The soft and hard busy mechanism rely on the vm object lock to work.

Unify the 2 concept into a real, minimal, sxlock where the shared
acquisition represent the soft busy and the exclusive acquisition
represent the hard busy.
The old VPO_WANTED mechanism becames the hard-path for this new lock
and it becomes per-page rather than per-object.
The vm_object lock becames an interlock for this functionality:
it can be held in both read or write mode.
However, if the vm_object lock is held in read mode while acquiring
or releasing the busy state, the thread owner cannot make any
assumption on the busy state unless it is also busying it.

Also:
- Add a new flag to directly shared busy pages while vm_page_alloc
  and vm_page_grab are being executed.  This will be very helpful
  once these functions happen under a read object lock.
- Move the swapping sleep into its own per-object flag

The KPI is heavilly changed this is why the version is bumped.
It is very likely that some VM ports users will need to change
their own code.

Sponsored by:	EMC / Isilon storage division
Discussed with:	alc
Reviewed by:	jeff, kib
Tested by:	gavin, bapt (older version)
Tested by:	pho, scottl

7 files changed, 238 insertions, 222 deletions

diff --git a/share/man/man9/Makefile b/share/man/man9/Makefile
index 86e89a7..3750c39 100644
--- a/share/man/man9/Makefile
+++ b/share/man/man9/Makefile
@@ -332,11 +332,8 @@ MAN=	accept_filter.9 \
 	vm_page_grab.9 \
 	vm_page_hold.9 \
 	vm_page_insert.9 \
-	vm_page_io.9 \
 	vm_page_lookup.9 \
 	vm_page_rename.9 \
-	vm_page_sleep_if_busy.9 \
-	vm_page_wakeup.9 \
 	vm_page_wire.9 \
 	vm_set_page_size.9 \
 	vmem.9 \
@@ -1465,6 +1462,21 @@ MLINKS+=vm_page_bits.9 vm_page_clear_dirty.9 \
 	vm_page_bits.9 vm_page_test_dirty.9 \
 	vm_page_bits.9 vm_page_undirty.9 \
 	vm_page_bits.9 vm_page_zero_invalid.9
+MLINKS+=vm_page_busy.9 vm_page_busied.9 \
+	vm_page_busy.9 vm_page_busy_downgrade.9 \
+	vm_page_busy.9 vm_page_busy_sleep.9 \
+	vm_page_busy.9 vm_page_sbusied.9 \
+	vm_page_busy.9 vm_page_sbusy.9 \
+	vm_page_busy.9 vm_page_sleep_if_busy.9 \
+	vm_page_busy.9 vm_page_sunbusy.9 \
+	vm_page_busy.9 vm_page_trysbusy.9 \
+	vm_page_busy.9 vm_page_tryxbusy.9 \
+	vm_page_busy.9 vm_page_xbusied.9 \
+	vm_page_busy.9 vm_page_xbusy.9 \
+	vm_page_busy.9 vm_page_xunbusy.9 \
+	vm_page_busy.9 vm_page_assert_sbusied.9 \
+	vm_page_busy.9 vm_page_assert_unbusied.9 \
+	vm_page_busy.9 vm_page_assert_xbusied.9
 MLINKS+=vm_page_aflag.9 vm_page_aflag_clear.9 \
 	vm_page_aflag.9 vm_page_aflag_set.9 \
 	vm_page_aflag.9 vm_page_reference.9
@@ -1473,10 +1485,6 @@ MLINKS+=vm_page_free.9 vm_page_free_toq.9 \
 	vm_page_free.9 vm_page_try_to_free.9
 MLINKS+=vm_page_hold.9 vm_page_unhold.9
 MLINKS+=vm_page_insert.9 vm_page_remove.9
-MLINKS+=vm_page_io.9 vm_page_io_finish.9 \
-	vm_page_io.9 vm_page_io_start.9
-MLINKS+=vm_page_wakeup.9 vm_page_busy.9 \
-	vm_page_wakeup.9 vm_page_flash.9
 MLINKS+=vm_page_wire.9 vm_page_unwire.9
 MLINKS+=VOP_ACCESS.9 VOP_ACCESSX.9
 MLINKS+=VOP_ATTRIB.9 VOP_GETATTR.9 \
diff --git a/share/man/man9/VOP_GETPAGES.9 b/share/man/man9/VOP_GETPAGES.9
index b165162..7869d45 100644
--- a/share/man/man9/VOP_GETPAGES.9
+++ b/share/man/man9/VOP_GETPAGES.9
@@ -102,7 +102,7 @@ When the write completes, the completion callback should
 call
 .Xr vm_object_pip_wakeup 9
 and
-.Xr vm_page_io_finish 9
+.Xr vm_page_sunbusy 9
 to clear the busy flag and awaken any other threads waiting for this page,
 in addition to calling
 .Xr vm_page_undirty 9 .
