Function vmem_bt_alloc

freebsd/kern/subr_vmem.c:659–698

* vmem_bt_alloc: Allocate a new page of boundary tags. * * On architectures with uma_small_alloc there is no recursion; no address * space need be allocated to allocate boundary tags. For the others, we * must handle recursion. Boundary tags are necessary to allocate new * boundary tags. * * UMA guarantees that enough tags are held in reserve to allocate a new * page of kva. We dip int

 * we are really out of KVA.
 */
static void *
vmem_bt_alloc(uma_zone_t zone, vm_size_t bytes, int domain, uint8_t *pflag,
    int wait)
{
	vmem_addr_t addr;

	*pflag = UMA_SLAB_KERNEL;

	/*
	 * Single thread boundary tag allocation so that the address space
	 * and memory are added in one atomic operation.
	 */
	mtx_lock(&vmem_bt_lock);
	if (vmem_xalloc(vm_dom[domain].vmd_kernel_arena, bytes, 0, 0, 0,
	    VMEM_ADDR_MIN, VMEM_ADDR_MAX,
	    M_NOWAIT | M_NOVM | M_USE_RESERVE | M_BESTFIT, &addr) == 0) {
		if (kmem_back_domain(domain, kernel_object, addr, bytes,
		    M_NOWAIT | M_USE_RESERVE) == 0) {
			mtx_unlock(&vmem_bt_lock);
			return ((void *)addr);
		}
		vmem_xfree(vm_dom[domain].vmd_kernel_arena, addr, bytes);
		mtx_unlock(&vmem_bt_lock);
		/*
		 * Out of memory, not address space.  This may not even be
		 * possible due to M_USE_RESERVE page allocation.
		 */
		if (wait & M_WAITOK)
			vm_wait_domain(domain);
		return (NULL);
	}
	mtx_unlock(&vmem_bt_lock);
	/*
	 * We're either out of address space or lost a fill race.
	 */
	if (wait & M_WAITOK)
		pause("btalloc", 1);

	return (NULL);
}
#endif

void