POOL_CACHE(9) BSD Kernel Developer's Manual POOL_CACHE(9)NAME
pool_cache, pool_cache_init, pool_cache_destroy, pool_cache_get_paddr,
pool_cache_get, pool_cache_put_paddr, pool_cache_put,
pool_cache_destruct_object, pool_cache_invalidate, pool_cache_sethiwat,
pool_cache_setlowat, pool_cache_sethardlimit — resource-pool cache man‐
ager
SYNOPSIS
#include <sys/pool.h>
pool_cache_t
pool_cache_init(size_t size, u_int align, u_int align_offset, int flags,
const char *name, struct pool_allocator *palloc, int ipl,
int (*ctor)(void *, void *, int), void (*dtor)(void *, void *),
void *arg);
void
pool_cache_destroy(pool_cache_t pc);
void *
pool_cache_get_paddr(pool_cache_t pc, int flags, paddr_t *pap);
void *
pool_cache_get(pool_cache_t pc, int flags);
void
pool_cache_put_paddr(pool_cache_t pc, void *object, paddr_t pa);
void
pool_cache_put(pool_cache_t pc, void *object);
void
pool_cache_destruct_object(pool_cache_t pc, void *object);
void
pool_cache_invalidate(pool_cache_t pc);
void
pool_cache_sethiwat(pool_cache_t pc, int nitems);
void
pool_cache_setlowat(pool_cache_t pc, int nitems);
void
pool_cache_sethardlimit(pool_cache_t pc, int nitems,
const char *warnmess, int ratecap);
DESCRIPTION
These utility routines provide management of pools of fixed-sized areas
of memory. Resource pools set aside an amount of memory for exclusive
use by the resource pool owner. This can be used by applications to
guarantee the availability of a minimum amount of memory needed to con‐
tinue operation independent of the memory resources currently available
from the system-wide memory allocator.
pool_cache follows the pool(9) API closely and offers routines that are
functionally equivalent to their pool(9) counterparts. In addition,
pool_cache provides object management functions used to manipulate
objects allocated from the pool. It also maintains global and per-CPU
caches, both levels of cache work together to allow for low overhead
allocation and release of objects, and improved L1/L2/L3 hardware cache
locality in multiprocessor systems.
FUNCTIONS
pool_cache_init(size, align, align_offset, flags, name, palloc, ipl,
ctor, dtor, arg)
Allocate and initialize a pool cache. The arguments are:
size
Specifies the size of the memory items managed by the
pool.
align
Specifies the memory address alignment of the items
returned by pool_cache_get(). This argument must be a
power of two. If zero, the alignment defaults to an
architecture-specific natural alignment.
align_offset
The offset within an item to which the align parameter
applies.
flags
Should be set to zero or PR_NOTOUCH. If PR_NOTOUCH is
given, free items are never used to keep internal state so
that the pool can be used for non memory backed objects.
name
The name used to identify the object in diagnostic output.
palloc
Should be typically be set to NULL, instructing
pool_cache_init() to select an appropriate back-end allo‐
cator. Alternate allocators can be used to partition
space from arbitrary sources. Use of alternate allocators
is not documented here as it is not a stable, endorsed
part of the API.
ipl
Specifies an interrupt priority level that will block all
interrupt handlers that could potentially access the pool.
The pool_cache facility provides its own synchronization.
The users of any given pool_cache need not provide addi‐
tional synchronization for access to it.
ctor
Specifies a constructor used to initialize newly allocated
objects. If no constructor is required, specify NULL.
The first argument to ctor is arg, the second is the new
object, and the third is flags.
dtor
Specifies a destructor used to destroy cached objects
prior to their release to backing store. If no destructor
is required, specify NULL. The first argument to dtor is
arg, and the second is the object.
arg
This value of this argument will be passed to both the
constructor and destructor routines.
pool_cache_destroy(pc)
Destroy a pool cache pc. All other access to the cache must be
stopped before this call can be made.
pool_cache_get_paddr(pc, flags, pap)
Get an object from a pool cache pc. If pap is not NULL, physi‐
cal address of the object or POOL_PADDR_INVALID will be returned
via it. flags will be passed to pool_get() function of the
backing pool(9) and the object constructor specified when the
pool cache is created by pool_cache_init().
pool_cache_get(pc, flags)
pool_cache_get() is the same as pool_cache_get_paddr() with NULL
pap argument. It's implemented as a macro.
pool_cache_put_paddr(pc, object, pa)
Put an object object back to the pool cache pc. pa should be
physical address of the object object or POOL_PADDR_INVALID.
pp. If the number of available items in the backing pool
exceeds the maximum pool size set by pool_cache_sethiwat() and
there are no outstanding requests for pool items, the excess
items will be returned to the system.
pool_cache_put(pc, object)
pool_cache_put() is the same as pool_cache_put_paddr() with
POOL_PADDR_INVALID pa argument. It's implemented as a macro.
pool_cache_destruct_object(pc, object)
Force destruction of an object object and release it back into
the pool.
pool_cache_invalidate(pc)
Invalidate a pool cache pc. All objects in the cache will be
destructed and freed back to the pool backing the cache. For
pool caches that vend constructed objects, consumers of this API
must take care to provide proper synchronization between the
input to the constructor and cache invalidation.
pool_cache_sethiwat(pc, nitems)
A pool will attempt to increase its resource usage to keep up
with the demand for its items. Conversely, it will return
unused memory to the system should the number of accumulated
unused items in the pool exceed a programmable limit. The lim‐
its for the minimum and maximum number of items which a pool
should keep at hand are known as the high and low watermarks.
The function pool_cache_sethiwat() sets the backing pool's high
water mark. As items are returned and the total number of pages
in the pool is larger than the maximum set by this function, any
completely unused pages are released immediately. If this func‐
tion is not used to specify a maximum number of items, the pages
will remain associated with the pool until the system runs low
on memory, at which point the VM system will try to reclaim
unused pages.
pool_cache_setlowat(pc, nitems)
Set the minimum number of items to keep in the pool. The number
pages in the pool will not decrease below the required value to
accommodate the minimum number of items specified by this func‐
tion.
pool_cache_sethardlimit(pc, nitems, warnmess, ratecap)
Set the hard limit for the backing pool(9) to nitems. When the
hard limit is reached, the warning message warnmess will be
logged. ratecap represents the minimal interval (in seconds)
after which another warning message is issued when the pool hits
its hard limit again.
CODE REFERENCES
The pool_cache subsystem is implemented within the file
sys/kern/subr_pool.c.
SEE ALSOintro(9), kmem(9), memoryallocators(9), percpu(9), pool(9)CAVEATSpool_cache_invalidate() only affects objects safely accessible by the
local CPU. On multiprocessor systems this function should be called by
each CPU to invalidate their local caches. See xcall(9) for an interface
to schedule the execution of arbitrary functions to any other CPU.
BSD November 15, 2011 BSD
