POOL_CACHE(9)

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 nitems);

void
`pool_cache_setlowat`(pool_cache_t pc, int nitems);

void
`pool_cache_sethardlimit`(pool_cache_t pc, int nitems, 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`. 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.

`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, 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 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 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 minimal interval (in seconds) after which another warning message is issued when the pool hits its hard limit again.

# 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)

November 15, 2011 | NetBSD 9.4