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LIBMEMSTAT(3)		 BSD Library Functions Manual		 LIBMEMSTAT(3)

NAME
     libmemstat — library interface to retrieve kernel memory allocator sta‐
     tistics

LIBRARY
     library “libmemstat”

SYNOPSIS
     #include <sys/types.h>
     #include <memstat.h>

   General Functions
     const char *
     memstat_strerror(int error);

   Memory Type List Management Functions
     struct memory_type_list *
     memstat_mtl_alloc(void);

     struct memory_type *
     memstat_mtl_first(struct memory_type_list *list);

     struct memory_type *
     memstat_mtl_next(struct memory_type *mtp);

     struct memory_type *
     memstat_mtl_find(struct memory_type_list *list, int allocator,
	 const char *name);

     void
     memstat_mtl_free(struct memory_type_list *list);

     int
     memstat_mtl_geterror(struct memory_type_list *list);

   Allocator Query Functions
     int
     memstat_kvm_all(struct memory_type_list *list, void *kvm_handle);

     int
     memstat_kvm_malloc(struct memory_type_list *list, void *kvm_handle);

     int
     memstat_kvm_uma(struct memory_type_list *list, void *kvm_handle);

     int
     memstat_sysctl_all(struct memory_type_list *list, int flags);

     int
     memstat_sysctl_malloc(struct memory_type_list *list, int flags);

     int
     memstat_sysctl_uma(struct memory_type_list *list, int flags);

   Memory Type Accessor Methods
     const char *
     memstat_get_name(const struct memory_type *mtp);

     int
     memstat_get_allocator(const struct memory_type *mtp);

     uint64_t
     memstat_get_countlimit(const struct memory_type *mtp);

     uint64_t
     memstat_get_byteslimit(const struct memory_type *mtp);

     uint64_t
     memstat_get_sizemask(const struct memory_type *mtp);

     uint64_t
     memstat_get_size(const struct memory_type *mtp);

     uint64_t
     memstat_get_memalloced(const struct memory_type *mtp);

     uint64_t
     memstat_get_memfreed(const struct memory_type *mtp);

     uint64_t
     memstat_get_numallocs(const struct memory_type *mtp);

     uint64_t
     memstat_get_numfrees(const struct memory_type *mtp);

     uint64_t
     memstat_get_bytes(const struct memory_type *mtp);

     uint64_t
     memstat_get_count(const struct memory_type *mtp);

     uint64_t
     memstat_get_free(const struct memory_type *mtp);

     uint64_t
     memstat_get_failures(const struct memory_type *mtp);

     void *
     memstat_get_caller_pointer(const struct memory_type *mtp, int index);

     void
     memstat_set_caller_pointer(struct memory_type *mtp, int index,
	 void *value);

     uint64_t
     memstat_get_caller_uint64(const struct memory_type *mtp, int index);

     void
     memstat_set_caller_uint64(struct memory_type *mtp, int index,
	 uint64_t value);

     uint64_t
     memstat_get_zonefree(const struct memory_type *mtp);

     uint64_t
     memstat_get_kegfree(const struct memory_type *mtp);

     uint64_t
     memstat_get_percpu_memalloced(const struct memory_type *mtp, int cpu);

     uint64_t
     memstat_get_percpu_memfreed(const struct memory_type *mtp, int cpu);

     uint64_t
     memstat_get_percpu_numallocs(const struct memory_type *mtp, int cpu);

     uint64_t
     memstat_get_percpu_numfrees(const struct memory_type *mtp, int cpu);

     uint64_t
     memstat_get_percpu_sizemask(const struct memory_type *mtp, int cpu);

     void *
     memstat_get_percpu_caller_pointer(const struct memory_type *mtp, int cpu,
	 int index);

     void
     memstat_set_percpu_caller_pointer(struct memory_type *mtp, int cpu,
	 int index, void *value);

     uint64_t
     memstat_get_percpu_caller_uint64(const struct memory_type *mtp, int cpu,
	 int index);

     void
     memstat_set_percpu_caller_uint64(struct memory_type *mtp, int cpu,
	 int index, uint64_t value);

     uint64_t
     memstat_get_percpu_free(const struct memory_type *mtp, int cpu);

