7b2064c2a5
missing description of pool_destroy(). Fix some minor nits. It isn't clear from the source whether pool_reclaim() and pool_drain() should belong to the exported API. At least it seems they aren't used. No descriptions for these functions exist in this manpage.
343 lines
10 KiB
Groff
343 lines
10 KiB
Groff
.\" $NetBSD: pool.9,v 1.19 2001/07/19 21:35:53 gmcgarry Exp $
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.\"
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.\" Copyright (c) 1997, 1998 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by Paul Kranenburg.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the NetBSD
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.\" Foundation, Inc. and its contributors.
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.\" 4. Neither the name of The NetBSD Foundation nor the names of its
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.\" contributors may be used to endorse or promote products derived
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.\" from this software without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd July 20, 2001
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.Dt POOL 9
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.Os
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.Sh NAME
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.Nm pool_init ,
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.Nm pool_destroy ,
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.Nm pool_get ,
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.Nm pool_put ,
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.Nm pool_prime ,
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.Nm pool_sethiwat ,
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.Nm pool_setlowat
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.\".Nm POOL_STORAGE_SIZE
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.Nd resource-pool manager
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.Sh SYNOPSIS
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.Fd #include <sys/pool.h>
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.Ft void
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.Fo pool_init
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.Fa "struct pool *"
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.Fa "size_t size"
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.Fa "u_int align"
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.Fa "u_int align_offset"
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.Fa "int nitems"
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.Fa "char *wchan"
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.Fa "u_int pagesz"
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.Fa "void *(*palloc)(unsigned long sz, int flags, int tag)"
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.Fa "void (*prelease)(void *v, unsigned long sz, int tag)"
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.Fa "int mtag"
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.Fc
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.Ft void
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.Fn pool_destroy "struct pool *pp"
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.Ft void *
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.Fn pool_get "struct pool *pp" "int flags"
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.Ft void
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.Fn pool_put "struct pool *pp" "void *item"
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.Ft int
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.Fn pool_prime "struct pool *pp" "int nitems" "caddr_t storage"
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.Ft void
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.Fn pool_sethiwat "struct pool *pp" "int n"
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.Ft void
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.Fn pool_setlowat "struct pool *pp" "int n"
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.Fn POOL_STORAGE_SIZE "size" "nitems"
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.Sh DESCRIPTION
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These utility routines provide management of pools of fixed-sized
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areas of memory.
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Resource pools set aside an amount of memory for exclusive use by the resource
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pool owner.
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This can be used by applications to guarantee the availability of a minimum
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amount of memory needed to continue operation independent of the memory
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resources currently available from the system-wide memory allocator
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.Pq Xr malloc 9 .
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The pool manager can optionally obtain temporary memory by calling the
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.Fn palloc
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function passed to
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.Fn pool_init ,
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for extra pool items in case the number of allocations exceeds
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the nominal number of pool items managed by a pool resource.
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This temporary memory will be automatically returned to the system
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at a later time.
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.Ss INITIALIZING A POOL
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The function
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.Fn pool_init
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initializes a resource pool.
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The arguments are:
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.Pp
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.Bl -tag -offset indent -width "prelease"
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.It Fa pp
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The handle identifying the pool resource instance.
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.It Fa size
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Specifies the size of the memory items managed by the pool.
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.It Fa align
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Specifies the memory address alignment of the items returned by
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.Fn pool_get .
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This argument must be a power of two.
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If zero,
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the alignment defaults to a architecture-specific natural alignment.
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.It Fa align_offset
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The offset within an item to which the
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.Fa align
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parameter applies.
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.It Fa nitems
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Specifies the number of memory items that are allocated to
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the pool at creation time.
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This number may be zero,
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in which case
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.Fn pool_prime
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can be used at a later time to add permanent items to the pool.
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.It Fa wchan
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The
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.Sq wait channel
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passed on to
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.Xr tsleep 9
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if
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.Fn pool_get
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must wait for items to be returned to the pool.
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.It Fa pagesz
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The unit which is used to allocate additional memory to the pool.
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It must be a power of two.
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.It Fa palloc
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is called to add additional memory if the pool is depleted.
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It must return
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.Fa pagesz
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aligned memory.
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The argument
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.Fa sz
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shall be a multiple of
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.Fa pagesz .
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.It Fa prelease
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is called to release pages back to the system.
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.Fn palloc
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and
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.Fn prelease
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may be
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.Dv NULL ,
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in which case the pool manager uses
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.Xr uvm_km_kmemalloc 9
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and
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.Xr uvm_km_free 9
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to allocate and release memory using the
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.Em kernel_map
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.Po
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see
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.Xr uvm 9
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.Pc .
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.It Fa mtag
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The memory tag passed to
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.Fn palloc
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and
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.Fn prelease
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when allocating or releasing memory pages.
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.El
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.Pp
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.\"The macro
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.\".Fn POOL_STORAGE_SIZE "size" "nitems"
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.\"can be used to determine the amount of storage needed to setup a pool,
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.\"given the size and number of the pool items.
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.Ss DESTROYING A POOL
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The function
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.Fn pool_destroy
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destroys a resource pool. It takes a single argument
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.Fa pp
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identifying the pool resource instance.
