Updated: 2021/Apr/14


POOL_CACHE(9)              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 n);

     void
     pool_cache_setlowat(pool_cache_t pc, int n);

     void
     pool_cache_sethardlimit(pool_cache_t pc, 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
     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 synchronization 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.  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.

     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, n)

              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
              free items in the pool exceed a programmable limit.  The limits
              for the minimum and maximum number of free items which a pool
              should try to keep available are known as the high and low
              watermarks.

              The function pool_cache_sethiwat() sets the backing pool's high
              water mark.  As items are freed and the number of free items 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, n)

              Set the minimum number of free items to try to keep in the pool.
              When the number of free items in the pool drops below this
              threshold, a non-blocking attempt is made to allocate memory for
              more items.  The number of free items is not guaranteed to
              remain above this threshold.

     pool_cache_sethardlimit(pc, n, warnmess, ratecap)
              Set the maximum number of total items (both free and allocated)
              for the backing pool(9) to n.  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.

     pool_cache_prime(pc, n)
              Set the minimum number of total items (both free and allocated)
              for the backing pool(9) to n.

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)

NetBSD 9.99                     April 12, 2020                     NetBSD 9.99