Re: swapout selection change in pre1

[Roman Zippel <roman@augan.com>]

Hi,

Rik van Riel wrote:

> > Reverse mapping is basically not simple at all. For each page table entry,
> > you need a
> >
> >       struct reverse_map {
> >               /* actual pte pointer is implied by location,
> >                  if you implement this cleverly, but still
> >                  needed, of course */
> >               struct reverse_map *prev, *next;
> >               struct vm_struct *vma;
> >       };
> 
> Actually, you need only 2 pointers per page.
> 
> struct reverse_map {
>         pte_t * pte;
>         struct reverse_map * next;
> };

To keep memory usage low and to still be reasonably fast, we could
restrict the size of a vma to two mmu levels and cache a pointer to the
pmd table in the vma, so you have less to lookup in the page table. It
would also speed up normal mapping/unmapping of entries for
architectures with more than 2 mmu levels. Generic mm code had mostly
only to deal with two mmu levels and e.g could call "pmd =
pmd_alloc_vma(vma, address);" instead of "pgd = pgd_offset(mm, address);
pmd = pmd_alloc(pgd, address);". No idea if this is fast enough for
balancing, but it would simplify other parts. :-)

bye, Roman
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