RFR (S): Mark scan prefetch

[Aleksey Shipilev]

On 11/08/2016 03:53 PM, Roman Kennke wrote:
> BTW: Are you also planning to write-prefetch? Most users of this
> routine are also writing (copy-object to a different location though..)
> I'd expect even more benefit from that.

Looking at that now, for parallel_evac. For x86, it does not matter.

> Also, what's the reason for not prefetching when doing accurate
> traversal? (not relevant for mark-compact I guess)

The comment in the code says it: it is useless to prefetch, because
oopDesc::size() that we now need for traversal would touch object
contents, at least the klassword. Having redundant prefetch there is a
pessimisation.

Thanks,
-Aleksey