Re: [RFC][PATCH 3/4] get_user_pages READ fault handling special cases

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Wed, 8 Jul 2009 09:03:44 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:

> On Tue, 7 Jul 2009 09:50:19 -0700 (PDT)
> Linus Torvalds <torvalds@linux-foundation.org> wrote:
> > And I think that if we resurrect zero-page, then we should do it with the 
> > modern equivalent of PAGE_RESERVED, namely the "pte_special()" bit. 
> > Anybody who walks page tables had better already handle special PTE 
> > entries (or we could trivially extend them - in case they currently just 
> > look at the vm_flags and decide that the range can have no special pages).
> > 
> Hm, ok. I'll remove pte_zero and use pte_special instead of it.
> 

Can I make a question ?

As far as I know,

 - ZERO PAGE was not accounted as RSS (in 2.6.9 age)
 - ZERO PAGE was accounted as file_rss (until 2.6.24)

Maybe this one is the change.

http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=
commitdiff;h=4294621f41a85497019fae64341aa5351a1921b7

Is there a special reason to have to account zero page as file_rss ?
If not, pte_special() solution works well. (I think not necessary..)

This was one reason I added pte_zero().

Thanks,
-Kame

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