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.\" Copyright (C) 2001 Chad David <davidc@acns.ab.ca>. All rights reserved.
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.\" $FreeBSD: src/share/man/man9/vm_page_hold.9,v 1.4.36.1.6.1 2010/12/21 17:09:25 kensmith Exp $
.\"
.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 .