Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1164377AbWLHCUe (ORCPT ); Thu, 7 Dec 2006 21:20:34 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1164378AbWLHCUd (ORCPT ); Thu, 7 Dec 2006 21:20:33 -0500 Received: from omx2-ext.sgi.com ([192.48.171.19]:46131 "EHLO omx2.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1164377AbWLHCUc (ORCPT ); Thu, 7 Dec 2006 21:20:32 -0500 Date: Thu, 7 Dec 2006 18:20:14 -0800 (PST) From: Christoph Lameter To: Jeremy Fitzhardinge cc: Mel Gorman , Andrew Morton , Linux Memory Management List , Linux Kernel Mailing List Subject: Re: [PATCH] Add __GFP_MOVABLE for callers to flag allocations that may be migrated In-Reply-To: <4578BE37.1010109@goop.org> Message-ID: References: <20061204113051.4e90b249.akpm@osdl.org> <20061204120611.4306024e.akpm@osdl.org> <20061204131959.bdeeee41.akpm@osdl.org> <20061204142259.3cdda664.akpm@osdl.org> <20061205112541.2a4b7414.akpm@osdl.org> <20061205214721.GE20614@skynet.ie> <4578BE37.1010109@goop.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1409 Lines: 28 On Thu, 7 Dec 2006, Jeremy Fitzhardinge wrote: > You can also deal with memory hotplug by adding a Xen-style > pseudo-physical vs machine address abstraction. This doesn't help with > making space for contiguous allocations, but it does allow you to move > "physical" pages from one machine page to another if you want to. The > paravirt ops infrastructure has already appeared in -git, and I'll soon > have patches to allow Xen's paravirtualized mmu mode to work with it, > which is a superset of what would be required to implement movable pages > for hotpluggable memory. > > (I don't know if you actually want to consider this approach; I'm just > pointing out that it definitely a bad idea to conflate the two problems > of memory fragmentation and hotplug.) The same can be done using the virtual->physical mappings that exist on many platforms for the kernel address space (ia64 dynamically calculates those, x86_64 uses a page table with 2M pages for mapping the kernel). The problem is that the 1-1 mapping between physical and virtual addresses will have to be (at least partially) sacrificed which may lead to complications with DMA devices. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/