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