Messages in this thread | | | Date | Mon, 28 Jan 2002 19:29:49 -0600 (CST) | From | Oliver Xymoron <> | Subject | Re: Note describing poor dcache utilization under high memory pressure |
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On Mon, 28 Jan 2002, Daniel Phillips wrote:
> copy_page_range > Intead of copying the page tables, just increment their use counts > > zap_page_range: > If a page table is shared according to its use count, just decrement > the use count and otherwise leave it alone. > > handle_mm_fault: > If a page table is shared according to its use count and the faulting > instruction is a write, allocate a new page table and do the work that > would have normally been done by copy_page_range at fork time. > Decrement the use count of the (perhaps formerly) shared page table.
Somewhere in here, the pages have got to all be marked read-only or something. If they're not, then either parent or child writing to non-faulting addresses will be writing to shared memory.
I think something more is needed, such as creating a minimal page table for the child process with read-only mappings to the current %EIP and %EBP pages in it. This gets us past the fork/exec hurdle. Without the exec, we copy over chunks when they're accessed as above in handle_mm_fault. But you can't actually _share_ the page tables without marking the pages themselves readonly.
-- "Love the dolphins," she advised him. "Write by W.A.S.T.E.."
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