From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx204.postini.com [74.125.245.204]) by kanga.kvack.org (Postfix) with SMTP id AD0426B0034 for ; Wed, 14 Aug 2013 17:16:15 -0400 (EDT) Received: from /spool/local by e7.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 14 Aug 2013 17:16:14 -0400 Received: from d01relay05.pok.ibm.com (d01relay05.pok.ibm.com [9.56.227.237]) by d01dlp03.pok.ibm.com (Postfix) with ESMTP id BAEB5C90043 for ; Wed, 14 Aug 2013 17:16:09 -0400 (EDT) Received: from d01av04.pok.ibm.com (d01av04.pok.ibm.com [9.56.224.64]) by d01relay05.pok.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id r7ELGBTU164526 for ; Wed, 14 Aug 2013 17:16:11 -0400 Received: from d01av04.pok.ibm.com (loopback [127.0.0.1]) by d01av04.pok.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id r7ELGAMP022636 for ; Wed, 14 Aug 2013 17:16:11 -0400 Date: Wed, 14 Aug 2013 16:16:07 -0500 From: Seth Jennings Subject: Re: [RFC][PATCH] drivers: base: dynamic memory block creation Message-ID: <20130814211607.GB17423@variantweb.net> References: <1376508705-3188-1-git-send-email-sjenning@linux.vnet.ibm.com> <20130814194348.GB10469@kroah.com> <520BE30D.3070401@sr71.net> <20130814203546.GA6200@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130814203546.GA6200@kroah.com> Sender: owner-linux-mm@kvack.org List-ID: To: Greg Kroah-Hartman Cc: Dave Hansen , Nathan Fontenot , Cody P Schafer , Andrew Morton , Lai Jiangshan , "Rafael J. Wysocki" , linux-kernel@vger.kernel.org, linux-mm@kvack.org On Wed, Aug 14, 2013 at 01:35:46PM -0700, Greg Kroah-Hartman wrote: > On Wed, Aug 14, 2013 at 01:05:33PM -0700, Dave Hansen wrote: > > 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. > > Ah, thanks for the explaination, now it makes more sense why they are > both optimizing in different places. Yes, thanks Dave for explaining that for me :) > > But a "cleanup" patch first, and then the "change the logic to go > faster" would be better here, so that we can review what is really > happening. Will do. > > thanks, > > greg k-h > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org