svcadm(8)을 검색하려면 섹션에서 8 을 선택하고, 맨 페이지 이름에 svcadm을 입력하고 검색을 누른다.
uma_zcreate(9)
ZONE(9) BSD Kernel Developer's Manual ZONE(9)
NAME
uma_zcreate, uma_zalloc, uma_zalloc_arg, uma_zalloc_domain, uma_zfree,
uma_zfree_arg, uma_zfree_domain, uma_zdestroy, uma_zone_set_max,
uma_zone_get_max, uma_zone_get_cur, uma_zone_set_warning,
uma_zone_set_maxaction — zone allocator
SYNOPSIS
#include <sys/param.h>
#include <sys/queue.h>
#include <vm/uma.h>
uma_zone_t
uma_zcreate(char *name, int size, uma_ctor ctor, uma_dtor dtor,
uma_init uminit, uma_fini fini, int align, uint16_t flags);
void *
uma_zalloc(uma_zone_t zone, int flags);
void *
uma_zalloc_arg(uma_zone_t zone, void *arg, int flags);
void *
uma_zalloc_domain(uma_zone_t zone, void *arg, int domain, int flags);
void
uma_zfree(uma_zone_t zone, void *item);
void
uma_zfree_arg(uma_zone_t zone, void *item, void *arg);
void
uma_zfree_domain(uma_zone_t zone, void *item, void *arg);
void
uma_zdestroy(uma_zone_t zone);
int
uma_zone_set_max(uma_zone_t zone, int nitems);
int
uma_zone_get_max(uma_zone_t zone);
int
uma_zone_get_cur(uma_zone_t zone);
void
uma_zone_set_warning(uma_zone_t zone, const char *warning);
void
uma_zone_set_maxaction(uma_zone_t zone, void (*maxaction)(uma_zone_t));
#include <sys/sysctl.h>
SYSCTL_UMA_MAX(parent, nbr, name, access, zone, descr);
SYSCTL_ADD_UMA_MAX(ctx, parent, nbr, name, access, zone, descr);
SYSCTL_UMA_CUR(parent, nbr, name, access, zone, descr);
SYSCTL_ADD_UMA_CUR(ctx, parent, nbr, name, access, zone, descr);
DESCRIPTION
The zone allocator provides an efficient interface for managing dynami‐
cally-sized collections of items of identical size. The zone allocator
can work with preallocated zones as well as with runtime-allocated ones,
and is therefore available much earlier in the boot process than other
memory management routines. The zone allocator provides per-cpu alloca‐
tion caches with linear scalability on SMP systems as well as round-robin
and first-touch policies for NUMA systems.
A zone is an extensible collection of items of identical size. The zone
allocator keeps track of which items are in use and which are not, and
provides functions for allocating items from the zone and for releasing
them back (which makes them available for later use).
After the first allocation of an item, it will have been cleared to
zeroes, however subsequent allocations will retain the contents as of the
last free.
The uma_zcreate() function creates a new zone from which items may then
be allocated from. The name argument is a text name of the zone for
debugging and stats; this memory should not be freed until the zone has
been deallocated.
The ctor and dtor arguments are callback functions that are called by the
uma subsystem at the time of the call to uma_zalloc() and uma_zfree()
respectively. Their purpose is to provide hooks for initializing or
destroying things that need to be done at the time of the allocation or
release of a resource. A good usage for the ctor and dtor callbacks
might be to adjust a global count of the number of objects allocated.
The uminit and fini arguments are used to optimize the allocation of
objects from the zone. They are called by the uma subsystem whenever it
needs to allocate or free several items to satisfy requests or memory
pressure. A good use for the uminit and fini callbacks might be to ini‐
tialize and destroy mutexes contained within the object. This would
allow one to re-use already initialized mutexes when an object is
returned from the uma subsystem's object cache. They are not called on
each call to uma_zalloc() and uma_zfree() but rather in a batch mode on
several objects.
The flags argument of the uma_zcreate() is a subset of the following
flags:
UMA_ZONE_NOFREE
Slabs of the zone are never returned back to VM.
UMA_ZONE_NODUMP
Pages belonging to the zone will not be included into mini-dumps.
UMA_ZONE_PCPU
An allocation from zone would have mp_ncpu shadow copies, that are
privately assigned to CPUs. A CPU can address its private copy
using base allocation address plus multiple of current CPU id and
sizeof(struct pcpu):
foo_zone = uma_zcreate(..., UMA_ZONE_PCPU);
...
foo_base = uma_zalloc(foo_zone, ...);
...
critical_enter();
foo_pcpu = (foo_t *)zpcpu_get(foo_base);
/* do something with foo_pcpu */
critical_exit();
UMA_ZONE_OFFPAGE
By default book-keeping of items within a slab is done in the slab
page itself. This flag explicitly tells subsystem that book-keeping
structure should be allocated separately from special internal zone.
This flag requires either UMA_ZONE_VTOSLAB or UMA_ZONE_HASH, since
subsystem requires a mechanism to find a book-keeping structure to
an item being freed. The subsystem may choose to prefer offpage
book-keeping for certain zones implicitly.
UMA_ZONE_ZINIT
The zone will have its uma_init method set to internal method that
initializes a new allocated slab to all zeros. Do not mistake
uma_init method with uma_ctor. A zone with UMA_ZONE_ZINIT flag
would not return zeroed memory on every uma_zalloc().
