Re: [RFC 3/6] Make nr_pagecache a per zone counter

[Marcelo Tosatti <marcelo.tosatti@cyclades.com>]

On Mon, Dec 12, 2005 at 02:51:13PM +1100, Nick Piggin wrote:
> Marcelo Tosatti wrote:
> >On Sun, Dec 11, 2005 at 08:48:40PM +0100, Andi Kleen wrote:
> >
> >>>By the way, why does nr_pagecache needs to be an atomic variable on UP 
> >>>systems?
> >>
> >>At least on X86 UP atomic doesn't use the LOCK prefix and is thus quite
> >>cheap. I would expect other architectures who care about UP performance
> >>(= not IA64) to be similar.
> >
> >
> >But in practice the variable does not need to be an atomic type for UP, but
> >simply a word, since stores are atomic on UP systems, no?
> >
> >Several arches seem to use additional atomicity instructions on 
> >atomic functions:
> >
> 
> Yeah, this is to protect from interrupts and is common to most
> load store architectures. It is possible we could have
> atomic_xxx_irq / atomic_xxx_irqsave functions for these, however
> I think nobody has yet demostrated the improvements outweigh the
> complexity that would be added.

Hi Nick,

But nr_pagecache is not accessed at interrupt code, is it? It does
not need to be an atomic type.