From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760165AbYDDT3Q (ORCPT ); Fri, 4 Apr 2008 15:29:16 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756589AbYDDT3A (ORCPT ); Fri, 4 Apr 2008 15:29:00 -0400 Received: from relay2.sgi.com ([192.48.171.30]:35745 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751116AbYDDT3A (ORCPT ); Fri, 4 Apr 2008 15:29:00 -0400 Date: Fri, 4 Apr 2008 12:28:58 -0700 (PDT) From: Christoph Lameter X-X-Sender: clameter@schroedinger.engr.sgi.com To: Jeremy Fitzhardinge cc: Dave Hansen , KAMEZAWA Hiroyuki , Yasunori Goto , Ingo Molnar , LKML Subject: Re: [PATCH 5 of 6] hotplug-memory: add section_ops In-Reply-To: <47F6719E.9010807@goop.org> Message-ID: References: <785fe0877fea0f488bc5.1207267545@localhost> <1207270272.943.27.camel@nimitz.home.sr71.net> <47F5809A.7040307@goop.org> <1207273978.943.82.camel@nimitz.home.sr71.net> <47F5BD6C.30100@goop.org> <1207318946.943.107.camel@nimitz.home.sr71.net> <47F6719E.9010807@goop.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 4 Apr 2008, Jeremy Fitzhardinge wrote: > > Say that you have a very fragmented lowmem-only machine and you want to > > add a section of new mem_map[]. That's 512MB/PAGE_SIZE*sizeof(struct > > page), which is between 4 and 8MB. So, you need 8MB of contiguous pages > > for that mem_map[]. The way we designed it, you could always have that Note that you could use 4k page size chunks for the memmap if its virtualized (CONFIG_SPARSEMEM_VMEMMAP). Instead of a single PMD pointing to a 2MB block you would have the PMD point to a block of ptes that would in turn point to the discontiguous series of 4k pages. The memory is virtually contiguous so all the logic stays the same. What would be needed is some enhancements to the way the memmap is populated.