---
name: "vm_page_bits"
section: "9"
platform: "linux"
package: "freebsd-manpages"
version: "6.0-5"
release: "Debian 4.0 (Etch)"
platforms: ["linux", "freebsd"]
url: "https://new.carta.tech/vm_page_bits"
---

# vm\_page\_bits(9)

manage page clean and dirty bits

## 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 PG\_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⟩.