Function vm_page_set_valid_range

freebsd/vm/vm_page.c:5017–5062

* vm_page_set_valid_range: * * Sets portions of a page valid. The arguments are expected * to be DEV_BSIZE aligned but if they aren't the bitmap is inclusive * of any partial chunks touched by the range. The invalid portion of * such chunks will be zeroed. * * (base + size) must be less then or equal to PAGE_SIZE. */

 *	(base + size) must be less then or equal to PAGE_SIZE.
 */
void
vm_page_set_valid_range(vm_page_t m, int base, int size)
{
	int endoff, frag;
	vm_page_bits_t pagebits;

	vm_page_assert_busied(m);
	if (size == 0)	/* handle degenerate case */
		return;

	/*
	 * If the base is not DEV_BSIZE aligned and the valid
	 * bit is clear, we have to zero out a portion of the
	 * first block.
	 */
	if ((frag = rounddown2(base, DEV_BSIZE)) != base &&
	    (m->valid & (1 << (base >> DEV_BSHIFT))) == 0)
		pmap_zero_page_area(m, frag, base - frag);

	/*
	 * If the ending offset is not DEV_BSIZE aligned and the
	 * valid bit is clear, we have to zero out a portion of
	 * the last block.
	 */
	endoff = base + size;
	if ((frag = rounddown2(endoff, DEV_BSIZE)) != endoff &&
	    (m->valid & (1 << (endoff >> DEV_BSHIFT))) == 0)
		pmap_zero_page_area(m, endoff,
		    DEV_BSIZE - (endoff & (DEV_BSIZE - 1)));

	/*
	 * Assert that no previously invalid block that is now being validated
	 * is already dirty.
	 */
	KASSERT((~m->valid & vm_page_bits(base, size) & m->dirty) == 0,
	    ("vm_page_set_valid_range: page %p is dirty", m));

	/*
	 * Set valid bits inclusive of any overlap.
	 */
	pagebits = vm_page_bits(base, size);
	if (vm_page_xbusied(m))
		m->valid |= pagebits;
	else
		vm_page_bits_set(m, &m->valid, pagebits);
}

/*
 * Set the page dirty bits and free the invalid swap space if