From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <olof@lixom.net>
Received: from mail.lixom.net (lixom.net [66.141.50.11])
	by ozlabs.org (Postfix) with ESMTP id 6871ADDE0A
	for <linuxppc-dev@ozlabs.org>; Wed,  3 Oct 2007 13:23:42 +1000 (EST)
Date: Tue, 2 Oct 2007 22:27:47 -0500
From: Olof Johansson <olof@lixom.net>
To: Paul Mackerras <paulus@samba.org>
Subject: Re: [PATCH] Use 1TB segments
Message-ID: <20071003032747.GA7822@lixom.net>
References: <18095.59959.698141.565343@cargo.ozlabs.ibm.com>
	<1191350274.18159.279.camel@farscape.rchland.ibm.com>
	<20071003021105.GA6553@lixom.net>
	<18179.1934.821688.836972@cargo.ozlabs.ibm.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
In-Reply-To: <18179.1934.821688.836972@cargo.ozlabs.ibm.com>
Cc: linuxppc-dev@ozlabs.org, Jon Tollefson <kniht@linux.vnet.ibm.com>,
	Will Schmidt <will_schmidt@vnet.ibm.com>
List-Id: Linux on PowerPC Developers Mail List <linuxppc-dev.ozlabs.org>
List-Unsubscribe: <https://ozlabs.org/mailman/listinfo/linuxppc-dev>,
	<mailto:linuxppc-dev-request@ozlabs.org?subject=unsubscribe>
List-Archive: <http://ozlabs.org/pipermail/linuxppc-dev>
List-Post: <mailto:linuxppc-dev@ozlabs.org>
List-Help: <mailto:linuxppc-dev-request@ozlabs.org?subject=help>
List-Subscribe: <https://ozlabs.org/mailman/listinfo/linuxppc-dev>,
	<mailto:linuxppc-dev-request@ozlabs.org?subject=subscribe>

On Wed, Oct 03, 2007 at 01:07:58PM +1000, Paul Mackerras wrote:
> Olof Johansson writes:
> 
> > > This makes the kernel use 1TB segments for all kernel mappings and for
> > > user addresses of 1TB and above, on machines which support them
> > > (currently POWER5+ and POWER6).
> > 
> > PA6T supports them as well :)
> 
> In the patch, we don't actually hard-code the CPU_FTR_1T_SEGMENT bit
> in the cputable entry for any processor; instead we look in the
> ibm,processor-segment-sizes property in the cpu node(s) in the device
> tree. 

Yep, I see that. I just wanted to clarify it for the (future) commit
message.

> Do you want us to add the CPU_FTR_1T_SEGMENT bit to the
> cputable entry for the PA6T, or will your firmware gives the
> ibm,processor-segment-sizes property in the device tree?

Thanks, but we've already got the properties there so it just works.

> > Wouldn't it be possible to stick with 1TB segments for the low range
> > for 64-bit processes as well, and have them allocate their hugepages
> > at >1TB?
> 
> You mean, forbid hugepages below 1TB?  That would be a user-visible
> ABI change.  There are linker scripts for generating executables whose
> text and/or data can go in hugepages, and I believe they put the
> text/data below 1TB.

Hm, good point. Bummer.


-Olof