_posix_memalign() or hbw_posix_memalign_psize(). Otherwise, if hbw_free(ptr) was
called before, undefined behavior occurs.

hbw_malloc_usable_size() returns the number of usable bytes in the block pointed to by
ptr, a pointer to a block of memory allocated by hbw_malloc(), hbw_calloc(),
hbw_realloc(), hbw_posix_memalign(), or hbw_posix_memalign_psize().

hbw_posix_memalign() allocates size bytes of high bandwidth memory such that the
allocation's base address is an even multiple of alignment, and returns the allocation in
the value pointed to by memptr. The requested alignment must be a power of 2 at least as
large as sizeof(void*). If size is 0, then hbw_posix_memalign() returns 0, with a NULL
returned in memptr.

hbw_posix_memalign_psize() allocates size bytes of high bandwidth memory such that the
allocation's base address is an even multiple of alignment, and returns the allocation in
the value pointed to by memptr. The requested alignment must be a power of 2 at least as
large as sizeof(void*). The memory will be allocated using pages determined by the
pagesize variable which may be one of the following enumerated values:

HBW_PAGESIZE_4KB
The four kilobyte page size option. Note that with transparent huge pages enabled
these allocations may be promoted by the operating system to two megabyte pages.

HBW_PAGESIZE_2MB
The two megabyte page size option. Note: This page size requires huge pages
configuration described in SYSTEM CONFIGURATION section.

HBW_PAGESIZE_1GB (DEPRECATED)
This option allows the user to specify arbitrary sizes backed by 1GB chunks of huge
pages. Huge pages are allocated even if the size is not a modulo of 1GB. Note:
This page size requires huge pages configuration described in SYSTEM CONFIGURATION
section.

HBW_PAGESIZE_1GB_STRICT (DEPRECATED)
The total size of the allocation must be a multiple of 1GB with this option,
otherwise the allocation will fail. Note: This page size requires huge pages
configuration described in SYSTEM CONFIGURATION section.

Note: HBW_PAGESIZE_2MB, HBW_PAGESIZE_1GB and HBW_PAGESIZE_1GB_STRICT options are not
supported with HBW_POLICY_INTERLEAVE policy.

hbw_get_policy() returns the current fallback policy when insufficient high bandwidth
memory is available.

hbw_set_policy() sets the current fallback policy. The policy can be modified only once in
the lifetime of an application and before calling hbw_malloc(), hbw_calloc(),
hbw_realloc(), hbw_posix_memalign(), or hbw_posix_memalign_psize() function.
Note: If the policy is not set, than HBW_POLICY_PREFERRED will be used by default.

HBW_POLICY_BIND
If insufficient high bandwidth memory from the nearest NUMA node is available to
satisfy a request, the allocated pointer is set to NULL and errno is set to ENOMEM.
If insufficient high bandwidth memory pages are available at fault time the Out Of
Memory (OOM) Killer is triggered. Note that pages are faulted exclusively from the
high bandwidth NUMA node nearest at time of allocation, not at time of fault.

HBW_POLICY_BIND_ALL
If insufficient high bandwidth memory is available to satisfy a request, the
allocated pointer is set to NULL and errno is set to ENOMEM. If insufficient high
bandwidth memory pages are available at fault time the Out Of Memory (OOM) Killer
is triggered. Note that pages are faulted from the high bandwidth NUMA nodes.
Nearest NUMA node is selected at time of page fault.

HBW_POLICY_PREFERRED
If insufficient memory is available from the high bandwidth NUMA node closest at
allocation time, fall back to standard memory (default) with the smallest NUMA
distance.

HBW_POLICY_INTERLEAVE
Interleave faulted pages from across all high bandwidth NUMA nodes using standard
size pages (the Transparent Huge Page feature is disabled).

hbw_verify_memory_region() verifies if memory region fully falls into high bandwidth
memory. Returns 0 if memory address range from addr to addr + size is allocated in high
bandwidth memory, -1 if any fragment of memory was not backed by high bandwidth memory
(e.g. when memory is not initialized) or one of error codes described in ERRORS section.

Using this function in production code may result in serious performance penalty.

