vm_page_busied
,
vm_page_busy_downgrade
,
vm_page_busy_sleep
,
vm_page_sbusied
,
vm_page_sbusy
,
vm_page_sleep_if_busy
,
vm_page_sunbusy
,
vm_page_trysbusy
,
vm_page_tryxbusy
,
vm_page_xbusied
,
vm_page_xbusy
,
vm_page_xunbusy
,
vm_page_assert_sbusied
,
vm_page_assert_unbusied
,
vm_page_assert_xbusied
—
protect page identity changes and page content
references
#include
<sys/param.h>
#include
<vm/vm.h>
#include
<vm/vm_page.h>
int
vm_page_busied
(
vm_page_t
m);
void
vm_page_busy_downgrade
(
vm_page_t
m);
void
vm_page_busy_sleep
(
vm_page_t
m,
const char
*msg);
int
vm_page_sbusied
(
vm_page_t
m);
void
vm_page_sbusy
(
vm_page_t
m);
int
vm_page_sleep_if_busy
(
vm_page_t
m,
const char
*msg);
void
vm_page_sunbusy
(
vm_page_t
m);
int
vm_page_trysbusy
(
vm_page_t
m);
int
vm_page_tryxbusy
(
vm_page_t
m);
int
vm_page_xbusied
(
vm_page_t
m);
void
vm_page_xbusy
(
vm_page_t
m);
void
vm_page_xunbusy
(
vm_page_t
m);
options INVARIANTS
options INVARIANT_SUPPORT
void
vm_page_assert_sbusied
(
vm_page_t
m);
void
vm_page_assert_unbusied
(
vm_page_t
m);
void
vm_page_assert_xbusied
(
vm_page_t
m);
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.
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.
Before busying 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.
The
vm_page_busied
() function returns
non-zero if the current thread busied
m in
either exclusive or shared mode. Returns zero otherwise.
The
vm_page_busy_downgrade
() function must be
used to downgrade
m from an exclusive busy
state to a shared busy state.
The
vm_page_busy_sleep
() function puts the
invoking thread to sleep using the appropriate waitchannels for the busy
mechanism. The parameter
msg is a string
describing the sleep condition for userland tools.
The
vm_page_busied
() function returns
non-zero if the current thread busied
m in
shared mode. Returns zero otherwise.
The
vm_page_sbusy
() function shared busies
m.
The
vm_page_sleep_if_busy
() function puts the
invoking thread to sleep, using the appropriate waitchannels for the busy
mechanism, if
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
msg is a string describing the sleep
condition for userland tools.
The
vm_page_sunbusy
() function shared
unbusies
m.
The
vm_page_trysbusy
() attempts to shared
busy
m. If the operation cannot immediately
succeed
vm_page_trysbusy
() returns 0,
otherwise a non-zero value is returned.
The
vm_page_tryxbusy
() attempts to exclusive
busy
m. If the operation cannot immediately
succeed
vm_page_tryxbusy
() returns 0,
otherwise a non-zero value is returned.
The
vm_page_xbusied
() function returns
non-zero if the current thread busied
m in
exclusive mode. Returns zero otherwise.
The
vm_page_xbusy
() function exclusive busies
m.
The
vm_page_xunbusy
() function exclusive
unbusies
m. Assertions on the busy state
allow kernels compiled with
options
INVARIANTS
and
options
INVARIANT_SUPPORT
to panic if they are not respected.
The
vm_page_assert_sbusied
() function panics
if
m is not shared busied.
The
vm_page_assert_unbusied
() function panics
if
m is not unbusied.
The
vm_page_assert_xbusied
() function panics
if
m is not exclusive busied.
vm_page_aflag(9),
vm_page_alloc(9),
vm_page_deactivate(9),
vm_page_free(9),
vm_page_grab(9),
vm_page_insert(9),
vm_page_lookup(9),
vm_page_rename(9),
VOP_GETPAGES(9)