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.\"
.\" Copyright (C) 2001 Chad David <davidc@acns.ab.ca>. All rights reserved.
.\"
.\" 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(s), this list of conditions and the following disclaimer as
.\" the first lines of this file unmodified other than the possible
.\" addition of one or more copyright notices.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice(s), this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``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 COPYRIGHT HOLDER(S) 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 CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
.\" DAMAGE.
.\"
.\" $FreeBSD$
.\"
.Dd July 13, 2001
.Dt VM_PAGE_HOLD 9
.Os
.Sh NAME
.Nm vm_page_hold ,
.Nm vm_page_unhold
.Nd "update a page's hold count"
.Sh SYNOPSIS
.In sys/param.h
.In vm/vm.h
.In vm/vm_page.h
.Ft void
.Fn vm_page_hold "vm_page_t m"
.Ft void
.Fn vm_page_unhold "vm_page_t m"
.Sh DESCRIPTION
The
.Fn vm_page_hold
function increases the hold count on a page.
This prevents the page daemon from freeing the page.
.Pp
.Fn vm_page_hold
should only be used for very temporary wiring of a page,
as that page will not be considered for paging or
reallocation for as long as its hold count is greater
than zero.
Also note that while wired pages are removed from whatever
queue they are on,
.Fn vm_page_hold
does not affect the location of the page.
If it is on a queue prior to the call, it will still
be there afterward.
.Pp
If the page needs to be held for a long period of time,
.Xr vm_page_wire 9
should be used.
.Pp
.Fn vm_page_unhold
function reduces the hold count on a page.
If the hold count is zero it is possible that the page will be freed by the
page daemon.
.Sh SEE ALSO
.Xr vm_page_unwire 9 ,
.Xr vm_page_wire 9
.Sh AUTHORS
This manual page was written by
.An Chad David Aq davidc@acns.ab.ca .
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