RFR: 8079315: UseCondCardMark broken in conjunction with CMS precleaning

[Andrew Haley]

On 05/11/2015 11:40 AM, Erik Österlund wrote:

> I have heard statements like this that such mechanism would not work
> on RMO, but never got an explanation why it would work only on
> TSO. Could you please elaborate?  I studied some kernel sources for
> a bunch of architectures and kernels, and it seems as far as I can
> see all good for RMO too.

Dave Dice himself told me that the algorithm is not in general safe
for non-TSO.  Perhaps, though, it is safe in this particular case.  Of
course, I may be misunderstanding him.  I'm not sure of his reasoning
but perhaps we should include him in this discussion.

>From my point of view, I can't see a strong argument for doing this on
AArch64.  StoreLoad barriers are not fantastically expensive there so
it may not be worth going to such extremes.  The cost of a StoreLoad
barrier doesn't seem to be so much more than the StoreStore that we
have to have anyway.

Andrew.