From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail191.messagelabs.com (mail191.messagelabs.com [216.82.242.19]) by kanga.kvack.org (Postfix) with ESMTP id 5153D6B005A for ; Wed, 28 Oct 2009 10:54:25 -0400 (EDT) Received: from d01relay01.pok.ibm.com (d01relay01.pok.ibm.com [9.56.227.233]) by e4.ny.us.ibm.com (8.14.3/8.13.1) with ESMTP id n9SEkO37026717 for ; Wed, 28 Oct 2009 10:46:24 -0400 Received: from d03av06.boulder.ibm.com (d03av06.boulder.ibm.com [9.17.195.245]) by d01relay01.pok.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id n9SEsIJt075854 for ; Wed, 28 Oct 2009 10:54:19 -0400 Received: from d03av06.boulder.ibm.com (loopback [127.0.0.1]) by d03av06.boulder.ibm.com (8.14.3/8.13.1/NCO v10.0 AVout) with ESMTP id n9SEtnWr004299 for ; Wed, 28 Oct 2009 08:55:49 -0600 Subject: Re: RFC: Transparent Hugepage support From: Adam Litke In-Reply-To: <20091028141803.GQ7744@basil.fritz.box> 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> Content-Type: text/plain Date: Wed, 28 Oct 2009 09:54:16 -0500 Message-Id: <1256741656.5613.15.camel@aglitke> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Andi Kleen Cc: 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 15:18 +0100, Andi Kleen wrote: > > My worry are the archs like powerpc where a hugepage doesn't fit in a > > pmd_trans_huge. I think x86 will fit the pmd/pud_trans_huge approach > > in my patch even of 1G pages in the long run, so there is no actual > > long term limitation with regard to x86. The fact is that the generic > > pagetable code is tuned for x86 so no problem there. > > > > What I am unsure about and worries me more are those archs that don't > > use a pmd to map hugepages and to create hugetlb. I am unsure if those > > archs will be able to take advantage of my patch with minor changes to > > it given it is wired to pmd_trans_huge availability. > > I see. Some archs (like IA64 or POWER?) require special VA address > ranges for huge pages, for those doing it fully transparent without > a mmap time flag is likely hard. 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. That doesn't even take into account the (already discussed) page table layout differences between x86 and ppc: http://linux-mm.org/PageTableStructure . -- Thanks, Adam -- 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