From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755833Ab1CAI3W (ORCPT ); Tue, 1 Mar 2011 03:29:22 -0500 Received: from mail-fx0-f46.google.com ([209.85.161.46]:59379 "EHLO mail-fx0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755422Ab1CAI3U (ORCPT ); Tue, 1 Mar 2011 03:29:20 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; b=oihSyUQOrijoNA3C047QYXM5nIlNB8prSIEFTYPXu/AF//Z8sDln78O/Uom5WjwSj5 0e5zdeHVrdaf0Yxaz6caLFDRK3rpnlXvQLg7vpSeB1PuY8eI7N/C5aBACFcG2tgE5Vw2 kMCyAOoykVBfSg+t2e56nQG/Bzjg6Wop8JRUw= Date: Tue, 1 Mar 2011 09:29:15 +0100 From: Tejun Heo To: "H. Peter Anvin" Cc: Yinghai Lu , x86@kernel.org, Ingo Molnar , Thomas Gleixner , linux-kernel@vger.kernel.org Subject: Re: questions about init_memory_mapping_high() Message-ID: <20110301082915.GC26074@htj.dyndns.org> References: <20110223171945.GI26065@htj.dyndns.org> <4D6BE614.3010007@zytor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4D6BE614.3010007@zytor.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hey, (sorry about the earlier empty reply, fat finger on my phone) On Mon, Feb 28, 2011 at 10:14:44AM -0800, H. Peter Anvin wrote: > > 1. The only rationale given in the commit description is that a > > RED-PEN is killed, which was the following. > > > > /* > > * RED-PEN putting page tables only on node 0 could > > * cause a hotspot and fill up ZONE_DMA. The page tables > > * need roughly 0.5KB per GB. > > */ > > > > This already wasn't true with top-down memblock allocation. > > > > The 0.5KB per GiB comment is for 32bit w/ 3 level mapping. On > > 64bit, it's ~4KiB per GiB when using 2MiB mappings and, well, very > > small per GiB if 1GiB mapping is used. Even with 2MiB mapping, > > 1TiB mapping would only be 4MiB. Under ZONE_DMA, this could be > > problematic but with top-down this can't be a problem in any > > realistic way in foreseeable future. > > > > It's true on 64 bits too when PAE is not available (e.g. with Xen.) Hmm... I don't follow. Can you elaborate? If PAE is not available for whatever reason, the physical memory is limited to 4GiB but I don't follow what that has to do with the above. Thanks. -- tejun