INITIALIZING A POOL

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 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.

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 resource pool. The POOL_INIT() macro has the same arguments as the pool_init() function and the resource pool will be initialized automatically during system startup.

DESTROYING A POOL

ALLOCATING ITEMS FROM A POOL

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 specified, 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

pp

The handle identifying the pool resource instance.

item

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

PRIMING A POOL

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

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 functions pool_sethiwat() and pool_setlowat() set a pool's high and low watermarks, 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 reclaim 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 allocate 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 warning message is issued when the pool hits its hard limit again.

POTENTIAL PITFALLS

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 reentered. Additionally, the functions pool_init() and pool_destroy() should never be called in interrupt context.

DIAGNOSTICS