.\" Copyright (c) 2005 Robert N. M. Watson
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.Dd June 27, 2005
.Os
.Dt LIBMEMSTAT 3
.Sh NAME
.Nm libmemstat
.Nd "library interface to retrieve kernel memory allocator statistics"
.Sh LIBRARY
.Lb libmemstat
.Sh SYNOPSIS
.In sys/types.h
.In memstat.h
.Ss Memory Type List Management Functions
.Ft struct memory_type_list *
.Fn memstat_mtl_alloc "void"
.Ft struct memory_type *
.Fn memstat_mtl_first "struct memory_type_list *list"
.Ft struct memory_type *
.Fn memstat_mtl_next "struct memory_type *mtp"
.Ft struct memory_type *
.Fn memstat_mtl_find "struct memory_type_list *list" "int allocator" "const char *name"
.Ft void
.Fn memstat_mtl_free "struct memory_type_list *list"
.Ft int
.Fn memstat_mtl_geterror "struct memory_type_list *list"
.Ss Allocator Query Functions
.Ft int
.Fn memstat_sysctl_all "struct memory_type_list *list" "int flags"
.Ft int
.Fn memstat_sysctl_malloc "struct memory_type_list *list" "int flags"
.Ft int
.Fn memstat_sysctl_uma "struct memory_type_list *list" "int flags"
.Ss Memory Type Accessor Methods
.Ft const char *
.Fn memstat_get_name "const struct memory_type *mtp"
.Ft int
.Fn memstat_get_allocator "const struct memory_type *mtp"
.Ft uint64_t
.Fn memstat_get_countlimit "const struct memory_type *mtp"
.Ft uint64_t
.Fn memstat_get_byteslimit "const struct memory_type *mtp"
.Ft uint64_t
.Fn memstat_get_sizemask "const struct memory_type *mtp"
.Ft uint64_t
.Fn memstat_get_size "const struct memory_type *mtp"
.Ft uint64_t
.Fn memstat_get_memalloced "const struct memory_type *mtp"
.Ft uint64_t
.Fn memstat_get_memfreed "const struct memory_type *mtp"
.Ft uint64_t
.Fn memstat_get_numallocs "const struct memory_type *mtp"
.Ft uint64_t
.Fn memstat_get_numfrees "const struct memory_type *mtp"
.Ft uint64_t
.Fn memstat_get_bytes "const struct memory_type *mtp"
.Ft uint64_t
.Fn memstat_get_count "const struct memory_type *mtp"
.Ft uint64_t
.Fn memstat_get_free "const struct memory_type *mtp"
.Ft uint64_t
.Fn memstat_get_failures "const struct memory_type *mtp"
.Ft void *
.Fn memstat_get_caller_pointer "const struct memory_type *mtp" "int index"
.Ft void
.Fn memstat_set_caller_pointer "struct memory_type *mtp" "int index" "void *value"
.Ft uint64_t
.Fn memstat_get_caller_uint64 "const struct memory_type *mtp" "int index"
.Ft void
.Fn memstat_set_caller_uint64 "struct memory_type *mtp" "int index" "uint64_t value"
.Ft uint64_t
.Fn memstat_get_zonefree "const struct memory_type *mtp"
.Ft uint64_t
.Fn memstat_get_kegfree "const struct memory_type *mtp"
.Ft uint64_t
.Fn memstat_get_percpu_memalloced "const struct memory_type *mtp" "int cpu"
.Ft uint64_t
.Fn memstat_get_percpu_memfreed "const struct memory_type *mtp" "int cpu"
.Ft uint64_t
.Fn memstat_get_percpu_numallocs "const struct memory_type *mtp" "int cpu"
.Ft uint64_t
.Fn memstat_get_percpu_numfrees "const struct memory_type *mtp" "int cpu"
.Ft uint64_t
.Fn memstat_get_percpu_sizemask "const struct memory_type *mtp" "int cpu"
.Ft void *
.Fn memstat_get_percpu_caller_pointer "const struct memory_type *mtp" "int cpu" "int index"
.Ft void
.Fn memstat_set_percpu_caller_pointer "struct memory_type *mtp" "int cpu" "int index" "void *value"
.Ft uint64_t
.Fn memstat_get_percpu_caller_uint64 "const struct memory_type *mtp" "int cpu" "int index"
.Ft void
.Fn memstat_set_percpu_caller_uint64 "struct memory_type *mtp" "int cpu" "int index" "uint64_t value"
.Ft uint64_t
.Fn memstat_get_percpu_free "const struct memory_type *mtp" "int cpu"
.Sh DESCRIPTION
.Nm
provides an interface to retrieve kernel memory allocator statistics, 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.
