Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933152Ab3HNUFj (ORCPT ); Wed, 14 Aug 2013 16:05:39 -0400 Received: from www.sr71.net ([198.145.64.142]:42212 "EHLO blackbird.sr71.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933005Ab3HNUFi (ORCPT ); Wed, 14 Aug 2013 16:05:38 -0400 Message-ID: <520BE30D.3070401@sr71.net> Date: Wed, 14 Aug 2013 13:05:33 -0700 From: Dave Hansen User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130803 Thunderbird/17.0.8 MIME-Version: 1.0 To: Greg Kroah-Hartman CC: Seth Jennings , Nathan Fontenot , Cody P Schafer , Andrew Morton , Lai Jiangshan , "Rafael J. Wysocki" , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [RFC][PATCH] drivers: base: dynamic memory block creation References: <1376508705-3188-1-git-send-email-sjenning@linux.vnet.ibm.com> <20130814194348.GB10469@kroah.com> In-Reply-To: <20130814194348.GB10469@kroah.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1785 Lines: 34 On 08/14/2013 12:43 PM, Greg Kroah-Hartman wrote: > On Wed, Aug 14, 2013 at 02:31:45PM -0500, Seth Jennings wrote: >> ppc64 has a normal memory block size of 256M (however sometimes as low >> as 16M depending on the system LMB size), and (I think) x86 is 128M. With >> 1TB of RAM and a 256M block size, that's 4k memory blocks with 20 sysfs >> entries per block that's around 80k items that need be created at boot >> time in sysfs. Some systems go up to 16TB where the issue is even more >> severe. > > The x86 developers are working with larger memory sizes and they haven't > seen the problem in this area, for them it's in other places, as I > referred to in my other email. The SGI guys don't run normal distro kernels and don't turn on memory hotplug, so they don't see this. I do the same in my testing of large-memory x86 systems to speed up my boots. I'll go stick it back in there and see if I can generate some numbers for a 1TB machine. But, the problem on x86 is at _worst_ 1/8 of the problem on ppc64 since the SECTION_SIZE is so 8x bigger by default. Also, the cost of creating sections on ppc is *MUCH* higher than x86 when amortized across the number of pages that you're initializing. A section on ppc64 has to be created for each (2^24/2^16)=256 pages while one on x86 is created for each (2^27/2^12)=32768 pages. Thus, x86 folks with our small pages and large sections tend to be focused on per-page costs. The ppc folks with their small sections and larger pages tend to be focused on the per-section costs. -- 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/