man.bsd.lv manual page server

Manual Page Search Parameters
VM_PAGE_BUSY(9) Kernel Developer's Manual VM_PAGE_BUSY(9)

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 () function returns non-zero if the current thread busied m in either exclusive or shared mode. Returns zero otherwise.

The () function must be used to downgrade m from an exclusive busy state to a shared busy state.

The () 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 () function returns non-zero if the current thread busied m in shared mode. Returns zero otherwise.

The () function shared busies m.

The () 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 () function shared unbusies m.

The () attempts to shared busy m. If the operation cannot immediately succeed vm_page_trysbusy() returns 0, otherwise a non-zero value is returned.

The () attempts to exclusive busy m. If the operation cannot immediately succeed vm_page_tryxbusy() returns 0, otherwise a non-zero value is returned.

The () function returns non-zero if the current thread busied m in exclusive mode. Returns zero otherwise.

The () function exclusive busies m.

The () 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 () function panics if m is not shared busied.

The () function panics if m is not unbusied.

The () 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)

August 7, 2013 FreeBSD-12.0