Messages in this thread | | | Date | Sat, 21 Apr 2001 12:48:48 -0300 (BRST) | From | Rik van Riel <> | Subject | Re: RFC: pageable kernel-segments |
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On Fri, 20 Apr 2001, Stephen C. Tweedie wrote: > On Fri, Apr 20, 2001 at 03:49:30PM +0100, Alan Cox wrote: > > > There is a proposal (several it seems) to make 2.5 replace the conventional > > unix swap with a filesystem of backing store for anonymous objects. That will > > mean each object has its own vm area and inode and thus we can start blowing > > away all user mode page tables when we want. > > Not without major VM overhaul. > > The problem is MAP_PRIVATE, where a single vma can contain both normal > file-backed pages and anonymous pages at the same time. You don't > even know whose anonymous page it is --- a process with anon pages can > fork, so that later on some of the child's anon pages actually come > from the parent's anon space instead of the child's.
Whoooops indeed. I forgot about this mess...
> Right now all of the magic that makes this work is in the page tables. > To remove page tables we'd need additional structures all through the > VM to track anonymous pages, and that's exactly where the FreeBSD VM > starts to get extremely messy compared to ours.
That's because they still seem to use Mach's object chaining.
There's bound to be a much cleaner solution than whatever it is they copied over from Mach ;)
regards,
Rik -- Virtual memory is like a game you can't win; However, without VM there's truly nothing to lose...
http://www.surriel.com/ http://www.conectiva.com/ http://distro.conectiva.com.br/
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