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From: Andi Kleen <ak@suse.de>
To: Christoph Lameter <christoph@lameter.com>
Cc: Andi Kleen <ak@suse.de>, Dave Hansen <haveblue@us.ibm.com>,
	linux-mm@kvack.org
Subject: Re: [patch] CONFIG_ARCH_HAS_ATOMIC_UNSIGNED
Date: Sat, 18 Dec 2004 07:50:55 +0100	[thread overview]
Message-ID: <20041218065055.GA5829@wotan.suse.de> (raw)
In-Reply-To: <Pine.LNX.4.58.0412171410240.23925@server.graphe.net>

On Fri, Dec 17, 2004 at 02:11:59PM -0800, Christoph Lameter wrote:
> On Fri, 17 Dec 2004, Andi Kleen wrote:
> 
> > On Fri, Dec 17, 2004 at 11:26:49AM -0800, Christoph Lameter wrote:
> > > On Fri, 17 Dec 2004, Andi Kleen wrote:
> > >
> > > > > Put the order of the page there for compound pages instead of having that
> > > > > in index?
> > > >
> > > > That would waste memory on the 64bit architectures that cannot tolerate
> > > > 32bit atomic flags or on true 32bit architecture.
> > >
> > > Would be great to have 64 bit atomic support to fill this hole then.
> >
> > I think you lost me.   How would that help?
> 
> It would fill the hole on 64 bits if atomic_t would have the native word
> size.

The problem is that that 64bit atomic_t type would end up unaligned.
While that would work in theory on x86-64 I suspect it would be slow even
there. And it would probably not work anywhere else.

And as Dave said they plan to use the upper 32bit of flags for 
CONFIG_NONLINEAR anyways, so it's not even possible.

-Andi
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      reply	other threads:[~2004-12-18  6:50 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2004-12-17  0:44 [patch] CONFIG_ARCH_HAS_ATOMIC_UNSIGNED Dave Hansen
2004-12-17  6:11 ` Andi Kleen
2004-12-17  8:42   ` Dave Hansen
2004-12-17 16:27   ` Christoph Lameter
2004-12-17 16:33     ` Andi Kleen
2004-12-17 19:26       ` Christoph Lameter
2004-12-17 19:37         ` Andi Kleen
2004-12-17 22:11           ` Christoph Lameter
2004-12-18  6:50             ` Andi Kleen [this message]

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