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NetBSD 6.1.5 - man page for pool_cache_setlowat (netbsd section 9)

POOL_CACHE(9)			  BSD Kernel Developer's Manual 		    POOL_CACHE(9)

     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

     #include <sys/pool.h>

     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);

     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);

     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_invalidate(pool_cache_t pc);

     pool_cache_sethiwat(pool_cache_t pc, int nitems);

     pool_cache_setlowat(pool_cache_t pc, int nitems);

     pool_cache_sethardlimit(pool_cache_t pc, int nitems, const char *warnmess, int ratecap);

     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 continue operation independent of the memory resources currently available from the sys-
     tem-wide memory allocator.

     pool_cache follows the pool(9) API closely and offers routines that are functionally equiva-
     lent 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 pool.


		    Specifies the memory address alignment of the items returned by
		    pool_cache_get().  This argument must be a power of two.  If zero, the align-
		    ment defaults to an architecture-specific natural alignment.


		    The offset within an item to which the align parameter applies.


		    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 allocator.	Alternate allocators can be used to par-
		    tition space from arbitrary sources.  Use of alternate allocators is not doc-
		    umented 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
		    additional 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, 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 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.


	      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 num-
	      ber 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 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 mini-
	      mal interval (in seconds) after which another warning message is issued when the
	      pool hits its hard limit again.

     The pool_cache subsystem is implemented within the file sys/kern/subr_pool.c.

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

     pool_cache_invalidate() only affects objects safely accessible by the local CPU.  On multi-
     processor 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

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