Function vm_hold_load_pages

freebsd/kern/vfs_bio.c:4878–4908

* vm_hold_load_pages and vm_hold_free_pages get pages into * a buffers address space. The pages are anonymous and are * not associated with a file object. */

 * not associated with a file object.
 */
static void
vm_hold_load_pages(struct buf *bp, vm_offset_t from, vm_offset_t to)
{
	vm_offset_t pg;
	vm_page_t p;
	int index;

	BUF_CHECK_MAPPED(bp);

	to = round_page(to);
	from = round_page(from);
	index = (from - trunc_page((vm_offset_t)bp->b_data)) >> PAGE_SHIFT;
	MPASS((bp->b_flags & B_MAXPHYS) == 0);
	KASSERT(to - from <= maxbcachebuf,
	    ("vm_hold_load_pages too large %p %#jx %#jx %u",
	    bp, (uintmax_t)from, (uintmax_t)to, maxbcachebuf));

	for (pg = from; pg < to; pg += PAGE_SIZE, index++) {
		/*
		 * note: must allocate system pages since blocking here
		 * could interfere with paging I/O, no matter which
		 * process we are.
		 */
		p = vm_page_alloc(NULL, 0, VM_ALLOC_SYSTEM | VM_ALLOC_NOOBJ |
		    VM_ALLOC_WIRED | VM_ALLOC_COUNT((to - pg) >> PAGE_SHIFT) |
		    VM_ALLOC_WAITOK);
		pmap_qenter(pg, &p, 1);
		bp->b_pages[index] = p;
	}
	bp->b_npages = index;
}

/* Return pages associated with this buf to the vm system */
static void