freebsd-dev/lib/libmemstat/libmemstat.3

.\" 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"
.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_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.
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 .
.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.