.Nm
supports both retrieving a single statistics snapshot, as well as
incrementally updating statistics for long-term monitoring.
.Pp
.Nm
describes each memory type using a
.Vt struct memory_type ,
an opaque memory type accessed by the application using accessor functions
in the library.
.Nm
returns and updates chains of
.Vt struct memory_type
via a
.Vt struct memory_type_list ,
which will be allocated by calling
.Fn memstat_mtl_alloc ,
and freed on completion using
.Fn memstat_mtl_free .
Lists of memory types are populated via calls that query the kernel for
statistics information; currently:
.Fn memstat_sysctl_all ,
.Fn memstat_sysctl_uma ,
and
.Fn memstat_sysctl_malloc .
Repeated calls will incrementally update the list of memory types, permitting
tracking over time without recreating all list state.
If an error is detected during a query call, error condition information may
be retrieved using
.Fn memstat_mtl_geterror .
.Pp
Freeing the list will free all memory type data in the list, and so
invalidates any outstanding pointers to entries in the list.
.Vt struct memory_type
entries in the list may be iterated over using
.Fn memstat_mtl_first
and
.fn memstat_mtl_next ,
which respectively return the first entry in a list, and the next entry in a
list.
.Fn memstat_mtl_find ,
which will return a pointer to the first entry matching the passed
parameters.
.Pp
A series of accessor methods is provided to access fields of the structure,
including retrieving statistics and properties, as well as setting of caller
owned fields.
Direct application access to the data structure fields is not supported.
.Ss Library memory_type Fields
Each
.Vt struct memory_type
holds a description of the memory type, including its name and the allocator
it is managed by, as well as current statistics 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 allocations, is available only for specific
allocators.
.Ss Caller memory_type Fields
.Vt 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 provided with each
.Vt struct memory_type
in the form of an array of pointers and integers.
The array entries are accessed via the
.Fa index
argument to the get and set accessor methods.
Possible values of
.Fa index
range between
.Dv 0
and
.Dv MEMSTAT_MAXCALLER .
.Pp
Caller-owned fields are initialized to
.Dv 0
or
.Dv NULL
when a new
.Vt struct memory_type
is allocated and attached to a memory type list; these fields retain their
values across queries that update library-owned fields.
.Ss Allocator Types
Currently,
.Nm
supports two kernel allocators:
.Dv ALLOCATOR_UMA
for
.Xr uma 9 ,
and
.Dv ALLOCATOR_MALLOC
for
.Xr malloc 9 .
These values may be passed to
.Fn memstat_mtl_find ,
and will be returned by
.Fn memstat_get_allocator .
Two additional constants in the allocator name space are defined:
.Dv ALLOCATOR_UNKNOWN ,
which will only be returned as a result of a library error, and
.Dv ALLOCATOR_ANY ,
which can be used to specify that returning types matching any allocator is
permittible from
.Fn memstat_mtl_find .
.Ss Access Method List
The following accessor methods are defined, of which some will be valid for
a given memory type:
.Pp
.Bl -tag -width "memstat_get_name" -compact -offset wee
.It memstat_get_name
Return a pointer to the name of the memory type.
Memory for the name is owned by
.Nm
and will be valid through a call to
.Fn 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.
.It memstat_get_allocator
Return an integer identifier for the memory allocator that owns the memory
type.
.It memstat_get_countlimit
If the memory type has an administrative limit on the number of simultaneous
allocations, return it.
.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 memory type, return it.
.It memstat_get_sizemask
If the memory type supports variable allocation sizes, return a bitmask of
sizes allocated for the memory type.
.It memstat_get_size
If the memory type supports a fixed allocation size, return that size.
.It memstat_get_memalloced
Return the total number of bytes allocated for the memory type over its
lifetime.
.It memstat_get_memfreed
Return the total number of bytes freed for the memory type over its lifetime.
.It memstat_get_numallocs
Return the total number of allocations for the memory type over its lifetime.
.It memstat_get_numfrees
Return the total number of frees for the memory type over its lifetime.
.It memstat_get_bytes
Return the current number of bytes allocated to the memory type.
