From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753871Ab1AXQyG (ORCPT ); Mon, 24 Jan 2011 11:54:06 -0500 Received: from e39.co.us.ibm.com ([32.97.110.160]:44695 "EHLO e39.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753823Ab1AXQyC (ORCPT ); Mon, 24 Jan 2011 11:54:02 -0500 Subject: Re: [PATCH] ARM: mm: Regarding section when dealing with meminfo From: Dave Hansen To: Russell King - ARM Linux Cc: KyongHo Cho , Kukjin Kim , KeyYoung Park , linux-kernel@vger.kernel.org, Ilho Lee , linux-mm@kvack.org, linux-samsung-soc@vger.kernel.org, linux-arm-kernel@lists.infradead.org In-Reply-To: <20110123180532.GA3509@n2100.arm.linux.org.uk> References: <1295516739-9839-1-git-send-email-pullip.cho@samsung.com> <1295544047.9039.609.camel@nimitz> <20110120180146.GH6335@n2100.arm.linux.org.uk> <1295547087.9039.694.camel@nimitz> <20110123180532.GA3509@n2100.arm.linux.org.uk> Content-Type: text/plain; charset="ANSI_X3.4-1968" Date: Mon, 24 Jan 2011 08:52:17 -0800 Message-ID: <1295887937.11047.119.camel@nimitz> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 2011-01-23 at 18:05 +0000, Russell King - ARM Linux wrote: > On Thu, Jan 20, 2011 at 10:11:27AM -0800, Dave Hansen wrote: > > On Thu, 2011-01-20 at 18:01 +0000, Russell King - ARM Linux wrote: > > > > The x86 version of show_mem() actually manages to do this without any > > > > #ifdefs, and works for a ton of configuration options. It uses > > > > pfn_valid() to tell whether it can touch a given pfn. > > > > > > x86 memory layout tends to be very simple as it expects memory to > > > start at the beginning of every region described by a pgdat and extend > > > in one contiguous block. I wish ARM was that simple. > > > > x86 memory layouts can be pretty funky and have been that way for a long > > time. That's why we *have* to handle holes in x86's show_mem(). My > > laptop even has a ~1GB hole in its ZONE_DMA32: > > If x86 is soo funky, I suggest you try the x86 version of show_mem() > on an ARM platform with memory holes. Make sure you try it with > sparsemem as well... x86 uses the generic lib/ show_mem(). It works for any holes, as long as they're expressed in one of the memory models so that pfn_valid() notices them. ARM looks like its pfn_valid() is backed up by searching the (ASM arch-specific) memblocks. That looks like it would be fairly slow compared to the other pfn_valid() implementations and I can see why it's being avoided in show_mem(). Maybe we should add either the MAX_ORDER or section_nr() trick to the lib/ implementation. I bet that would use pfn_valid() rarely enough to meet any performance concerns. -- Dave