DESCRIPTION
     libmemstat provides an interface to retrieve kernel memory allocator sta‐
     tistics, for the purposes of debugging and system monitoring, insulating
     applications from implementation details of the allocators, and allowing
     a tool to transparently support multiple allocators.  libmemstat supports
     both retrieving a single statistics snapshot, as well as incrementally
     updating statistics for long-term monitoring.

     libmemstat describes each memory type using a struct memory_type, an
     opaque memory type accessed by the application using accessor functions
     in the library.  libmemstat returns and updates chains of struct
     memory_type via a struct memory_type_list, which will be allocated by
     calling memstat_mtl_alloc(), and freed on completion using
     memstat_mtl_free().  Lists of memory types are populated via calls that
     query the kernel for statistics information; currently:
     memstat_kvm_all(), memstat_kvm_malloc(), memstat_kvm_uma(),
     memstat_sysctl_all(), memstat_sysctl_uma(), and memstat_sysctl_malloc().
     Repeated calls will incrementally update the list of memory types, per‐
     mitting tracking over time without recreating all list state.  If an
     error is detected during a query call, error condition information may be
     retrieved using memstat_mtl_geterror(), and converted to a user-readable
     string using memstat_strerror().

     Freeing the list will free all memory type data in the list, and so
     invalidates any outstanding pointers to entries in the list.  struct
     memory_type entries in the list may be iterated over using
     memstat_mtl_first() and memstat_mtl_next(), which respectively return the
     first entry in a list, and the next entry in a list.  memstat_mtl_find(),
     which will return a pointer to the first entry matching the passed param‐
     eters.

     A series of accessor methods is provided to access fields of the struc‐
     ture, including retrieving statistics and properties, as well as setting
     of caller owned fields.  Direct application access to the data structure
     fields is not supported.

   Library memory_type Fields
     Each struct memory_type holds a description of the memory type, including
     its name and the allocator it is managed by, as well as current statis‐
     tics on use.  Some statistics are directly measured, others are derived
     from directly measured statistics.	 Certain high level statistics are
     present across all available allocators, such as the number of allocation
     and free operations; other measurements, such as the quantity of free
     items in per-CPU caches, or administrative limit on the number of alloca‐
     tions, is available only for specific allocators.

   Caller memory_type Fields
     struct memory_type includes fields to allow the application to store
     data, in the form of pointers and 64-bit integers, with memory types.
     For example, the application author might make use of one of the caller
     pointers to reference a more complex data structure tracking long-term
     behavior of the memory type, or a window system object that is used to
     render the state of the memory type.  General and per-CPU storage is pro‐
     vided with each struct memory_type in the form of an array of pointers
     and integers.  The array entries are accessed via the index argument to
     the get and set accessor methods.	Possible values of index range between
     0 and MEMSTAT_MAXCALLER.

     Caller-owned fields are initialized to 0 or NULL when a new struct
     memory_type is allocated and attached to a memory type list; these fields
     retain their values across queries that update library-owned fields.

   Allocator Types
     Currently, libmemstat supports two kernel allocators: ALLOCATOR_UMA for
     uma(9), and ALLOCATOR_MALLOC for malloc(9).  These values may be passed
     to memstat_mtl_find(), and will be returned by memstat_get_allocator().
     Two additional constants in the allocator name space are defined:
     ALLOCATOR_UNKNOWN, which will only be returned as a result of a library
     error, and ALLOCATOR_ANY, which can be used to specify that returning
     types matching any allocator is permittible from memstat_mtl_find().

