Re: [RFC] Removing page->flags

[Magnus Damm <magnus.damm@gmail.com>]

On 2/9/06, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> Magnus Damm wrote:
> > Hi Kamezawa-san,
> >
> > On 2/9/06, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> >> Magnus Damm wrote:
> >>> [RFC] Removing page-flags
> >>>
> >>> Moving type A bits:
> >>>
> >>> Instead of keeping the bits together, we spread them out and store a
> >>> pointer to them from pg_data_t.
> >>>
> >> This will annoy people who has a job to look into crash-dump's vmcore..like me ;)
> >> so, I don't like this idea.
> >
> > Hehe, gotcha. =) I also wonder how well it would work with your zone patches.
> >
> My layout-free-zone patches are not affected by this if you use pgdat/section to
> preserve page-flags.

Ok, good.

> To be honest, I'd like to do this
> ==
> struct zone *page_zone(struct page *page)
> {
>         return page->zone;
> }
> ==
> But this increases size of memmap awfully ;( and I can't.
> Current zone-indexing in page-flags is well saving memory space, I think.

With my proposal (Removing type B bits), if you can guarantee that all
your zones have a start address and a size that is aligned to (1 <<
(PAGE_SHIFT * 2)), then the following code should be possible:

struct zone *page_zone(struct page *page)
{
  struct page *parent = virt_to_page(page);

  return (struct zone *)parent->mapping;
}

This assumes that the first entry in mem_map is aligned to PAGE_SIZE,
and that some code has setup parent->mapping to point to the correct
zone. =)

/ magnus

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