POOL_INIT(9) | Kernel Developer's Manual | POOL_INIT(9) |
pool_init
,
pool_destroy
, pool_get
,
pool_put
, pool_prime
,
pool_setipl
, pool_sethiwat
,
pool_setlowat
,
pool_sethardlimit
—
resource-pool manager
#include
<sys/types.h>
#include <sys/pool.h>
void
pool_init
(struct pool *pool,
size_t size, u_int align,
u_int align_offset, int flags,
const char *wmesg, struct
pool_allocator *palloc);
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_setipl
(struct
pool *pp, int
ipl);
void
pool_sethiwat
(struct
pool *pp, int
n);
void
pool_setlowat
(struct
pool *pp, int
n);
int
pool_sethardlimit
(struct pool
*pp, unsigned n, const char
*warnmess, int ratecap);
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
(malloc(9)). The pool manager
obtains memory by using the special-purpose memory allocator
palloc passed to
pool_init
(),
for extra pool items in case the number of allocations exceeds the nominal
number of pool items managed by a pool resource. This temporary memory will
be automatically returned to the system at a later time.
The function pool_init
() initializes a
resource pool. The arguments are:
pool_get
().
This argument must be a power of two. If zero, the alignment defaults to
an architecture-specific natural alignment.pool_get
() must wait for items to be returned to
the pool.NULL
, in which
case the pool manager chooses an appropriate back-end allocator. If the
PR_WAITOK
flag has been specified, this allocator
may not be interrupt safe. It is recommended to specify this flag if the
pool will never be accessed in interrupt context.The
pool_destroy
()
function destroys a resource pool. It takes a single argument
pp identifying the pool resource instance.
pool_get
() allocates an item from the pool
and returns a pointer to it.
PR_WAITOK
or
PR_NOWAIT
must be specified to define behaviour in
case the pooled resources are depleted. If no resources are available and
PR_NOWAIT
was specified, this function returns
NULL
. If PR_WAITOK
was
specified but PR_LIMITFAIL
was not,
pool_get
() will wait until items are returned to
the pool. If both PR_WAITOK
and
PR_LIMITFAIL
were 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. If PR_ZERO
was specified
and an item has been successfully allocated, it is zeroed before being
returned to the caller.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 returned to the system if
possible.
pool_get
().If a non-interrupt safe allocator has been selected
by passing the PR_WAITOK
flag to
pmap_init
(),
pool_put
()
may sleep when completely unused pages are released.
pool_prime
() adds items to the pool.
Storage space for the items is allocated by using the page allocation
routine specified to pool_init
().
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 functions pool_sethiwat
() and
pool_setlowat
() set a pool's high and low
watermarks, respectively.
pool_prime
(), this function does not allocate the
necessary memory up-front.The pool_setipl
() function is used to
specify the interrupt protection level at which the pool can be safely
used.
The function
pool_sethardlimit
()
sets a hard limit on the pool to n items. If the hard
limit is reached warnmess will be printed to the
console, but no more than every ratecap seconds. Upon
successful completion, a value of 0 is returned. The value EINVAL is
returned when the current size of the pool already exceeds the requested
hard limit.
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 reentered.
To debug a misbehaving pool, a kernel can be compiled with the
MALLOC_DEBUG
option and memory debugging on pools
can be enabled with the PR_DEBUG
flag passed in the
flags argument in the call to
pool_init
().
See malloc(9) for more
information about MALLOC_DEBUG
. Alternatively, the
PR_DEBUGCHK
flag can be passed to enable pool
internal consistency checks before and after each allocation and free.
pool_init
(),
pool_destroy
(),
pool_prime
(), pool_setipl
(),
pool_sethiwat
(),
pool_setlowat
(), and
pool_sethardlimit
() can be called during autoconf or
from process context.
pool_get
() and
pool_put
() can be called during autoconf or from
process context. If the pool has been initialised with an interrupt safe
pool allocator they can also be called from interrupt context at or below
the interrupt level specified by a call to
pool_setipl
().
pool_get
() will return a pointer to an
item allocated from the pool. If PR_NOWAIT
or
PR_LIMITFAIL
were passed as flags to the pool it may
return NULL
if there are no resources available or
if the pool hard limit has been reached, respectively.
pool_prime
() will return
ENOMEM
if the requested number of items could not be
allocated. Otherwise, the return value is 0.
pool_sethardlimit
() will return
EINVAL
if the current size of the pool exceeds the
requested hard limit. Otherwise, the return value is 0.
The pool manager is implemented in the file sys/kern/subr_pool.c.
The pool manager first appeared in NetBSD 1.4 and was ported to OpenBSD by Artur Grabowski <art@openbsd.org>.
November 23, 2015 | OpenBSD-5.9 |