LIBMEMTIER C API(3)

NAME
libmemtier - memory tiering interface
Note: memkind_memtier.h functionality is considered as stable API (STANDARD API).

SYNOPSIS
#include <memkind_memtier.h>

Link with -lmemkind

The API can be used either directly with the usage of C-functions or via environment variables. See also ENVIRONMENT section.

TIER MANAGEMENT:

struct memtier_builder *memtier_builder_new(memtier_policy_t policy);
void memtier_builder_delete(struct memtier_builder *builder);
int memtier_builder_add_tier(struct memtier_builder *builder, memkind_t kind, unsigned kind_ratio);
struct memtier_memory *memtier_builder_construct_memtier_memory(struct memtier_builder *builder);
void memtier_delete_memtier_memory(struct memtier_memory *memory);

HEAP MANAGEMENT:
void *memtier_malloc(struct memtier_memory *memory, size_t size);
void *memtier_kind_malloc(memkind_t kind, size_t size);
void *memtier_calloc(struct memtier_memory *memory, size_t num, size_t size);
void *memtier_kind_calloc(memkind_t kind, size_t num, size_t size);
void *memtier_realloc(struct memtier_memory *memory, void *ptr, size_t size);
void *memtier_kind_realloc(memkind_t kind, void *ptr, size_t size);
int memtier_posix_memalign(struct memtier_memory *memory, void **memptr, size_t alignment, size_t size);
int memtier_kind_posix_memalign(memkind_t kind, void **memptr, size_t alignment, size_t size);
size_t memtier_usable_size(void *ptr);
void memtier_free(void *ptr);
void memtier_kind_free(memkind_t kind, void *ptr);
size_t memtier_kind_allocated_size(memkind_t kind);

DECORATORS:
void memtier_kind_malloc_post(memkind_t kind, size_t size, void **result);
void memtier_kind_calloc_post(memkind_t kind, size_t nmemb, size_t size, void **result);
void memtier_kind_posix_memalign_post(memkind_t kind, void **memptr, size_t alignment, size_t size, int *err);
void memtier_kind_realloc_post(memkind_t *kind, void *ptr, size_t size, void **result);
void memtier_kind_free_pre(void **ptr);
void memtier_kind_usable_size_post(void **ptr, size_t size);

MEMTIER PROPERTY MANAGEMENT:
int memtier_ctl_set(struct memtier_builder *builder, const char *name, const void *val);

DESCRIPTION
This library enables explicit allocation-time memory tiering. It allows to make allocations with the usage of multiple kinds keeping a specified ratio between them. This ratio determines how much of total allocated memory should be allocated with the usage of each kind.

TIER MANAGEMENT:
The functions in this section are used to set up, create and destroy the memtier_memory object. This object is passed as an argument to the memtier_malloc() group of functions. It defines the way the allocations are distributed between different memory tiers.

memtier_builder_new() returns a pointer to a new memtier_builder object which is used for creating the memtier_memory object, policy determines the policy of allocations distribution between tiers by the memtier_memory object. See the POLICIES section in libmemtier(7) for available options.

memtier_builder_delete() deletes the builder object releasing the memory it used. Use after the memtier_memory object is created with the function memtier_builder_construct_memtier_memory().

memtier_builder_add_tier() adds memory kind to the builder. This kind defines a memory tier used in the memtier_memory object. This function can be called more than once to create several different memory tiers. The "weight" of the tier is determined by the kind_ratio parameter. The higher it is relative to other tiers' kind_ratio, the higher the share of allocated memory on that tier, e.g. given that ratio DRAM:KMEM_DAX is 1:4:

    sample allocation size: 20 GB total, 4 GB DRAM, 16 GB KMEM_DAX

memtier_builder_construct_memtier_memory() returns a pointer to a newly allocated memtier_memory object. The builder can be safely removed after this operation using the memtier_builder_delete() function.

memtier_delete_memtier_memory() deletes the memory tiering object releasing the memory it used.

