Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages

  
 
  

home | help
POOL(9)			 BSD Kernel Developer's	Manual		       POOL(9)

NAME
     pool_init,	pool_destroy, pool_get,	pool_put, pool_prime, pool_sethiwat,
     pool_setlowat, pool_sethardlimit -- resource-pool manager

SYNOPSIS
     #include <sys/pool.h>

     void
     pool_init(struct pool *pp,	size_t size, u_int align, u_int	align_offset,
	 int flags, const char *wchan, struct pool_allocator *palloc,
	 int ipl);

     void
     pool_destroy(struct pool *pp);

     void *
     pool_get(struct pool *pp, int flags);

     void
     pool_put(struct pool *pp, void *item);

     int
     pool_prime(struct pool *pp, int nitems);

     void
     pool_sethiwat(struct pool *pp, int	n);

     void
     pool_setlowat(struct pool *pp, int	n);

     void
     pool_sethardlimit(struct pool *pp,	int n, 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 (malloc(9)).

   INITIALIZING	A POOL
     The function pool_init() initializes a resource pool.  The	arguments are:

	   pp		 The handle identifying	the pool resource instance.

	   size		 Specifies the size of the memory items	managed	by the
			 pool.

	   align	 Specifies the memory address alignment	of the items
			 returned by pool_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 parame-
			 ter 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.

	   wchan	 The `wait channel' passed on to cv_wait(9) if
			 pool_get() must wait for items	to be returned to the
			 pool.

	   palloc	 Can be	set to NULL or pool_allocator_kmem, in which
			 case the default kernel memory	allocator will be
			 used.	It can also be set to pool_allocator_nointr
			 when the pool will never be accessed from interrupt
			 context.

	   ipl		 Specifies an interrupt	priority level that will block
			 all interrupt handlers	that could potentially access
			 the pool.

     The POOL_INIT() macro can be used to both declare and initialize a	re-
     source pool.  The POOL_INIT() macro has the same arguments	as the
     pool_init() function and the resource pool	will be	initialized automati-
     cally during system startup.

   DESTROYING A	POOL
     The function pool_destroy() destroys a resource pool.  It takes a single
     argument pp identifying the pool resource instance.

   ALLOCATING ITEMS FROM A POOL
     pool_get()	allocates an item from the pool	and returns a pointer to it.
     The arguments are:

	   pp	  The handle identifying the pool resource instance.

	   flags  The flags can	be used	to define behaviour in case the	pooled
		  resources are	depleted.  If no resources are available and
		  PR_NOWAIT is given, pool_get() returns NULL.	If PR_WAITOK
		  is given and allocation is attempted with no resources
		  available, the function will sleep until items are returned
		  to the pool.	If both	PR_LIMITFAIL and PR_WAITOK are speci-
		  fied,	and the	pool has reached its hard limit, pool_get()
		  will return NULL without waiting, allowing the caller	to do
		  its own garbage collection; however, it will still wait if
		  the pool is not yet at its hard limit.

   RETURNING ITEMS TO A	POOL
     pool_put()	returns	the pool item pointed at by item to the	resource pool
     identified	by the pool handle pp.	If the number of available items in
     the pool exceeds the maximum pool size set	by pool_sethiwat() and there
     are no outstanding	requests for pool items, the excess items will be re-
     turned to the system.  The	arguments to pool_put()	are:

	   pp	 The handle identifying	the pool resource instance.

	   item	 A pointer to a	pool item previously obtained by pool_get().

   PRIMING A POOL
     pool_prime() adds items to	the pool.  Storage space for the items is al-
     located by	using the page allocation routine specified to pool_create().

     The arguments to pool_prime() are:

	   pp	    The	handle identifying the pool resource instance.

	   nitems   The	number of items	to add to the pool.

     This function may return ENOMEM in	case the requested number of items
     could not be allocated.  Otherwise, the return value is 0.

   SETTING POOL	RESOURCE WATERMARKS AND	LIMITS
     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 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	func-
     tions pool_sethiwat() and pool_setlowat() set a pool's high and low wa-
     termarks, respectively.

     The hard limit represents the maximum number of items a pool is allowed
     to	allocate at any	given time.  Unless modified via pool_sethardlimit(),
     the hard limit defaults to	UINT_MAX.

     pool_sethiwat()

	   pp	  The handle identifying the pool resource instance.

	   n	  The maximum number of	items to keep in the pool.  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 re-
		  claim	unused pages.

     pool_setlowat()

	   pp	  The handle identifying the pool resource instance.

	   n	  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.  Unlike pool_prime(), this function	does not allo-
		  cate the necessary memory up-front.

     pool_sethardlimit()

	   pp	  The handle identifying the pool resource instance.

	   n	  The maximum number of	items to be allocated from the pool
		  (i.e.	the hard limit).

	   warnmess
		  The warning message that will	be logged when the hard	limit
		  is reached.

	   ratecap
		  The minimal interval (in seconds) after which	another	warn-
		  ing message is issued	when the pool hits its hard limit
		  again.

   POTENTIAL PITFALLS
     Note that undefined behaviour results when	mixing the storage providing
     methods supported by the pool resource routines.

     The pool resource code uses a per-pool lock to protect its	internal
     state.  If	any pool functions are called in an interrupt context, the
     caller must block all interrupts that might cause the code	to be reen-
     tered.  Additionally, the functions pool_init() and pool_destroy()	should
     never be called in	interrupt context.

   DIAGNOSTICS
     Pool usage	logs can be enabled by defining	the compile-time option
     POOL_DIAGNOSTIC.

CODE REFERENCES
     The pool manager is implemented in	the file sys/kern/subr_pool.c.

SEE ALSO
     free(9), malloc(9), memoryallocators(9), pool_cache(9), uvm(9)

HISTORY
     The NetBSD	pool manager appeared in NetBSD	1.4.

BSD			       November	14, 2011			   BSD

NAME | SYNOPSIS | DESCRIPTION | CODE REFERENCES | SEE ALSO | HISTORY

Want to link to this manual page? Use this URL:
<https://www.freebsd.org/cgi/man.cgi?query=pool&sektion=9&manpath=NetBSD+6.0>

home | help