@@ -139,7 +139,7 @@ For example,
 .Fn VOP_GETPAGES
 may either activate a page (if its wanted bit is set)
 or deactivate it (otherwise), and finally call
-.Xr vm_page_wakeup 9
+.Xr vm_page_xunbusy 9
 to arouse any threads currently waiting for the page to be faulted in.
 .Sh RETURN VALUES
 If it successfully reads
@@ -156,9 +156,9 @@ is
 .Sh SEE ALSO
 .Xr vm_object_pip_wakeup 9 ,
 .Xr vm_page_free 9 ,
-.Xr vm_page_io_finish 9 ,
+.Xr vm_pagge_sunbusy 9 ,
 .Xr vm_page_undirty 9 ,
-.Xr vm_page_wakeup 9 ,
+.Xr vm_page_xunbusy 9 ,
 .Xr vnode 9
 .Sh AUTHORS
 This manual page was written by
diff --git a/share/man/man9/vm_page_alloc.9 b/share/man/man9/vm_page_alloc.9
index 9397d21..3109a3f 100644
--- a/share/man/man9/vm_page_alloc.9
+++ b/share/man/man9/vm_page_alloc.9
@@ -91,9 +91,7 @@ than zero.
 The optional flags are:
 .Bl -tag -width ".Dv VM_ALLOC_IFNOTCACHED"
 .It Dv VM_ALLOC_NOBUSY
-The returned page will not have the
-.Dv VPO_BUSY
-flag set.
+The returned page will not be exclusive busy.
 .It Dv VM_ALLOC_NODUMP
 The returned page will not be included in any kernel core dumps
 regardless of whether or not it is mapped in to KVA.
@@ -112,6 +110,8 @@ Only allocate the page if it is not cached in the
 If the page at the specified
 .Fa pindex
 is cached, NULL is returned instead.
+.It Dv VM_ALLOC_SBUSY
+The returned page will be shared busy.
 .It Dv VM_ALLOC_WIRED
 The returned page will be wired.
 .It Dv VM_ALLOC_ZERO
diff --git a/share/man/man9/vm_page_busy.9 b/share/man/man9/vm_page_busy.9
new file mode 100644
index 0000000..37a4efa
--- /dev/null
+++ b/share/man/man9/vm_page_busy.9
@@ -0,0 +1,216 @@
+.\"
+.\" Copyright (c) 2013 EMC Corp.
+.\" 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, 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.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``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 AUTHOR 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 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 August 07, 2013
+.Dt vm_page_busy 9
+.Os
+.Sh NAME
+.Nm vm_page_busied ,
+.Nm vm_page_busy_downgrade ,
+.Nm vm_page_busy_sleep ,
+.Nm vm_page_sbusied ,
+.Nm vm_page_sbusy ,
+.Nm vm_page_sleep_if_busy ,
+.Nm vm_page_sunbusy ,
+.Nm vm_page_trysbusy ,
+.Nm vm_page_tryxbusy ,
+.Nm vm_page_xbusied ,
+.Nm vm_page_xbusy ,
+.Nm vm_page_xunbusy ,
+.Nm vm_page_assert_sbusied ,
+.Nm vm_page_assert_unbusied ,
+.Nm vm_page_assert_xbusied
+.Nd protect page identity changes and page content references
+.Sh SYNOPSIS
+.In sys/param.h
+.In vm/vm.h
+.In vm/vm_page.h
+.Ft int
+.Fn vm_page_busied "vm_page_t m"
+.Ft void
+.Fn vm_page_busy_downgrade "vm_page_t m"
+.Ft void
+.Fn vm_page_busy_sleep "vm_page_t m" "const char *msg"
+.Ft int
+.Fn vm_page_sbusied "vm_page_t m"
+.Ft void
+.Fn vm_page_sbusy "vm_page_t m"
+.Ft int
+.Fn vm_page_sleep_if_busy "vm_page_t m" "const char *msg"
+.Ft void
+.Fn vm_page_sunbusy "vm_page_t m"
+.Ft int
+.Fn vm_page_trysbusy "vm_page_t m"
+.Ft int
+.Fn vm_page_tryxbusy "vm_page_t m"
+.Ft int
+.Fn vm_page_xbusied "vm_page_t m"
+.Ft void
+.Fn vm_page_xbusy "vm_page_t m"
+.Ft void
+.Fn vm_page_xunbusy "vm_page_t m"
+.Pp
+.Cd "options INVARIANTS"
+.Cd "options INVARIANT_SUPPORT"
+.Ft void
+.Fn vm_page_assert_sbusied "vm_page_t m"
+.Ft void
+.Fn vm_page_assert_unbusied "vm_page_t m"
+.Ft void
+.Fn vm_page_assert_xbusied "vm_page_t m"
+.Sh DESCRIPTION
+Page identity is usually protected by higher level locks like vm_object
+locks and vm page locks.
