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

NAME

     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

SYNOPSIS

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

     int
     vm_page_bits(int base, int size);

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

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

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

     void
     vm_page_zero_invalid(vm_page_t m, boolean_t setvalid);

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

     void
     vm_page_test_dirty(vm_page_t m);

     void
     vm_page_dirty(vm_page_t m);

     void
     vm_page_undirty(vm_page_t m);

DESCRIPTION

     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 chucks 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.

NOTES

     None of these functions are allowed to block.

AUTHORS

     This manual page was written by Chad David <davidc@acns.ab.ca>.

BSD
								 December 1, 2001							       BSD