Re: What to expect with the 2.6 VM

Andrea Arcangeli
2003-07-04T00:46:41Z

On Thu, Jul 03, 2003 at 03:21:13PM -0700, William Lee Irwin III wrote:
> On Thu, Jul 03, 2003 at 11:54:31AM -0700, William Lee Irwin III wrote:
> >> I call that application #2.
>
> On Thu, Jul 03, 2003 at 09:33:28PM +0200, Andrea Arcangeli wrote:
> > maybe I'm missing something but protections have nothing to do with
> > remap_file_pages IMHO. That's all about teaching the swap code to
> > reserve more bits in the swap entry and to store the protections there
> > and possibly teaching the page fault not to get confused. It might
> > prefer to use the populate callback too to avoid specializing the
> > pte_none case, but I think the syscall should be different, and it
> > shouldn't have anything to do with the nonlinearity (nor with rmap).
>
> It's obvious what to do about protections.

so you agree it'd better be a separate syscall, also given it seems
the current remap_file_pages api in 2.5 seems unfortunately already
frozen since I think it's wrong as it should only work on VM_NONLINEAR
vmas, it's very unclean to allow remap_file_pages to mangle whatever vma
out there despite it has to deal with truncate etc.. I think the minium
required change to the API is to add a MAP_NONLINEAR that converts in
kernel space to a VM_NONLINEAR. You allocate the mapping with
mmap(MAP_NONLINAER) and only then remap_file_pages will work. This
solves all the current brekages (and it'll be trivial to skip over
VM_NONLINEAR in the 2.4 vm too). (then there's the rmap/mlock/munlock
issue but that's an implementation issue non visible from userspace
[modulo security with the sysctl], this one instead is a API bug IMHO
and it'd better be fixed before people puts the backport in production)
Again, all in my humble opinion.

Andrea