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Re: The impact to change page size to 16k for cache alias

To: 林建安 <colin@realtek.com.tw>, linux-mips@linux-mips.org
Subject: Re: The impact to change page size to 16k for cache alias
From: Ralf Baechle <ralf@linux-mips.org>
Date: Tue, 31 Mar 2009 10:11:13 +0200
In-reply-to: <20090330082414.GA4797@adriano.hkcable.com.hk>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <9BDA961341E843F29C1C1ECDB54FD0CF@realtek.com.tw> <20090330082414.GA4797@adriano.hkcable.com.hk>
Sender: linux-mips-bounce@linux-mips.org
User-agent: Mutt/1.5.18 (2008-05-17)
On Mon, Mar 30, 2009 at 04:24:15PM +0800, Zhang Le wrote:

> > Hi all,
> > We are willing to use 16k page size to avoid cache alias problem.
> > The Linux version we use is 2.6.12. If we just upgrade mm system to 
> > support 16k page size, what else problems will happen?
> > There is already one thing we know that applications of ELF format  
> > applications should be transformed to be 16k alignment.
> > Another one, we think, highly suspected to be problematic is that many  
> > drivers will be ok for 4k page size but fails for 16k.
> > That is because 4k page size had been seemed to be natural for a very 
> > long long time.
> > Any other problem that shall happen for 16k page size?
> 
> Linux on Loongson 2E and 2F uses 16k page size to avoid cache alias problem, 
> too.
> However, I haven't encountered any problem on Linux kernel itself due to 16k 
> page
> size.
> 
> Anyway, I am not 100% familiar with Loongson patches, so I am not sure whether
> the page size problem is already been taken care of in the patch. If you are
> interested to find out yourself, you can get the whole source here:
> http://repo.or.cz/w/linux-2.6/linux-loongson.git

I've got a report that Fulong is currently only working with 16k pages.  So
4k is no longer the bullet proof choice for all cases :)

  Ralf

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