Date: Mon, 12 Dec 2005 09:57:31 -0200
From: Marcelo Tosatti <marcelo.tosatti@cyclades.com>
To: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Andi Kleen <ak@suse.de>, Christoph Lameter <clameter@sgi.com>,
       linux-kernel@vger.kernel.org, Hugh Dickins <hugh@veritas.com>,
       linux-mm@kvack.org
Subject: Re: [RFC 3/6] Make nr_pagecache a per zone counter
Message-ID: <20051212115731.GA3599@dmt.cnet>
References: <20051210005440.3887.34478.sendpatchset@schroedinger.engr.sgi.com> <20051210005456.3887.94412.sendpatchset@schroedinger.engr.sgi.com> <20051211183241.GD4267@dmt.cnet> <20051211194840.GU11190@wotan.suse.de> <20051211204943.GA4375@dmt.cnet> <439CF3B1.4050803@yahoo.com.au>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <439CF3B1.4050803@yahoo.com.au>
User-Agent: Mutt/1.4.2.1i
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1325
Lines: 35

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.

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/