   Access Method List
     The following accessor methods are defined, of which some will be valid
     for a given memory type:

     memstat_get_name()
	     Return a pointer to the name of the memory type.  Memory for the
	     name is owned by libmemstat and will be valid through a call to
	     memstat_mtl_free().  Note that names will be unique with respect
	     to a single allocator, but that the same name might be used by
	     different memory types owned by different memory allocators.

     memstat_get_allocator()
	     Return an integer identifier for the memory allocator that owns
	     the memory type.

     memstat_get_countlimit()
	     If the memory type has an administrative limit on the number of
	     simultaneous allocations, return it.

     memstat_get_byteslimit()
	     If the memory type has an administrative limit on the number of
	     bytes of memory that may be simultaenously allocated for the mem‐
	     ory type, return it.

     memstat_get_sizemask()
	     If the memory type supports variable allocation sizes, return a
	     bitmask of sizes allocated for the memory type.

     memstat_get_size()
	     If the memory type supports a fixed allocation size, return that
	     size.

     memstat_get_memalloced()
	     Return the total number of bytes allocated for the memory type
	     over its lifetime.

     memstat_get_memfreed()
	     Return the total number of bytes freed for the memory type over
	     its lifetime.

     memstat_get_numallocs()
	     Return the total number of allocations for the memory type over
	     its lifetime.

     memstat_get_numfrees()
	     Return the total number of frees for the memory type over its
	     lifetime.

     memstat_get_bytes()
	     Return the current number of bytes allocated to the memory type.

     memstat_get_count()
	     Return the current number of allocations for the memory type.

     memstat_get_free()
	     If the memory allocator supports a cache, return the number of
	     items in the cache.

     memstat_get_failures()
	     If the memory allocator and type permit allocation failures,
	     return the number of allocation failures measured.

     memstat_get_caller_pointer()
	     Return a caller-owned pointer for the memory type.

     memstat_set_caller_pointer()
	     Set a caller-owned pointer for the memory type.

     memstat_get_caller_uint64()
	     Return a caller-owned integer for the memory type.

     memstat_set_caller_uint64()
	     Set a caller-owned integer for the memory type.

     memstat_get_zonefree()
	     If the memory allocator supports a multi-level allocation struc‐
	     ture, return the number of cached items in the zone.  These items
	     will be in a fully constructed state available for immediate use.

     memstat_get_kegfree()
	     If the memory allocator supports a multi-level allocation struc‐
	     ture, return the number of cached items in the keg.  These items
	     may be in a partially constructed state, and may require further
	     processing before they can be made available for use.

     memstat_get_percpu_memalloced()
	     If the memory allocator supports per-CPU statistics, return the
	     number of bytes of memory allocated for the memory type on the
	     CPU over its lifetime.

     memstat_get_percpu_memfreed()
	     If the memory allocator supports per-CPU statistics, return the
	     number of bytes of memory freed from the memory type on the CPU
	     over its lifetime.

     memstat_get_percpu_numallocs()
	     If the memory allocator supports per-CPU statistics, return the
	     number of allocations for the memory type on the CPU over its
	     lifetime.

     memstat_get_percpu_numfrees()
	     If the memory allocator supports per-CPU statistics, return the
	     number of frees for the memory type on the CPU over its lifetime.

     memstat_get_percpu_sizemask()
	     If the memory allocator supports variable size memory allocation
	     and per-CPU statistics, return the size bitmask for the memory
	     type on the CPU.

     memstat_get_percpu_caller_pointer()
	     Return a caller-owned per-CPU pointer for the memory type.

     memstat_set_percpu_caller_pointer()
	     Set a caller-owned per-CPU pointer for the memory type.

     memstat_get_percpu_caller_uint64()
	     Return a caller-owned per-CPU integer for the memory type.

     memsttat_set_percpu_caller_uint64()
	     Set a caller-owned per-CPU integer for the memory type.

     memstat_get_percpu_free()
	     If the memory allocator supports a per-CPU cache, return the num‐
	     ber of free items in the per-CPU cache of the designated CPU.

RETURN VALUES
     libmemstat functions fall into three categories: functions returning a
     pointer to an object, functions returning an integer return value, and
     functions implementing accessor methods returning data from a struct
     memory_type.

