Messages in this thread | | | From | Daniel Phillips <> | Subject | Re: Note describing poor dcache utilization under high memory pressure | Date | Tue, 29 Jan 2002 00:27:29 +0100 |
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On January 29, 2002 12:12 am, Rick Stevens wrote: > Daniel Phillips wrote: > > > Since the page was copied to the child, the child's page table must be > > altered, and since it is shared, it must first be instantiated by the child. > > So after all the dust settles, the parent and child have their own copies of > > a page table page, which differ only at a single location: the child's page > > table points at its freshly made CoW copy, and the parent's page table points > > at the original page. > > > > > The beauty of this is, the page table could just as easily have been shared > > by a sibling of the child, not the parent at all, in the case that the parent > > had already instantiated its own copy of the page table page because of an > > earlier CoW. > > > Ok. Still seems like a bit more copying than necessary.
I think I can show that it's exactly as much copying as necessary, and no more. Oh, the page directory could also be shared and, on a 3 level page table, so could the mid level tables, but that's not a really big win because of the 1K/1 fanout. I.e, we already took care of 99.9% of the problem just by sharing the bottom-level page tables.
> I'd have to look at it a bit more and do some noodling. > > > Confused yet? Welcome to the club ;-) > > Does my head exploding qualify for "confused"? If so, then I'm not > yet "confused". I'm "concerned", since my ears are bleeding (a > precursor to an explosion) ;-p
:-)
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