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

[Nick Piggin]

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.

--
SUSE Labs, Novell Inc.

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