     Functions returning a pointer to an object will generally return NULL on
     failure.  memstat_mtl_alloc() will return an error value via errno, which
     will consist of the value ENOMEM.	Functions memstat_mtl_first(),
     memstat_mtl_next(), and memstat_mtl_find() will return NULL when there is
     no entry or match in the list; however, this is not considered a failure
     mode and no error value is available.

     Functions returning an integer success value will return 0 on success, or
     -1 on failure.  If a failure is returned, the list error access method,
     memstat_mtl_geterror(), may be used to retrieve the error state.  The
     string representation of the error may be retrieved using
     memstat_strerror().  Possible error values are:

     MEMSTAT_ERROR_UNDEFINED	  Undefined error.  Occurs if
				  memstat_mtl_geterror() is called on a list
				  before an error associated with the list has
				  occurred.

     MEMSTAT_ERROR_NOMEMORY	  Insufficient memory.	Occurs if library
				  calls to malloc(3) fail, or if a system call
				  to retrieve kernel statistics fails with
				  ENOMEM.

     MEMSTAT_ERROR_VERSION	  Returned if the current version of
				  libmemstat is unable to interpret the sta‐
				  tistics data returned by the kernel due to
				  an explicit version mismatch, or to differ‐
				  ences in data structures that cannot be rec‐
				  onciled.

     MEMSTAT_ERROR_PERMISSION	  Returned if a statistics source returns
				  errno values of EACCES or EPERM.

     MEMSTAT_ERROR_TOOMANYCPUS	  Returned if the compile-time limit on the
				  number of CPUs in libmemstat is lower than
				  the number of CPUs returned by a statistics
				  data source.

     MEMSTAT_ERROR_DATAERROR	  Returned if libmemstat is unable to inter‐
				  pret statistics data returned by the data
				  source, even though there does not appear to
				  be a version problem.

     MEMSTAT_ERROR_KVM		  Returned if libmemstat experiences an error
				  while using kvm(3) interfaces to query sta‐
				  tistics data.	 Use kvm_geterr(3) to retrieve
				  the error.

     MEMSTAT_ERROR_KVM_NOSYMBOL	  Returned if libmemstat is unable to read a
				  required symbol from the kernel being oper‐
				  ated on.

     MEMSTAT_ERROR_KVM_SHORTREAD  Returned if libmemstat attempts to read data
				  from a live memory image or kernel core dump
				  and insufficient data is returned.

     Finally, functions returning data from a struct memory_type pointer are
     not permitted to fail, and directly return either a statistic or pointer
     to a string.

EXAMPLES
     Create a memory type list, query the uma(9) memory allocator for avail‐
     able statistics, and print out the number of allocations performed by the
     mbuf zone.

	   struct memory_type_list *mtlp;
	   struct memory_type *mtp;
	   uint64_t mbuf_count;

	   mtlp = memstat_mtl_alloc();
	   if (mtlp == NULL)
	       err(-1, "memstat_mtl_alloc");
	   if (memstat_sysctl_uma(mtlp, 0) < 0)
	       err(-1, "memstat_sysctl_uma");
	   mtp = memstat_mtl_find(mtlp, ALLOCATOR_UMA, "mbuf");
	   if (mtp == NULL)
	       errx(-1, "memstat_mtl_find: mbuf not found");
	   mbuf_count = memstat_get_count(mtp);
	   memstat_mtl_free(mtlp);

	   printf("mbufs: %llu\n", (unsigned long long)mbuf_count);

SEE ALSO
     malloc(9), uma(9)

HISTORY
     The libmemstat library appeared in FreeBSD 6.0.

AUTHORS
     The kernel memory allocator changes necessary to support a general pur‐
     pose monitoring library, along with the library, were written by Robert
     Watson ⟨rwatson@FreeBSD.org⟩.

BUGS
     There are memory allocators in the kernel, such as the VM page allocator
     and sf_buf allocator, which are not currently supported by libmemstat.

     Once a memory type is present on a memory type list, it will not be
     removed even if the kernel no longer presents information on the type via
     its monitoring interfaces.	 In order to flush removed memory types, it is
     necessary to free the entire list and allocate a new one.

BSD				 June 27, 2005				   BSD
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