Re: Quick question about hyper-threading (also some NUMA stuff)

[Antonio Vargas <wind@cocodriloo.com>]

On Mon, Apr 14, 2003 at 08:39:05AM -0700, Martin J. Bligh wrote:
> > Perhaps it would be good to un-COW pages:
> > 
> > 1. fork process
> > 2. if current node is not loaded, continue as usual
> > 3. if current node is loaded:
> > 3a. pick unloaded node
> > 4b. don't do COW for data pages, but simply copy them to node-local memory
> > 
> > This way, read-write sharings would be replicated for each node.
> 
> Sharing read-write stuff is a total nightmare - you have to deal with
> all the sync stuff, and invalidation. In real-life scenarios, I really
> doubt the complexity is worth it - read-only is quite complex enough,
> thanks ;-) 

I mean MAP_PRIVATE stuff, not MAP_SHARED.

> Theoretically, if you had some pages that were predominatly read-only, 
> and very occasionally got written to, it *might* be worth it. 
> But probably not ;-)
> 
> > Also, keeping an per-node active-page-list and then forcefully copying
> > the page to a node-local page-frame when accesing a page which is
> > active on another node could be good.
> 
> Not sure what you mean by this. wrt the active-page list here's a per-node 
> LRU already. Or you mean something on a per-address-space basis?

Yes, I meant a per-node active LRU. I'd better get a closer look
at what's already done ;)
 
> Yes, faulting the pages in lazily from another node as we touch them is 
> probably the right thing to do. Giving secondary copies some LRU disadvantage
> (perhaps always keeping them on the inactive list, never the active),
> would be fun, but then you get into the whole "who is the primary owner,
> and what do we do when they ditch the page" complexity. The node bitmap
> I suggested earlier might help. But I'd rather keep it simple at first ;-)
> 
> M.

Antonio.