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POOL_CACHE(9) NetBSD Kernel Developer's Manual POOL_CACHE(9)
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by Kimmo Suominen.
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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-
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 *),
pool_cache_get_paddr(pool_cache_t pc, int flags, paddr_t *pap);
pool_cache_get(pool_cache_t pc, int flags);
pool_cache_put_paddr(pool_cache_t pc, void *object, paddr_t pa);
pool_cache_put(pool_cache_t pc, void *object);
pool_cache_destruct_object(pool_cache_t pc, void *object);
pool_cache_sethiwat(pool_cache_t pc, int n);
pool_cache_setlowat(pool_cache_t pc, int n);
pool_cache_sethardlimit(pool_cache_t pc, int n, const char *warnmess,
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.
pool_cache_init(size, align, align_offset, flags, name, palloc, ipl,
ctor, dtor, arg)
Allocate and initialize a pool cache. The arguments are:
Specifies the size of the memory items managed by the
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.
The offset within an item to which the align parameter
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.
The name used to identify the object in diagnostic output.
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.
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.
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.
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.
This value of this argument will be passed to both the
constructor and destructor routines.
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() 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. 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() is the same as pool_cache_put_paddr() with
POOL_PADDR_INVALID pa argument. It's implemented as a macro.
Force destruction of an object object and release it back into
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.
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
free items in the pool exceed a programmable limit. The limits
for the minimum and maximum number of free items which a pool
should try to keep available are known as the high and low
The function pool_cache_sethiwat() sets the backing pool's high
water mark. As items are freed and the number of free items 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
Set the minimum number of free items to try to keep in the pool.
When the number of free items in the pool drops below this
threshold, a non-blocking attempt is made to allocate memory for
more items. The number of free items is not guaranteed to
remain above this threshold.
pool_cache_sethardlimit(pc, n, warnmess, ratecap)
Set the maximum number of total items (both free and allocated)
for the backing pool(9) to n. 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.
Set the minimum number of total items (both free and allocated)
for the backing pool(9) to n.
The pool_cache subsystem is implemented within the file
intro(9), kmem(9), memoryallocators(9), percpu(9), pool(9)
NetBSD 9.99 April 12, 2020 NetBSD 9.99