Function swap_pager_alloc

freebsd/vm/swap_pager.c:697–725

* SWAP_PAGER_ALLOC() - allocate a new OBJT_SWAP VM object and instantiate * its metadata structures. * * This routine is called from the mmap and fork code to create a new * OBJT_SWAP object. * * This routine must ensure that no live duplicate is created for * the named object request, which is protected against by * holding the sw_alloc_sx lock in case handle != NULL. */

 *	holding the sw_alloc_sx lock in case handle != NULL.
 */
static vm_object_t
swap_pager_alloc(void *handle, vm_ooffset_t size, vm_prot_t prot,
    vm_ooffset_t offset, struct ucred *cred)
{
	vm_object_t object;

	if (handle != NULL) {
		/*
		 * Reference existing named region or allocate new one.  There
		 * should not be a race here against swp_pager_meta_build()
		 * as called from vm_page_remove() in regards to the lookup
		 * of the handle.
		 */
		sx_xlock(&sw_alloc_sx);
		object = vm_pager_object_lookup(NOBJLIST(handle), handle);
		if (object == NULL) {
			object = swap_pager_alloc_init(handle, cred, size,
			    offset);
			if (object != NULL) {
				TAILQ_INSERT_TAIL(NOBJLIST(object->handle),
				    object, pager_object_list);
			}
		}
		sx_xunlock(&sw_alloc_sx);
	} else {
		object = swap_pager_alloc_init(handle, cred, size, offset);
	}
	return (object);
}

/*
 * SWAP_PAGER_DEALLOC() -	remove swap metadata from object