+However, sometimes it is not possible to hold such locks for the time
+necessary to complete the identity change.
+In such case the page can be exclusively busied by a thread which needs
+to own the identity for a certain amount of time.
+.Pp
+In other situations, threads do not need to change the identity of the
+page but they want to prevent other threads from changing the identity
+themselves.
+For example, when a thread wants to access or update page contents
+without a lock held the page is shared busied.
+.Pp
+Before busing a page the vm_object lock must be held.
+The same rule applies when a page is unbusied.
+This makes the vm_object lock a real busy interlock.
+.Pp
+The
+.Fn vm_page_busied
+function returns non-zero if the current thread busied
+.Fa m
+in either exclusive or shared mode.
+Returns zero otherwise.
+.Pp
+The
+.Fn vm_page_busy_downgrade
+function must be used to downgrade
+.Fa m
+from an exclusive busy state to a shared busy state.
+.Pp
+The
+.Fn vm_page_busy_sleep
+function puts the invoking thread to sleep using the appropriate
+waitchannels for the busy mechanism.
+The parameter
+.Fa msg
+is a string describing the sleep condition for userland tools.
+.Pp
+The
+.Fn vm_page_busied
+function returns non-zero if the current thread busied
+.Fa m
+in shared mode.
+Returns zero otherwise.
+.Pp
+The
+.Fn vm_page_sbusy
+function shared busies
+.Fa m .
+.Pp
+The
+.Fn vm_page_sleep_if_busy
+function puts the invoking thread to sleep, using the appropriate
+waitchannels for the busy mechanism, if
+.Fa m .
+is busied in either exclusive or shared mode.
+If the invoking thread slept a non-zero value is returned, otherwise
+0 is returned.
+The parameter
+.Fa msg
+is a string describing the sleep condition for userland tools.
+.Pp
+The
+.Fn vm_page_sunbusy
+function shared unbusies
+.Fa m .
+.Pp
+The
+.Fn vm_page_trysbusy
+attempts to shared busy
+.Fa m .
+If the operation cannot immediately succeed
+.Fn vm_page_trysbusy
+returns 0, otherwise a non-zero value is returned.
+.Pp
+The
+.Fn vm_page_tryxbusy
+attempts to exclusive busy
+.Fa m .
+If the operation cannot immediately succeed
+.Fn vm_page_tryxbusy
+returns 0, otherwise a non-zero value is returned.
+.Pp
+The
+.Fn vm_page_xbusied
+function returns non-zero if the current thread busied
+.Fa m
+in exclusive mode.
+Returns zero otherwise.
+.Pp
+The
+.Fn vm_page_xbusy
+function exclusive busies
+.Fa m .
+.Pp
+The
+.Fn vm_page_xunbusy
+function exclusive unbusies
+.Fa m .
+Assertions on the busy state allow kernels compiled with
+.Cd "options INVARIANTS"
+and
+.Cd "options INVARIANT_SUPPORT"
+to panic if they are not respected.
+.Pp
+The
+.Fn vm_page_assert_sbusied
+function panics if
+.Fa m
+is not shared busied.
+.Pp
+The
+.Fn vm_page_assert_unbusied
+function panics if
+.Fa m
+is not unbusied.
+.Pp
+The
+.Fn vm_page_assert_xbusied
+function panics if
+.Fa m
+is not exclusive busied.
+.Sh SEE ALSO
+.Xr VOP_GETPAGES 9 ,
+.Xr vm_page_aflag 9 ,
+.Xr vm_page_alloc 9 ,
+.Xr vm_page_deactivate 9 ,
+.Xr vm_page_free 9 ,
+.Xr vm_page_grab 9 ,
+.Xr vm_page_insert 9 ,
+.Xr vm_page_lookup 9 ,
+.Xr vm_page_rename 9
diff --git a/share/man/man9/vm_page_io.9 b/share/man/man9/vm_page_io.9
deleted file mode 100644
index bddb82b..0000000
--- a/share/man/man9/vm_page_io.9
+++ /dev/null
@@ -1,65 +0,0 @@
-.\"
-.\" 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 17, 2001
-.Dt VM_PAGE_IO_START 9
-.Os
-.Sh NAME
-.Nm vm_page_io_start ,
-.Nm vm_page_io_finish
-.Nd "ready or unready a page for I/O"
-.Sh SYNOPSIS
-.In sys/param.h
-.In vm/vm.h
-.In vm/vm_page.h
-.Ft void
-.Fn vm_page_io_start "vm_page_t m"
-.Ft void
-.Fn vm_page_io_finish "vm_page_t m"
-.Sh DESCRIPTION
-The
-.Fn vm_page_io_start
-function prepares the page for I/O by incrementing its busy flag by one.
