Andreas Dilger wrote:
>> @@ -141,6 +141,7 @@ struct dx_map_entry
>> {
>> u32 hash;
>> u32 offs;
>> + u32 size;
>> };
>
> Hmm, there was something about the size of the dx_map_entry, because
> it is actually built at the end of the target block, that we don't
> want to make it too large.
Yep, that crossed my mind...
> Now, I'm not sure if adding an extra 32-bit field per entry would make
> it too large or not, since I haven't looked at that code in ages. The
> critical factor is whether max_entries = blocksize / min_rec_len would
> consume more than the worst-case amount of space in the target block.
>
> So, because thinking is hard, you might consider just changing the above
> code to use "u16 offs; u16 size;" since we know those are big enough
> variables, and won't increase the size of the map...
That sounds like a good plan. The other possibility is, we don't *have*
to store size in the map, with offset we can always get to the size, too.
>> + for (i = count-1; i >= 0; i--) {
>> + /* is more than half of this entry in last half of the block? */
>> + if (size + map[i].size/2 > blocksize/2)
>> + break;
>> + size += map[i].size;
>> + move++;
>> + }
>> + /* map index at which we will split */
>> + split = count - move;
>
> The rest of this looks fine - I think the "1/2 of median entry" decision
> is the right one as we discussed.
Yes, I forgot to mention that I had discussed this with you a bit
already. :) After drawing a few pictures, this seems like the right
way to go.
-Eric
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