Michael S. Tsirkin <mst <at> redhat.com> writes:
>
> At the moment, memory radix tree is already variable width, but it can
> only skip the low bits of address.
>
> This is efficient if we have huge memory regions but inefficient if we
> are only using a tiny portion of the address space.
>
> After we have built up the map, detect
> configurations where a single L2 entry is valid.
>
> We then speed up the lookup by skipping one or more levels.
> In case any levels were skipped, we might end up in a valid section
> instead of erroring out. We handle this by checking that
> the address is in range of the resulting section.
>
I think this is overkill. It can be done in a simpler way as follows:
phys_page_find(RadixTree* tr, hwaddr index, ...)
{
if (index & rt->invalid_index_mask) {
// not found
}
lp = rt->root;
for (i = rt->nb_levels - 1; i >= 0 && !lp.is_leaf; --i) {
...
This exploits the fact the lower portion of the address space is always
filled, at least in the cases that matter to us.
