POOL_CACHE(9)          NetBSD 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 -- 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);

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.

     Global and per-CPU caches of constructed objects are maintained.  The two
     levels of cache work together to allow for low overhead allocation and
     release of objects, and improved L1/L2/L3 hardware cache locality in mul-
     tiprocessor systems.

FUNCTIONS
     pool_cache_init(pc, pp, 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 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.

              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 addi-
                    tional synchronization for access to it.

              ctor

                    Specifies a constructor used to initialize newly allocated
                    objects.  If no constructor is required, specify NULL.

              dtor

                    Specifies a destructor used to destroy cached objects
                    prior to their release to backing store.  If no destructor
                    is required, specify NULL.

              arg

                    This value of this argument will be passed to both the
                    constructor and destructor routines.

     pool_cache_destroy(pc)

              Destroy a pool cache.  All other access to the cache must be
              stopped before this call can be made.  pc.

     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(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 its release back into
              the pool.

     pool_cache_invalidate(pc)

              Invalidate a pool cache pc.  Destruct and release all objects in
              the global cache.  Per-CPU caches will not be invalidated by
              this call, meaning that it is still possible to allocate "stale"
              items from the cache.  If relevant, the user must check for this
              condition when allocating items.

     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 number 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 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
              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 func-
              tion.

CODE REFERENCES
     This section describes places within the NetBSD source tree where actual
     code implementing the pool_cache subsystem can be found.  All pathnames
     are relative to /usr/src.

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

SEE ALSO
     intro(9), kmem_alloc(9), kmem_free(9), memoryallocators(9), pool(9)

NetBSD 5.0.1                    Febuary 1, 2008                   NetBSD 5.0.1

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