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.Ss ALLOCATING ITEMS FROM A POOL
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.Fn pool_get
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allocates an item from the pool and returns a pointer to it.
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The arguments are:
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.Bl -tag -offset indent -width "flags"
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.It Fa pp
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The handle identifying the pool resource instance.
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.It Fa flags
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One or more of of
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.Dv PR_URGENT ,
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.Dv PR_WAITOK
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or
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.Dv PR_LIMITFAIL ,
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that define behaviour in case the pooled resources are depleted.
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If no resources are available and
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.Dv PR_WAITOK
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is given,
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this function will wait until items are returned to the pool.
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Otherwise
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.Fn pool_get
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returns
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.Dv NULL .
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If
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.Dv PR_URGENT
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is specified and no items are available and
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.Fn palloc
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cannot allocate a new page,
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the system will panic
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.Pq XXX .
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.\"Undefined behaviour results if
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.\".Dv PR_MALLOCOK
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.\"is specified on a pool handle that was created using client-provided
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.\"storage.
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.\" a bunch of other flags aren't documented.
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If both
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.Dv PR_LIMITFAIL
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and
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.Dv PR_WAITOK
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is specified, and the pool has reached its hard limit,
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.Fn pool_get
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will return
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.Dv NULL
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without waiting, allowing the caller to do its own garbage collection;
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however, it will still wait if the pool is not yet at its hard limit.
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.El
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.Ss RETURNING ITEMS TO A POOL
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.Fn pool_put
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returns the pool item pointed at by
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.Fa item
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to the resource pool identified by the pool handle
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.Fa pp .
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If the number of available items in the pool exceeds the maximum pool
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size set by
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.Fn pool_sethiwat
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and there are no outstanding requests for pool items,
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the excess items will be returned to the system by calling
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.Fn prelease .
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The arguments to
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.Fn pool_put
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are:
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.Bl -tag -offset indent -width "item"
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.It Fa pp
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The handle identifying the pool resource instance.
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.It Fa item
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A pointer to a pool item previously obtained by
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.Fn pool_get .
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.El
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.Ss PRIMING A POOL
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.Fn pool_prime
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adds items to the pool.
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Storage space for the items is either allocated by using the page allocation
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routine specified to
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.Fn pool_create ,
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or provided to
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.Fn pool_prime
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by the caller through the
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.Fa storage
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parameter.
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.Pp
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The arguments to
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.Fn pool_prime
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are:
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.Bl -tag -offset indent -width "nitems"
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.It Fa pp
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The handle identifying the pool resource instance.
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.It Fa nitems
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The number of items to add to the pool.
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.It Fa storage
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Optional pre-allocated storage.
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.El
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.Pp
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This function may return
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.Dv ENOMEM
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in case the requested number of items could not be allocated.
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Otherwise,
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the return value is 0.
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.Ss SETTING POOL RESOURCE WATERMARKS
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A pool will attempt to increase its resource usage to keep up with the demand
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for its items.
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Conversely,
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it will return unused memory to the system should the number of accumulated
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unused items in the pool exceed a programmable limit.
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The limits for the minimum and maximum number of items which a pool should keep
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at hand are known as the high and low
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.Sy watermarks .
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The functions
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.Fn pool_sethiwat
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and
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.Fn pool_setlowat
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set a pool's high and low watermarks, respectively.
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.Pp
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.Fn pool_sethiwat
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.Bl -tag -offset indent -width "flags"
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.It Fa pp
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The handle identifying the pool resource instance.
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.It Fa n
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The maximum number of items to keep in the pool.
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As items are returned and the total number of pages in the pool is larger
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than the maximum set by this function,
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any completely unused pages are released immediately
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.Pq by calling Fn prelease .
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If this function is not used to specify a maximum number of items,
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the pages will remain associated with the pool until the system runs low
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on memory,
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at which point the VM system will try to reclaim unused pages.
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.El
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.Pp
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.Fn pool_setlowat
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.Bl -tag -offset indent -width "flags"
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.It Fa pp
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The handle identifying the pool resource instance.
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.It Fa n
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The minimum number of items to keep in the pool.
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The number pages in the pool will not decrease below the required value to
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accommodate the minimum number of items specified by this function.
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Unlike
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.Fn pool_prime ,
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this function does not allocate the necessary memory up-front.
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.El
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.Ss POTENTIAL PITFALLS
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Note that undefined behaviour results when mixing the storage providing
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methods supported by the pool resource routines.
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.Pp
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The pool resource code uses a per-pool lock to protect its internal state.
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If any pool functions are called in an interrupt context,
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the caller must block all interrupts that might cause the
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code to be reentered.
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.Ss DIAGNOSTICS
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Pool usage logs can be enabled by defining the compile-time option
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.Dv POOL_DIAGNOSTIC .
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.\" .Sh RETURN VALUES
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.\" .Sh EXAMPLES
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.Sh CODE REFERENCES
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The pool manager is implemented in the file
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.Pa sys/kern/subr_pool.c .
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.\" .Sh AUTHOR
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.Sh SEE ALSO
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.Xr malloc 9 ,
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.Xr free 9 ,
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.Xr uvm 9
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.Sh HISTORY
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The
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.Nx
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pool manager appeared in
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.Nx 1.4 .
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