From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail202.messagelabs.com (mail202.messagelabs.com [216.82.254.227]) by kanga.kvack.org (Postfix) with ESMTP id AB57C6B004D for ; Thu, 29 Oct 2009 12:00:19 -0400 (EDT) Received: from d03relay05.boulder.ibm.com (d03relay05.boulder.ibm.com [9.17.195.107]) by e33.co.us.ibm.com (8.14.3/8.13.1) with ESMTP id n9TFvhMC002926 for ; Thu, 29 Oct 2009 09:57:43 -0600 Received: from d03av02.boulder.ibm.com (d03av02.boulder.ibm.com [9.17.195.168]) by d03relay05.boulder.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id n9TFxu8s131996 for ; Thu, 29 Oct 2009 09:59:58 -0600 Received: from d03av02.boulder.ibm.com (loopback [127.0.0.1]) by d03av02.boulder.ibm.com (8.14.3/8.13.1/NCO v10.0 AVout) with ESMTP id n9TFw6e1011551 for ; Thu, 29 Oct 2009 09:58:06 -0600 Subject: Re: RFC: Transparent Hugepage support From: Dave Hansen In-Reply-To: <1256741656.5613.15.camel@aglitke> References: <20091026185130.GC4868@random.random> <87ljiwk8el.fsf@basil.nowhere.org> <20091027193007.GA6043@random.random> <20091028042805.GJ7744@basil.fritz.box> <20091028120050.GD9640@random.random> <20091028141803.GQ7744@basil.fritz.box> <1256741656.5613.15.camel@aglitke> Content-Type: text/plain Date: Thu, 29 Oct 2009 08:59:53 -0700 Message-Id: <1256831993.26826.11.camel@nimitz> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Adam Litke Cc: Andi Kleen , Andrea Arcangeli , linux-mm@kvack.org, Marcelo Tosatti , Avi Kivity , Izik Eidus , Hugh Dickins , Nick Piggin , Andrew Morton List-ID: On Wed, 2009-10-28 at 09:54 -0500, Adam Litke wrote: > PowerPC does not require specific virtual addresses for huge pages, but > does require that a consistent page size be used for each slice of the > virtual address space. Slices are 256M in size from 0 to 4G and 1TB in > size above 1TB while huge pages are 64k, 16M, or 16G. Unless the PPC > guys can work some more magic with their mmu, split_huge_page() in its > current form just plain won't work on PowerPC. One answer, at least in the beginning, would be to just ignore this detail. Try to make 16MB pages wherever possible, probably even as 16MB pages in the Linux pagetables. But, we can't promote the MMU to use them until get get a 256MB or 1TB chunk. It will definitely mean some ppc-specific bits when we're changing the segment mapping size, but it's not impossible. That's not going to do any good for the desktop-type users. But, it should be just fine for the HPC or JVM folks. It restricts the users pretty severely, but it gives us *something*. There will be some benefit to using a 16MB Linux page and pte even if we can't back it with 16MB MMU pages, anyway. Remember, a big chunk of the benefit of using 64k pages can be seen even on systems with no 64k hardware pages. -- Dave -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org