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.Dd August 31, 2011
.Dt VM_PAGE_AFLAG 9
.Os
.Sh NAME
.Nm vm_page_aflag_clear , vm_page_aflag_set , vm_page_reference
.Nd "change page atomic flags"
.Sh SYNOPSIS
.In sys/param.h
.In vm/vm.h
.In vm/vm_page.h
.Ft void
.Fn vm_page_aflag_clear "vm_page_t m" "uint8_t bits"
.Ft void
.Fn vm_page_aflag_set "vm_page_t m" "uint8_t bits"
.Ft void
.Fn vm_page_reference "vm_page_t m"
.Sh DESCRIPTION
The
.Fn vm_page_aflag_clear
atomically clears the specified bits on the page's
.Va aflags .
.Pp
The
.Fn vm_page_aflag_set
atomically sets the specified bits on the page's
.Va aflags .
.Pp
The
.Fn vm_page_reference m
call is the same as
.Bd -literal -offset indent
vm_page_aflag_set(m, PGA_REFERENCED);
.Ed
.Lp
and is the recommended way to mark the page as referenced from
third-party kernel modules.
.Pp
These functions neither block nor require any locks to be held
around the calls for correctness.
.Pp
The functions arguments are:
.Bl -tag -width ".Fa bits"
.It Fa m
The page whose
.Va aflags
are updated.
.It Fa bits
The bits that are set or cleared on the page's flags.
.El
.Pp
The following
.Va aflags
can be set or cleared:
.Bl -tag -width ".Fa PGA_REFERENCED"
.It Fa PGA_REFERENCED
The bit may be set to indicate that the page has been recently accessed.
For instance,
.Xr pmap 9
sets this bit to reflect the accessed attribute of the page mapping
typically updated by processor's memory management unit on the page access.
.It Fa PGA_WRITEABLE
A writeable mapping for the page may exist.
.El
.Pp
Both
.Dv PGA_REFERENCED
and
.Dv PGA_WRITEABLE
bits are only valid for the managed pages.
.Sh AUTHORS
This manual page was written by
.An Chad David Aq davidc@acns.ab.ca .