Messages in this thread | | | Date | Tue, 25 Nov 1997 18:32:02 -0500 (EST) | From | "Benjamin C.R. LaHaise" <> | Subject | Re: pageable page tables |
| |
On Tue, 25 Nov 1997, Rik van Riel wrote: ... > It might make some difference when you have suspended some > _large_ simulation because the machine is used interactively > during the day, or when you have _loads_ of processes running, > or...
If you have enough memory to run these kinds of simulations, spending well less than 1% of memory on page tables is a non-issue. But where lots of processes are running... A better idea is to encourage the executable loaders to map processes in an area where they don't cause an additional page to be added to the page table...
> Another concern is that users can grab _all_ of system memory > by having several processes do a 2GB mmap of /dev/zero... > This 'doesn't take any memory' so they can take up as much > (non-pageable) pagetable memory as they want. > In fact, this is the main reason people asked me if I could look > into this... This is one of the biggest denial-of-service holes > still left. (ssstt)
I looked into doing the swappable page table thing, and it would be a pain (too many areas in code assume they won't sleep while walking the page table). The easier (better) approach is to include the page table pages in the RSS of a process, or perhaps add another field indicating the non-swappable RSS. Then, perhaps, better decisions can be made about when the system is really 'out of memory'.
-ben
| |