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VM_PAGE_BITS(9)		 BSD Kernel Developer's	Manual	       VM_PAGE_BITS(9)

     vm_page_bits, vm_page_set_validclean, vm_page_clear_dirty,
     vm_page_set_invalid, vm_page_zero_invalid,	vm_page_is_valid,
     vm_page_test_dirty, vm_page_dirty,	vm_page_undirty	-- manage page clean
     and dirty bits

     #include <sys/param.h>
     #include <vm/vm.h>
     #include <vm/vm_page.h>

     vm_page_bits(int base, int	size);

     vm_page_set_validclean(vm_page_t m, int base, int size);

     vm_page_clear_dirty(vm_page_t m, int base,	int size);

     vm_page_set_invalid(vm_page_t m, int base,	int size);

     vm_page_zero_invalid(vm_page_t m, boolean_t setvalid);

     vm_page_is_valid(vm_page_t	m, int base, int size);

     vm_page_test_dirty(vm_page_t m);

     vm_page_dirty(vm_page_t m);

     vm_page_undirty(vm_page_t m);

     vm_page_bits() calculates the bits	representing the DEV_BSIZE range of
     bytes between base	and size.  The byte range is expected to be within a
     single page, and if size is zero, no bits will be set.

     vm_page_set_validclean() flags the	byte range between base	and size as
     valid and clean.  The range is expected to	be DEV_BSIZE aligned and no
     larger than PAGE_SIZE.  If	it is not properly aligned, any	unaligned
     chunks of the DEV_BSIZE blocks at the beginning and end of	the range will
     be	zeroed.

     If	base is	zero and size is one page, the modified	bit in the page	map is
     cleared; as well, the VPO_NOSYNC flag is cleared.

     vm_page_clear_dirty() clears the dirty bits within	a page in the range
     between base and size.  The bits representing the range are calculated by
     calling vm_page_bits().

     vm_page_set_invalid() clears the bits in both the valid and dirty flags
     representing the DEV_BSIZE	blocks between base and	size in	the page.  The
     bits are calculated by calling vm_page_bits().  As	well as	clearing the
     bits within the page, the generation number within	the object holding the
     page is incremented.

     vm_page_zero_invalid() zeroes all of the blocks within the	page that are
     currently flagged as invalid.  If setvalid	is TRUE, all of	the valid bits
     within the	page are set.

     In	some cases, such as NFS, the valid bits	cannot be set in order to
     maintain cache consistency.

     vm_page_is_valid()	checks to determine if the all of the DEV_BSIZE	blocks
     between base and size of the page are valid.  If size is zero and the
     page is entirely invalid vm_page_is_valid() will return TRUE, in all
     other cases a size	of zero	will return FALSE.

     vm_page_test_dirty() checks if a page has been modified via any of	its
     physical maps, and	if so, flags the entire	page as	dirty.
     vm_page_dirty() is	called to modify the dirty bits.

     vm_page_dirty() flags the entire page as dirty.  It is expected that the
     page is not currently on the cache	queue.

     vm_page_undirty() clears all of the dirty bits in a page.

     None of these functions are allowed to block.

     This manual page was written by Chad David	<>.

BSD			       December	1, 2001				   BSD


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