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VM_PAGE_BUSY(9) FreeBSD Kernel Developer's Manual VM_PAGE_BUSY(9)
NAME
vm_page_busied, vm_page_busy_downgrade, vm_page_busy_sleep,
vm_page_sbusied, vm_page_sunbusy, vm_page_trysbusy, vm_page_tryxbusy,
vm_page_xbusied, vm_page_xunbusy, vm_page_assert_sbusied,
vm_page_assert_unbusied, vm_page_assert_xbusied - protect page identity
changes and page content references
SYNOPSIS
#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);
bool
vm_page_busy_sleep(vm_page_t m, const char *msg, int allocflags);
int
vm_page_sbusied(vm_page_t m);
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_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);
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.
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() checks the busy state of the page m and puts the
invoking thread to sleep if the page is busy. The VM object for the page
must be locked. The allocflags parameter must be either 0, in which case
the function will sleep if the page is busied, or VM_ALLOC_IGN_SBUSY, in
which case the function will sleep only if the page is exclusively
busied. A return value of true indicates that the invoking thread was
put to sleep and that the object was unlocked. A return value of false
indicates that the invoking thread did not sleep and the object remains
locked. 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_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_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.
SEE ALSO
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)
FreeBSD 14.0-RELEASE-p6 November 11, 2021 FreeBSD 14.0-RELEASE-p6