-.Pp
-The
-.Fn vm_page_io_finish
-function lowers the busy count on the page by one, if the resulting busy
-count is zero, a
-.Xr wakeup 9
-will be issued if the page has been marked
-.Dv VPO_WANTED .
-A page is typically marked
-.Dv VPO_WANTED
-by a thread to register its interest in
-the page to either complete I/O or becoming available for general use.
-.Sh AUTHORS
-.An -nosplit
-This manual page was written by
-.An Chad David Aq davidc@acns.ab.ca
-and
-.An Alfred Perlstein Aq alfred@FreeBSD.org .
diff --git a/share/man/man9/vm_page_sleep_if_busy.9 b/share/man/man9/vm_page_sleep_if_busy.9
deleted file mode 100644
index 850979f..0000000
--- a/share/man/man9/vm_page_sleep_if_busy.9
+++ /dev/null
@@ -1,68 +0,0 @@
-.\"
-.\" 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_SLEEP_IF_BUSY 9
-.Os
-.Sh NAME
-.Nm vm_page_sleep_if_busy
-.Nd "wait for a busy page to become unbusy"
-.Sh SYNOPSIS
-.In sys/param.h
-.In vm/vm.h
-.In vm/vm_page.h
-.Ft int
-.Fn vm_page_sleep_if_busy "vm_page_t m" "int also_m_busy" "const char *wmesg"
-.Sh DESCRIPTION
-The
-.Fn vm_page_sleep_if_busy
-function waits until the
-.Dv VPO_BUSY
-flag is cleared.
-If
-.Fa also_m_busy
-is non-zero, it also waits for
-.Fa m->busy
-to become zero.
-.Sh RETURN VALUES
-If
-.Fn vm_page_sleep_if_busy
-finds the page busy it returns
-.Dv TRUE .
-If not, it returns
-.Dv FALSE .
-Returning
-.Dv TRUE
-does not necessary mean that
-.Fn vm_page_sleep_if_busy
-slept, but only that
-.Fn splvm
-was called.
-.Sh AUTHORS
-This manual page was written by
-.An Chad David Aq davidc@acns.ab.ca .
diff --git a/share/man/man9/vm_page_wakeup.9 b/share/man/man9/vm_page_wakeup.9
deleted file mode 100644
index 5908b62..0000000
--- a/share/man/man9/vm_page_wakeup.9
+++ /dev/null
@@ -1,75 +0,0 @@
-.\"
-.\" 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 14, 2001
-.Dt VM_PAGE_BUSY 9
-.Os
-.Sh NAME
-.Nm vm_page_busy ,
-.Nm vm_page_flash ,
-.Nm vm_page_wakeup
-.Nd "handle the busying and unbusying of a page"
-.Sh SYNOPSIS
-.In sys/param.h
-.In vm/vm.h
-.In vm/vm_page.h
-.Ft void
-.Fn vm_page_busy "vm_page_t m"
-.Ft void
-.Fn vm_page_flash "vm_page_t m"
-.Ft void
-.Fn vm_page_wakeup "vm_page_t m"
-.Sh DESCRIPTION
-These functions handle the busying, unbusying and notification of the unbusying
-of a page.
-.Pp
-.Fn vm_page_busy
-sets the
-.Dv VPO_BUSY
-flag in the page.
-.Pp
-.Fn vm_page_flash
-checks to see if there is anybody waiting on the page
-.Dv ( VPO_WANTED
-will be set), and if so, clears the
-.Dv VPO_WANTED
-flag and notifies whoever is waiting via
-.Fn wakeup .
-.Pp
-.Fn vm_page_wakeup
-clears the
-.Dv VPO_BUSY
-flag on the page, and calls
-.Fn vm_page_flash
-in case somebody has been waiting for it.
-.Sh SEE ALSO
-.Xr vm_page_sleep_if_busy 9 ,
-.Xr wakeup 9
-.Sh AUTHORS
-This manual page was written by
-.An Chad David Aq davidc@acns.ab.ca .