From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx126.postini.com [74.125.245.126]) by kanga.kvack.org (Postfix) with SMTP id 306DC6B0032 for ; Wed, 14 Aug 2013 16:05:39 -0400 (EDT) Message-ID: <520BE30D.3070401@sr71.net> Date: Wed, 14 Aug 2013 13:05:33 -0700 From: Dave Hansen MIME-Version: 1.0 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: owner-linux-mm@kvack.org List-ID: 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 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, 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