The Flags argument may include optional flags that modify function behavior:

HBW_TOUCH_PAGES
Before checking pages, function will touch first byte of all pages in address range
starting from addr to addr + size by read and write (so the content will be
overwritten by the same data as it was read). Using this option may trigger Out Of
Memory Killer.

RETURN VALUE

       hbw_get_policy()  returns  HBW_POLICY_BIND,  HBW_POLICY_BIND_ALL,  HBW_POLICY_PREFERRED or
       HBW_POLICY_INTERLEAVE which represents the current high bandwidth policy.   hbw_free()  do
       not  have return value.  hbw_malloc() hbw_calloc() and hbw_realloc() return the pointer to
       the  allocated  memory,   or   NULL   if   the   request   fails.    hbw_posix_memalign(),
       hbw_posix_memalign_psize() and hbw_set_policy() return zero on success and return an error
       code as described in the ERRORS section below on failure.

ERRORS

       Error codes described here are the POSIX standard error codes as defined in
              <errno.h>

       hbw_check_available()
              returns ENODEV if high-bandwidth memory is unavailable.

       hbw_posix_memalign() and hbw_posix_memalign_psize()
              If the alignment parameter is not a  power  of  two,  or  was  not  a  multiple  of
              sizeof(void*),  then EINVAL is returned.  If the policy and pagesize combination is
              unsupported then EINVAL is returned.  If there was insufficient memory  to  satisfy
              the request then ENOMEM is returned.

       hbw_set_policy()
              returns  EPERM  if  hbw_set_policy()  was  called more than once, or EINVAL if mode
              argument was neither HBW_POLICY_PREFERRED, HBW_POLICY_BIND, HBW_POLICY_BIND_ALL nor
              HBW_POLICY_INTERLEAVE.

       hbw_verify_memory_region()
              returns  EINVAL  if  addr is NULL, size equals 0 or flags contained unsupported bit
              set. If memory pointed by addr could not be verified then EFAULT is returned.

NOTES

       The <hbwmalloc.h> file defines the external functions and enumerations for  the  hbwmalloc
       library.  These  interfaces  define a heap manager that targets high bandwidth memory numa
       nodes.

FILES

       /usr/bin/memkind-hbw-nodes
              Prints a comma-separated list of high bandwidth nodes.

ENVIRONMENT

MEMKIND_HBW_NODES
This environment variable is a comma-separated list of NUMA nodes that are treated
as high bandwidth. Uses the libnuma routine numa_parse_nodestring() for parsing, so
the syntax described in the numa(3) man page for this routine applies for example:
1-3,5 is a valid setting.

MEMKIND_ARENA_NUM_PER_KIND
This environment variable allows leveraging internal mechanism of the library for
setting number of arenas per kind. Value should be a positive integer (not greater
than INT_MAX defined in <limits.h>). The user should set the value based on the
characteristics of application that is using the library. Higher value can provide
better performance in extremely multithreaded applications at the cost of memory
overhead. See section IMPLEMENTATION NOTES of jemalloc(3) for more details about
arenas.

MEMKIND_HEAP_MANAGER
Controls heap management behavior in memkind library by switching to one of the
available heap managers.
Values:
JEMALLOC - sets the jemalloc heap manager
TBB - sets the Intel Threading Building Blocks heap manager. This option
requires installed
Intel Threading Building Blocks library.

Note: If the MEMKIND_HEAP_MANAGER is not set then the jemalloc heap manager will be used
by default.

SYSTEM CONFIGURATION

       Interfaces for obtaining 2MB (HUGETLB) memory need allocated huge pages  in  the  kernel's
       huge page pool.

       HUGETLB (huge pages)
              Current    number    of    "persistent"    huge    pages    can    be   read   from
              /proc/sys/vm/nr_hugepages file.  Proposed way of setting hugepages is: sudo  sysctl
              vm.nr_hugepages=<number_of_hugepages>.    More   information  can  be  found  here:
              ⟨https://www.kernel.org/doc/Documentation/vm/hugetlbpage.txt⟩

KNOWN ISSUES

       HUGETLB (huge pages)
              There might be some overhead in huge pages consumption caused by  heap  management.
              If  your  allocation  fails because of OOM, please try to allocate extra huge pages
              (e.g. 8 huge pages).

COPYRIGHT

       Copyright (C) 2014 - 2020 Intel Corporation. All rights reserved.