Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757246AbYC1Qnl (ORCPT ); Fri, 28 Mar 2008 12:43:41 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757071AbYC1Qn3 (ORCPT ); Fri, 28 Mar 2008 12:43:29 -0400 Received: from e36.co.us.ibm.com ([32.97.110.154]:41236 "EHLO e36.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753423AbYC1Qn2 (ORCPT ); Fri, 28 Mar 2008 12:43:28 -0400 Subject: Re: [PATCH 3 of 4] sparsemem: reduce i386 PAE section size From: Dave Hansen To: Jeremy Fitzhardinge Cc: Christoph Lameter , Ingo Molnar , LKML , Rusty Russell , KAMEZAWA Hiroyuki , Yasunori Goto , Andrew Morton In-Reply-To: <47EC8DD0.4090401@goop.org> References: <47EC574C.10006@goop.org> <47EC8DD0.4090401@goop.org> Content-Type: text/plain Date: Fri, 28 Mar 2008 09:43:19 -0700 Message-Id: <1206722599.7883.119.camel@nimitz.home.sr71.net> Mime-Version: 1.0 X-Mailer: Evolution 2.12.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1230 Lines: 29 On Thu, 2008-03-27 at 23:18 -0700, Jeremy Fitzhardinge wrote: > Christoph Lameter wrote: > > Only works on i386 if you either use sparsemem / vmemmap or not sparsemem > > though. Is there any need for the other sparsemem memory models? Or could > > we disable them like on x86_64? > > Probably, but I don't know what the tradeoffs are. All I want is > hotplug memory. Developers should probably learn the tradeoffs before they go start poking around in code and sending patches. ;) Maybe Christoph has a good idea what the tradeoffs are for the vmemmap variant, but the table-based one is pretty simple. Smaller sections mean that it costs you larger sparsemem structures and more bits in page->flags. But, the smaller the section, the more mem_map[] you might waste. BTW, the current 1G sections were picked because all the hardware we knew of at the time had 512MB dimms that had to be added in pairs. So, we didn't ever have physical hotplug of less than that. -- Dave -- 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/