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.\"     $NetBSD: pool_cache.9,v 1.13 2009/10/15 20:50:13 thorpej Exp $
.\"
.\" Copyright (c)2003 YAMAMOTO Takashi,
.\" All rights reserved.
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.\" modification, are permitted provided that the following conditions
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.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Paul Kranenburg; by Jason R. Thorpe of the Numerical Aerospace
.\" Simulation Facility, NASA Ames Research Center, and by Andrew Doran.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
.\" PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" ------------------------------------------------------------
.Dd October 15, 2009
.Dt POOL_CACHE 9
.Os
.\" ------------------------------------------------------------
.Sh NAME
.Nm pool_cache ,
.Nm pool_cache_init ,
.Nm pool_cache_destroy ,
.Nm pool_cache_get_paddr ,
.Nm pool_cache_get ,
.Nm pool_cache_put_paddr ,
.Nm pool_cache_put ,
.Nm pool_cache_destruct_object ,
.Nm pool_cache_invalidate ,
.Nm pool_cache_sethiwat ,
.Nm pool_cache_setlowat
.Nd resource-pool cache manager
.\" ------------------------------------------------------------
.Sh SYNOPSIS
.In sys/pool.h
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Ft pool_cache_t
.Fn 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"
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Ft void
.Fn pool_cache_destroy \
"pool_cache_t pc"
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Ft void *
.Fn pool_cache_get_paddr \
"pool_cache_t pc" "int flags" "paddr_t *pap"
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Ft void *
.Fn pool_cache_get \
"pool_cache_t pc" "int flags"
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Ft void
.Fn pool_cache_put_paddr \
"pool_cache_t pc" "void *object" "paddr_t pa"
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Ft void
.Fn pool_cache_put \
"pool_cache_t pc" "void *object"
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Ft void
.Fn pool_cache_destruct_object \
"pool_cache_t pc" "void *object"
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Ft void
.Fn pool_cache_invalidate \
"pool_cache_t pc"
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Ft void
.Fn pool_cache_sethiwat \
"pool_cache_t pc" "int nitems"
.Ft void
.Fn pool_cache_setlowat \
"pool_cache_t pc" "int nitems"
.\" ------------------------------------------------------------
.Sh 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.
.Pp
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 multiprocessor systems.
.\" ------------------------------------------------------------
.Sh FUNCTIONS
.Bl -tag -width compact
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.It Fn pool_cache_init "size" "align" "align_offset" "flags" \
"name" "palloc" "ipl"  "ctor" "dtor" "arg"
.Pp
Allocate and initialize a pool cache.
The arguments are:
.Pp
.Bl -tag -width four
.It Fa size
.Pp
Specifies the size of the memory items managed by the pool.
.It Fa align
.Pp
Specifies the memory address alignment of the items returned by
.Fn pool_cache_get .
This argument must be a power of two.
If zero,
the alignment defaults to an architecture-specific natural alignment.
.It Fa align_offset
.Pp
The offset within an item to which the
.Fa align
parameter applies.
.It Fa flags
.Pp
Should be set to zero or
.Dv PR_NOTOUCH .
If
.Dv 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.
.It Fa name
.Pp
The name used to identify the object in diagnostic output.
.It Fa palloc
.Pp
Should be typically be set to NULL, instructing
.Fn 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.
.It Fa ipl
.Pp
Specifies an interrupt priority level that will block all interrupt
handlers that could potentially access the pool.
The
.Nm
facility provides its own synchronization.
The users of any given
.Nm
need not provide additional synchronization for access to it.
.It Fa ctor
.Pp
Specifies a constructor used to initialize newly allocated objects.
If no constructor is required, specify
.Dv NULL .
.It Fa dtor
.Pp
Specifies a destructor used to destroy cached objects prior to
their release to backing store.
If no destructor is required, specify
.Dv NULL .
.It Fa arg
.Pp
This value of this argument will be passed to both the constructor
and destructor routines.
.El
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.It Fn pool_cache_destroy "pc"
.Pp
Destroy a pool cache
.Fa pc .
All other access to the cache must be stopped before this call
can be made.
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.It Fn pool_cache_get_paddr "pc" "flags" "pap"
.Pp
Get an object from a pool cache
.Fa pc .
If
.Fa pap
is not
.Dv NULL ,
physical address of the object or
.Dv POOL_PADDR_INVALID
will be returned via it.
.Fa flags
will be passed to
.Fn pool_get
function of the backing
.Xr pool 9
and the object constructor specified when the pool cache is created by
.Fn pool_cache_init .
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.It Fn pool_cache_get "pc" "flags"
.Pp
.Fn pool_cache_get
is the same as
.Fn pool_cache_get_paddr
with
.Dv NULL
.Fa pap
argument.
It's implemented as a macro.
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.It Fn pool_cache_put_paddr "pc" "object" "pa"
.Pp
Put an object
.Fa object
back to the pool cache
.Fa pc .
.Fa pa
should be physical address of the object
.Fa object
or
.Dv POOL_PADDR_INVALID .
.Fa pp .
If the number of available items in the backing pool exceeds the maximum
pool size set by
.Fn pool_cache_sethiwat
and there are no outstanding requests for pool items,
the excess items will be returned to the system.
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.It Fn pool_cache_put "pc" "object"
.Pp
.Fn pool_cache_put
is the same as
.Fn pool_cache_put_paddr
with
.Dv POOL_PADDR_INVALID
.Fa pa
argument.
It's implemented as a macro.
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.It Fn pool_cache_destruct_object "pc" "object"
.Pp
Force destruction of an object
.Fa object
and its release back into the pool.
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.It Fn pool_cache_invalidate "pc"
.Pp
Invalidate a pool cache
.Fa 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.
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.It Fn pool_cache_sethiwat "pc" "nitems"
.Pp
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
.Sy watermarks .
.Pp
The function
.Fn 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.
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.It Fn pool_cache_setlowat "pc" "nitems"
.Pp
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.
.El
.\" ------------------------------------------------------------
.Sh CODE REFERENCES
This section describes places within the
.Nx
source tree where actual code implementing the
.Nm
subsystem
can be found.
All pathnames are relative to
.Pa /usr/src .
.Pp
The
.Nm
subsystem is implemented within the file
.Pa sys/kern/subr_pool.c .
.Sh SEE ALSO
.Xr intro 9 ,
.Xr kmem 9 ,
.Xr memoryallocators 9 ,
.Xr pool 9