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
     manager

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 exclu-
     sive use by the resource pool owner.  This can be used by applications to guarantee the availability of a minimum amount of memory needed to
     continue 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 allocator.  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 additional synchro-
		    nization 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, physical 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 out-
	      standing 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 mem-
	      ory to the system should the number of accumulated unused items in the pool exceed a programmable limit.	The limits 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 function 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 function.

     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 ALSO

     intro(9), kmem(9), memoryallocators(9), percpu(9), pool(9)

CAVEATS

     pool_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