HEAP MANAGEMENT:
The functions described in this section define a heap manager with an interface modeled on the ISO C standard API's, except that the user must specify either the kind of memory with the first argument to each function or the tiered memory object which defines memory tiers used for allocations. See the KINDS section in the memkind(3) manual for a full description of the implemented kinds.

memtier_malloc() allocates size bytes of memory on one of memory tiers defined by the memory. See libmemtier(7) for further details on memory tiers. memkind_malloc() is used for allocations. For further details on it's behavior see memkind(3).

memtier_kind_malloc() is a wrapper to the memkind_malloc() function. See memkind(3) for further details.

memtier_calloc() allocates num times size bytes of memory on one of memory tiers defined by the memory. memkind_calloc() is used for allocations. For further details on it's behavior see memkind(3).

memtier_kind_calloc() is a wrapper to the memkind_calloc() function. See memkind(3) for further details.

memtier_realloc() changes the size of the previously allocated memory referenced by ptr to size bytes using memory from the tier on which ptr is allocated. If ptr is NULL, new memory is allocated on a memory tier defined by memory. memkind_realloc() is used for reallocation. See memkind(3) for further details.

memtier_kind_realloc() changes the size of the previously allocated memory referenced by ptr to size bytes using specific kind. If size is equal to zero and ptr is not NULL, then the call is equivalent to memkind_free(kind, ptr) and NULL is returned. If ptr is NULL, memtier_kind_malloc() is called to allocate new memory. Otherwise, the memkind_realloc() function is used. See memkind(3) for further details.

memtier_posix_memalign() is a wrapper of memkind_posix_memalign() with the main difference that the memory is used to determine the kind to be used for the allocation. See memkind(3) for further details.

memtier_kind_posix_memalign() is a wrapper of memkind_posix_memalign(). See memkind(3) for further details.

memtier_usable_size() returns the size of the block of memory allocated with the memtier API at the address pointed by ptr.

memtier_free() is a wrapper for the memtier_kind_free() function with the kind parameter passed as NULL.

memtier_kind_free() frees up the memory pointed to by ptr. The behavior is the same as for the memkind_free(). If kind is NULL, the kind used to allocate ptr is detected automatically. See memkind(3) for further details.

memtier_kind_allocated_size() returns the total size of memory allocated with the usage of kind and the memtier API.

DECORATORS:
This is the set of functions used to print information on each call to the respective memtier_kind_* function described in the HEAP MANAGEMENT section. Printed information include the name of the kind used, parameters passed to the underlying function from the malloc family of functions and the address of the memory returned.

MEMTIER PROPERTY MANAGEMENT:
memtier_ctl_set() is useful for changing the default values of parameters that define the DYNAMIC_THRESHOLD policy. This function can be used in the process of creating a memtier_memory object with the usage of builder. The parameter name can be one of the following:

policy.dynamic_threshold.thresholds[ID].val
    initial threshold level, all alocations of the size below this value will come from the IDth tier, greater than or equal to this value will come from the (ID+1)th tier. Provided string is converted to the size_t type. This value is modified automatically during the application run to keep the desired ratio between tiers. The default value between first two tiers is 1024 bytes

policy.dynamic_threshold.thresholds[ID].min
    minimum value of the threshold level. Provided string is converted to the size_t type. The default value between first two tiers is 513 bytes.

policy.dynamic_threshold.thresholds[ID].max
    maximum value of the threshold level. Provided string is converted to the size_t type. The default value between first two tiers is 1536 bytes.

policy.dynamic_threshold.check_cnt
    number of allocation operations (i.e. malloc, realloc) after which the ratio check between tiers is performed. Provided string is converted to the unsigned int type. The default value is 20.

policy.dynamic_threshold.trigger
    the dynamic threshold value is adjusted when the absolute difference between current ratio and expected ratio is greater than or equal to this value. Provided string is converted to the float type. The default value is 0.02.

policy.dynamic_threshold.degree
    the threshold value is updated by increasing or decreasing it's value by degree percentage (i.e. degree=0.02 changes threshold value by 2%). Provided string is converted to the float type. The default value is 0.15.

In the above examples, ID should be replaced with the ID of thresholds configuration. The configuration between first two tiers added to builder has an ID equal to 0. The configuration ID of the next two tiers, that is, the second and third ones, is equal to 1, and so on. The last configuration's ID is equal to the number of tiers minus one.

ENVIRONMENT
See libmemtier(7) for details on the usage of memkind tiering via environment variables.

COPYRIGHT
Copyright (C) 2021-2022 Intel Corporation. All rights reserved.

SEE ALSO
libmemtier(7), memkind(3), memkind_malloc(3), memkind_calloc(3), memkind_realloc(3), memkind_free(3), memkind_posix_memalign(3)