vm_page_busy_downgrade (9)
Leading comments
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NAME
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 referencesSYNOPSIS
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 moptions INVARIANTS 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
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.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 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.
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.
The Fn vm_page_busy_downgrade function must be used to downgrade Fa m from an exclusive busy state to a shared busy state.
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.
The Fn vm_page_busied function returns non-zero if the current thread busied Fa m in shared mode. Returns zero otherwise.
The Fn vm_page_sbusy function shared busies Fa m .
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.
The Fn vm_page_sunbusy function shared unbusies Fa m .
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.
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.
The Fn vm_page_xbusied function returns non-zero if the current thread busied Fa m in exclusive mode. Returns zero otherwise.
The Fn vm_page_xbusy function exclusive busies Fa m .
The Fn vm_page_xunbusy function exclusive unbusies Fa m . Assertions on the busy state allow kernels compiled with options INVARIANTS and options INVARIANT_SUPPORT to panic if they are not respected.
The Fn vm_page_assert_sbusied function panics if Fa m is not shared busied.
The Fn vm_page_assert_unbusied function panics if Fa m is not unbusied.
The Fn vm_page_assert_xbusied function panics if Fa m is not exclusive busied.