UMA_ZONE_HASH
The zone should use an internal hash table to find slab book-keeping
structure where an allocation being freed belongs to.
UMA_ZONE_VTOSLAB
The zone should use special field of vm_page_t to find slab book-
keeping structure where an allocation being freed belongs to.
UMA_ZONE_MALLOC
The zone is for the malloc(9) subsystem.
UMA_ZONE_VM
The zone is for the VM subsystem.
UMA_ZONE_NUMA
The zone should use a first-touch NUMA policy rather than the round-
robin default. Callers that do not free memory on the same domain it
is allocated from will cause mixing in per-cpu caches. See numa(9)
for more details.
To allocate an item from a zone, simply call uma_zalloc() with a pointer
to that zone and set the flags argument to selected flags as documented
in malloc(9). It will return a pointer to an item if successful, or NULL
in the rare case where all items in the zone are in use and the allocator
is unable to grow the zone and M_NOWAIT is specified.
Items are released back to the zone from which they were allocated by
calling uma_zfree() with a pointer to the zone and a pointer to the item.
If item is NULL, then uma_zfree() does nothing.
The variations uma_zalloc_arg() and uma_zfree_arg() allow callers to
specify an argument for the ctor and dtor functions, respectively. The
uma_zalloc_domain() function allows callers to specify a fixed numa(9)
domain to allocate from. This uses a guaranteed but slow path in the
allocator which reduces concurrency. The uma_zfree_domain() function
should be used to return memory allocated in this fashion. This function
infers the domain from the pointer and does not require it as an argu‐
ment.
Created zones, which are empty, can be destroyed using uma_zdestroy(),
freeing all memory that was allocated for the zone. All items allocated
from the zone with uma_zalloc() must have been freed with uma_zfree()
before.
The uma_zone_set_max() function limits the number of items (and therefore
memory) that can be allocated to zone. The nitems argument specifies the
requested upper limit number of items. The effective limit is returned
to the caller, as it may end up being higher than requested due to the
implementation rounding up to ensure all memory pages allocated to the
zone are utilised to capacity. The limit applies to the total number of
items in the zone, which includes allocated items, free items and free
items in the per-cpu caches. On systems with more than one CPU it may
not be possible to allocate the specified number of items even when there
is no shortage of memory, because all of the remaining free items may be
in the caches of the other CPUs when the limit is hit.
The uma_zone_get_max() function returns the effective upper limit number
of items for a zone.
The uma_zone_get_cur() function returns the approximate current occupancy
of the zone. The returned value is approximate because appropriate syn‐
chronisation to determine an exact value is not performed by the imple‐
mentation. This ensures low overhead at the expense of potentially stale
data being used in the calculation.
The uma_zone_set_warning() function sets a warning that will be printed
on the system console when the given zone becomes full and fails to allo‐
cate an item. The warning will be printed no more often than every five
minutes. Warnings can be turned off globally by setting the
vm.zone_warnings sysctl tunable to 0.
The uma_zone_set_maxaction() function sets a function that will be called
when the given zone becomes full and fails to allocate an item. The
function will be called with the zone locked. Also, the function that
called the allocation function may have held additional locks. There‐
fore, this function should do very little work (similar to a signal han‐
dler).
The SYSCTL_UMA_MAX(parent, nbr, name, access, zone, descr) macro declares
a static sysctl oid that exports the effective upper limit number of
items for a zone. The zone argument should be a pointer to uma_zone_t.
A read of the oid returns value obtained through uma_zone_get_max(). A
write to the oid sets new value via uma_zone_set_max(). The
SYSCTL_ADD_UMA_MAX(ctx, parent, nbr, name, access, zone, descr) macro is
provided to create this type of oid dynamically.
The SYSCTL_UMA_CUR(parent, nbr, name, access, zone, descr) macro declares
a static read-only sysctl oid that exports the approximate current occu‐
pancy of the zone. The zone argument should be a pointer to uma_zone_t.
A read of the oid returns value obtained through uma_zone_get_cur(). The
SYSCTL_ADD_UMA_CUR(ctx, parent, nbr, name, zone, descr) macro is provided
to create this type of oid dynamically.
RETURN VALUES
The uma_zalloc() function returns a pointer to an item, or NULL if the
zone ran out of unused items and M_NOWAIT was specified.
IMPLEMENTATION NOTES
The memory that these allocation calls return is not executable. The
uma_zalloc() function does not support the M_EXEC flag to allocate exe‐
cutable memory. Not all platforms enforce a distinction between exe‐
cutable and non-executable memory.
SEE ALSO
malloc(9)
HISTORY
The zone allocator first appeared in FreeBSD 3.0. It was radically
changed in FreeBSD 5.0 to function as a slab allocator.
AUTHORS
The zone allocator was written by John S. Dyson. The zone allocator was
rewritten in large parts by Jeff Roberson <jeff@FreeBSD.org> to function
as a slab allocator.
This manual page was written by Dag-Erling Smørgrav <des@FreeBSD.org>.
Changes for UMA by Jeroen Ruigrok van der Werven <asmodai@FreeBSD.org>.
BSD June 13, 2018 BSD