.It memstat_get_count
Return the current number of allocations for the memory type.
.It memstat_get_free
If the memory allocator supports a cache, return the number of items in the
cache.
.It memstat_get_failures
If the memory allocator and type permit allocation failures, return the
number of allocation failures measured.
.It memstat_get_caller_pointer
Return a caller-owned pointer for the memory type.
.It memstat_set_caller_pointer
Set a caller-owned pointer for the memory type.
.It memstat_get_caller_uint64
Return a caller-owned integer for the memory type.
.It memstat_set_caller_uint64
Set a caller-owned integer for the memory type.
.It memstat_get_zonefree
If the memory allocator supports a multi-level allocation structure, return
the number of cached items in the zone.
These items will be in a fully constructed state available for immediate
use.
.It memstat_get_kegfree
If the memory allocator supports a multi-level allocation structure, 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.
.It 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.
.It 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.
.It 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.
.It 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.
.It 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.
.It memstat_get_percpu_caller_pointer
Return a caller-owned per-CPU pointer for the memory type.
.It memstat_set_percpu_caller_pointer
Set a caller-owned per-CPU pointer for the memory type.
.It memstat_get_percpu_caller_uint64
Return a caller-owned per-CPU integer for the memory type.
.It memsttat_set_percpu_caller_uint64
Set a caller-owned per-CPU integer for the memory type.
.It memstat_get_percpu_free
If the memory allocator supports a per-CPU cache, return the number of free
items in the per-CPU cache of the designated CPU.
.El
.Sh RETURN VALUES
.Nm
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
.Vt struct memory_type .
.Pp
Functions returning a pointer to an object will generally return
.Dv NULL
on failure.
.Fn memstat_mtl_alloc
will return an error value via
.Va errno ,
which will consist of the value
.Dv ENOMEM .
Functions
.Fn memstat_mtl_first ,
.Fn memstat_mtl_next ,
and
.Fn memstat_mtl_find
will return
.Dv 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.
.Pp
Functions returning a integer success valuye will return
.Dv 0
on success, or
.Dv -1
on failure.
If a failure is returned, the list error access method,
.Fn memstat_mtl_geterror ,
may be used to retrieve the error state.  Possible error values are:
.Pp
.Bl -tag -width "MEMSTAT_ERROR_TOOMANYCPUS" -compact -offset wee
.It Dv MEMSTAT_ERROR_UNDEFINED
Undefined error.  Occurs if
.Fn memstat_mtl_geterror
is called on a list before an error associated with the list has occurred.
.It Dv MEMSTAT_ERROR_NOMEMORY
Insufficient memory.  Occurs if library calls to
.Xr malloc 3
fail, or if a system call to retrieve kernel statistics fails with
.Er ENOMEM .
.It Dv MEMSTAT_ERROR_VERSION
Returned if the current version of
.Nm
is unable to interpret the statistics data returned by the kernel due to an
explicit version mismatch, or to differences in data structures that cannot
be reconciled.
.It Dv MEMSTAT_ERROR_PERMISSION
Returned if a statistics source returns
.Va errno
values of
.Dv EACCES
or
.Dv EPERM .
.It Dv MEMSTAT_ERROR_TOOMANYCPUS
Returned if the compile-time limit on the number of CPUs in
.Nm
is lower than the number of CPUs returned by a statistics data source.
.It Dv MEMSTAT_ERROR_DATAERROR
Returned if
.Nm
is unable to interpret statistics data returned by the data source, even
though there does not appear to be a version problem.
.El
.Pp
Finally, functions returning data from a
.Dt struct memory_type
pointer are not permitted to fail, and directly return either a statistic
or pointer to a string.
.Sh EXAMPLES
Create a memory type list, query the
.Xr uma 9
memory allocator for available statistics, and print out the number of
allocations performed by the
.Dv Mbuf
zone.
.Bd -literal -offset indent
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);
.Ed
.Sh SEE ALSO
.Xr malloc 9 ,
.Xr uma 9
.Sh HISTORY
The
.Nm memstat
library appeared in
.Fx 6.0 .
.Sh AUTHORS
The kernel memory allocator changes necessary to support a general purpose
monitoring library, along with the library, were written by
.An Robert Watson Aq rwatson@FreeBSD.org
.Sh BUGS
.Nm
cannot yet extract statistics from kernel core dumps, although this should be
straight forward to implement.
.Pp
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.